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A Raman-active boronate modified surface-enhanced Raman scattering (SERS) microporous array chip based on the enzymatic reaction was constructed for reliable, sensitive, and quantitative monitoring of D-Proline (D-Pro) and D-Alanine (D-Ala) in saliva. Initially, 3-mercaptophenylboronic acid (3-MPBA) was bonded to Au-coated Si nanocrown arrays (Au/SiNCA) via Au–S bonding. Following this, H2O2 obtained from D-amino acid oxidase (DAAO)-specific catalyzed D-amino acids (D-AAs) further reduced 3-MPBA to 3-hydroxythiophenol (3-HTP) with a new Raman peak at 882 cm−1. Meanwhile, the original characteristic peak at 998 cm−1 remained unchanged. Therefore, the I882/I998 ratio increased with increasing content of D-AAs in the sample to be tested, allowing D-AAs to be quantitatively detected. The Au/SiNCA with large-area periodic crown structure prepared provided numerous, uniform "hot spots," and the microporous array chip with 16 detection units was employed as the platform for SERS analysis, realizing high-throughput, high sensitivity, high specificity and high-reliability quantitative detection of D-AAs (D-Pro and D-Ala). The limits of detection (LOD) were down to 10.1 µM and 13.7 µM throughout the linear range of 20–500 µM. The good results of the saliva detection suggested that this SERS sensor could rapidly differentiate between early-stage gastric cancer patients and healthy individuals. [ABSTRACT FROM AUTHOR]

Purpose: There is currently no ideal radiotracer for imaging bacterial infections. Radiolabelled d-amino acids are promising candidates because they are actively incorporated into the peptidoglycan of the bacterial cell wall, a structural feature which is absent in human cells. This work describes fluorine-18 labelled analogues of d-tyrosine and d-methionine, O-(2-[18F]fluoroethyl)-d-tyrosine (d-[18F]FET) and S-(3-[18F]fluoropropyl)-d-homocysteine (d-[18F]FPHCys), and their pilot evaluation studies as potential radiotracers for imaging bacterial infection. Procedures: d-[18F]FET and d-[18F]FPHCys were prepared in classical fluorination-deprotection reactions, and their uptake in Staphylococcus aureus and Pseudomonas aeruginosa was evaluated over 2 h. Heat killed bacteria were used as controls. A clinically-relevant foreign body model of S. aureus infection was established in Balb/c mice, as well as a sterile foreign body to mimic inflammation. The ex vivo biodistribution of d-[18F]FPHCys in the infected and inflamed mice was evaluated after 1 h, by dissection and gamma counting. The uptake was compared to that of [18F]FDG. Results: In vitro uptake of both d-[18F]FET and d-[18F]FPHCys was specific to live bacteria. Uptake was higher in S. aureus than in P. aeruginosa for both radiotracers, and of the two, higher for d-[18F]FPHCys than d-[18F]FET. Blocking experiments with non-radioactive d-[19F]FPHCys confirmed specificity of uptake. In vivo, d-[18F]FPHCys had greater accumulation in S. aureus infection compared with sterile inflammation, which was statistically significant. As anticipated, [18F]FDG showed no significant difference in uptake between infection and inflammation. Conclusions: d-[18F]FPHCys uptake was higher in infected tissues than inflammation, and represents a fluorine-18 labelled d-AA with potential to detect a S. aureus reference strain (Xen29) in vivo. Additional studies are needed to evaluate uptake of this radiotracer in clinical isolates. [ABSTRACT FROM AUTHOR]

Biomarkers that accurately reflect renal function are essential in management of chronic kidney diseases (CKD). However, in children, age/physique and medication often alter established renal biomarkers. We studied whether amino acid enantiomers in body fluids correlate with renal function and whether they are influenced by physique or steroid medication during development. We conducted a prospective study of children 2 to 18 years old with and without CKD. We analyzed associations of serine/asparagine enantiomers in body fluids with major biochemical parameters as well as physique. To study consequences of kidney dysfunction and steroids on serine/asparagine enantiomers, we generated juvenile mice with uninephrectomy, ischemic reperfusion injury, or dexamethasone treatment. We obtained samples from 27 children, of which 12 had CKD due to congenital (n = 7) and perinatal (n = 5) causes. Plasma d-asparagine and the d/l-serine ratio had robust, positive linear associations with serum creatinine and cystatin C, and detected CKD with high sensitivity and specificity, uninfluenced by body size or biochemical parameters. In the animal study, kidney dysfunction increased plasma d-asparagine and the d/l-serine ratio, but dexamethasone treatment did not. Thus, plasma d-asparagine and the d/l-serine ratio can be useful markers for renal function in children. [ABSTRACT FROM AUTHOR]

Background: Patients with chronic kidney disease (CKD) reportedly show dysbiosis, which is the imbalance of gut microbiome. Dysbiosis increases the uremic toxin level in the intestine, and uremic toxins transfer into the blood, causing CKD progression. Sake lees, a traditional Japanese fermented food, may help reduce uremic toxins by altering the gut microbiome. Additionally, D-alanine, which is present in sake lees, may have a renoprotective effect. The present pilot study aims to evaluate the effect of adding sake lees to the standard CKD dietary therapy in reducing blood uremic toxins. Methods: This pilot study is a single-center, open-label, randomized controlled trial. Twenty-four patients with CKD will be enrolled and allocated 1:1 to the intervention and control groups. The intervention group will receive standard CKD dietary therapy with an additional intake of 50 g of sake lees per day for 8 weeks, whereas the control group will only receive standard CKD dietary therapy. The primary endpoint is the change in serum indoxyl sulfate after 8 weeks. The secondary endpoint is the plasma D-alanine and fecal microbiome changes. Conclusion: This pilot study provides insight into the development of a new diet focused on gut microbiome and D-amino acids in patients with CKD. Clinical trial registration: This protocol was approved by the Clinical Trial Review Board of Kanazawa University Hospital on October 27, 2022 (2022-001 [6139]) and available to the public on the website of the Japan Registry of Clinical Trials on November 22, 2022 (jRCT1040220095). [ABSTRACT FROM AUTHOR]

Approximately 12% of histone H2B molecules in mammalian brain contain a modification wherein Asp25 is present as the d-enantiomer, and is mostly linked to Gly26 via the side-chain carboxyl. Here we (1) demonstrate the high specificity of a polyclonal antibody to this modification, and (2) use this Ab to demonstrate that this modification is enriched in brain relative to liver, thymus, and HeLa cells. [ABSTRACT FROM AUTHOR]

The study of biominerals of a pathogenic nature in organisms is relevant and necessary for establishing the mechanism of their formation and solving many practical issues. Recently, intensive research has been carried out in the field of biochemistry of D-amino acids, it is believed that they can be potential biomarkers of various pathological processes in the human body. The presence of enantiomers of amino acids and their role in the mechanism of formation of gallstones, the issue has not yet been studied. The paper presents data on the distribution of D-enantiomers of amino acids, their content and ratio with L-forms in the composition of gallstones. A comparative analysis of the obtained results on gallstones with urinary stones is shown. It has been established that there is a relationship between the enantiomers of amino acids and the calcium mineral component. [ABSTRACT FROM AUTHOR]

D-Amino acids are regulatory molecules that affect biological processes. Therefore, being able to accurately detect and quantify these compounds is important for understanding their impact on nutrition and health. There is a paucity of information regarding d-amino acids in human milk. We developed a fast method for simultaneous analysis of amino acid enantiomers in human milk using liquid chromatography with tandem mass spectrometry. The method enables the separation of 41 amino acids without chemical derivatization. Our results revealed that human milk from mothers of preterm infants contains concentrations of d-amino acids that range from 0.5 to 45% that of their l-counterparts and that levels of most d-amino acids decrease as the milk production matures. Moreover, we found that Holder pasteurization of milk does not cause racemization of l-amino acids. To our knowledge, this is the first study to describe percentages of d-amino acid levels in human milk; changes in d-amino acid concentration as the milk matures; and the effect of Holder pasteurization on d- and l-amino acid concentrations in human milk. [ABSTRACT FROM AUTHOR]

Neurodegenerative diseases pose significant challenges to healthcare systems globally due to their complex etiology and relentless progression, often rendering conventional treatments ineffective. Recent advances have spotlighted excitatory amino acids, particularly D-amino acids, once considered as products of metabolism of the microbiota or deriving from food intake. This review explores the role of D-amino acids in mitigating excitotoxicity—a process characterized by excessive calcium influx through aberrant N-methyl-D-aspartate receptor (NMDAR) activation, which is implicated in the pathogenesis of diseases like Alzheimer's disease. By providing alternative pathways for neuronal signaling and protecting against excitotoxic damage, D-amino acids offer a novel approach to reversing neurodegenerative trajectories. Future research should focus on elucidating the detailed mechanisms of action of these compounds, evaluating their therapeutic potential through rigorous preclinical and clinical trials, and developing effective delivery systems to optimize their neuroprotective effects. This emerging field holds promise for developing innovative treatment strategies that could significantly improve outcomes for patients with neurodegenerative disorders. [ABSTRACT FROM AUTHOR]

Introduction: Terasi is a fermented shrimp paste unique to Indonesia and is used in dishes to add umami and saltiness. In a previous study, the controlled fermentation of terasi was optimized using starters containing three bacterial isolates: Staphylococcus saprophyticus, Bacillus subtilis, and Lactobacillus murinus. However, the influence of controlled fermentation using these starters on the metabolites in terasi has not yet been studied. Objectives: Therefore, this study aimed to investigate the effect of controlled fermentation on taste-related metabolites in terasi using a metabolomics approach. Results: Non-targeted analysis indicated that amino acids contributed to variations during fermentation. Subsequently, targeted analysis of amino acids revealed that terasi subjected to controlled fermentation using a starter with a 2:1:2 ratio of S. saprophyticus, B. subtilis, and L. murinus, respectively, resulted in a product containing d-amino acids, such as d-Asp, d-Gln, and d-Leu that was unique when compared to other terasi products prepared using controlled fermentation. Genetic analysis of isolates from the terasi produced using controlled fermentation was also carried out, and this is the first study to suggest that Staphylococcus spp. has the potential to produce d-amino acids. Conclusion: In conclusion, the ratio of bacterial species in starter cultures used in controlled fermentation influenced the amino acid profile of the product and starters with a higher ratio of Staphylococcus spp. may result in the production of d-amino acids. [ABSTRACT FROM AUTHOR]

Plasma amino acids reflect the dynamics of amino acids in organs and their levels have clinical significance. Amino acids as clinical indicators have been evaluated as a mixture of d- and l-amino acids because d-enantiomers are believed to be physiologically nonexistent. However, it has become clear that some d-amino acids are synthesized by endogenous enzymes and symbiotic bacteria. Here, using a two-dimensional HPLC system, we measured enantiomers of all proteinogenic amino acids in plasma and urine and analyzed for correlation with other biochemical parameters in humans who underwent health checkups at our institutional hospital. Four d-amino acids (d-asparagine, d-alanine, d-serine, and d-proline) were detected in the plasma, amounting to less than 1% of the quantities of l-amino acids, but in the urine at several tens of percent, showing that d-amino acids have much higher fractional excretion than their L-counterparts. Detected plasma d-amino acids and d-/l-amino acid ratios were well correlated with renal parameters, such as blood urea nitrogen, creatinine, and cystatin C. On the other hand, a set of plasma l-amino acids were associated with body mass index and correlated with metabolic parameters such as liver enzymes, lipids, blood glucose, and uric acid. Thus, chiral resolution of plasma amino acids revealed totally different associations of the enantiomers with organ functions, and warrants further investigation for clinical and laboratory usefulness. [ABSTRACT FROM AUTHOR]

This article is devoted to the patenting of proteins, containing D-isoforms of amino acids, its potential problems and perspectives. Today, technologies for the biosynthesis of protein constructs with nonstandard amino acids in their composition are among the most promising and rapidly developing areas of biotechnology, along with genome editing technologies, due to the cheapening of the solid-phase synthesis process and the appearance of modified ribosomes that use nonstandard amino acids in ribosomal synthesis. This article contains materials indicating the relevance and interest of inventors in this area. Due to the fact that changes in the amino acid sequence of a known protein, consisting of a chain of L-amino acids, by converting the original L-amino acids into D-form, leads to unexpected functional and physicochemical changes of the protein, broad prospects open up for the creation of new drugs, enzymes, pesticides, and other protein products used in various industries, including medicine, food, agriculture, and light industry. Also, this article also touches upon changes in WIPO Standards relating to presentation sequences in terms of the display of D-amino acids in sequences according to WIPO standard ST.25 or ST.26. Here, we describe the potential problems that may arise in the process of patent examination of such applications, e.g., the case when identical sequences of D- and L-proteins having different biological properties. [ABSTRACT FROM AUTHOR]

Background: l-amino acids are the predominant forms of organic molecules on the planet, but recent studies have revealed that various foods contain d-amino acids, the enantiomers of l-amino acids. Though diet plays important roles in both the development and progression of inflammatory bowel disease (IBD), to our best knowledge, there has been no report on any potential interactions between d-amino acids and IBD. In this report, we aim to assess the effects of d-serine in a murine model of IBD. Materials and methods: To induce chronic colitis, naïve CD4 T cells (CD4+ CD62+ CD44low) from wild-type mice were adoptively transferred into Rag2−/− mice, after or before the mice were orally administered with d-serine. In vitro proliferation assays were performed to assess naïve CD4 T cell activation under the Th-skewing conditions in the presence of d-serine. Results: Mice treated with d-serine prior to the induction of colitis exhibited a reduction in T-cell infiltration into the lamina propria and colonic inflammation that were not seen in mice fed with water alone or l-serine. Moreover, d-serine suppressed the progression of chronic colitis when administered after the disease induction. Under in vitro conditions, d-serine suppressed the proliferation of activated CD4 T cells and limited their ability to differentiate to Th1 and Th17 cells. Conclusion: Our results suggest that d-serine not only can prevent, but also has efficacious effects as a treatment for IBD. [ABSTRACT FROM AUTHOR]

Objective: Our aim was to assess the anti-biofilm ability of previously unverified individual D-amino acids (DAAs), to produce plasma polymer encapsulated DAAs (PPEDAAs), to measure the shell thickness and subsequent release of DAAs, and to assess the effects of PPEDAAs on Enterococcus faecalis biofilms. Materials and methods: Microtitre tray assays were used to evaluate the effect of individual DAAs (D-leucine, D-methionine, D-tryptophan, and D-tyrosine) on E. faecalis biofilms of different maturity. A mixture and individual DAAs were encapsulated with a plasma polymer for 10, 20, 40, and 60 min. The shell thickness of PPEDAAs was analyzed by ultra-high-resolution scanning electron microscopy. The release of DAAs from the PPEDAAs encapsulated for 60 min was measured over 7 days using high-performance liquid chromatography. Static biofilms were used to assess the effect of PPEDAAs on E. faecalis biofilms. Results: Individual DAAs reduced biofilm formation to various degrees, according to the DAA and the experimental times. The shell thicknesses of the PPEDAAs ranged between 31 and 76 nm and increased with encapsulation time. Diffusion of DAAs from the PPEDAAs occurred over 60 min for encapsulated D-leucine, D-methionine, and D-tyrosine and up to 7 days for D-tryptophan. PPEDAAs disrupted biofilms at every experimental time. Conclusions: PPEDAAs of various shell thickness can be produced with the proposed methodology, DAAs are subsequently released, and the anti-biofilm activity remains unaltered. Clinical relevance: Individual DAAs and PPEDAAs have anti-biofilm ability and can be considered as part of a biological strategy in endodontics. [ABSTRACT FROM AUTHOR]

The flavoenzyme d-amino acid oxidase (DAAO) is deputed to the degradation of d-enantiomers of amino acids. DAAO plays various relevant physiological roles in different organisms and tissues. Thus, it has been recently suggested that the goblet cells of the mucosal epithelia secrete into the lumen of intestine, a processed and active form of DAAO that uses the intestinal d-amino acids to generate hydrogen peroxide (H2O2), an immune messenger that helps fighting gut pathogens, and by doing so controls the homeostasis of gut microbiota. Here, we show that the DAAO form lacking the 1–16 amino acid residues (the putative secretion signal) is unstable and inactive, and that DAAO is present in the epithelial layer and the mucosa of mouse gut, where it is largely proteolyzed. In silico predicted DAAO-derived antimicrobial peptides show activity against various Gram-positive and Gram-negative bacteria but not on Lactobacilli species, which represent the commensal microbiota. Peptidomic analysis reveals the presence of such peptides in the mucosal fraction. Collectively, we identify a novel mechanism for gut microbiota selection implying DAAO-derived antimicrobial peptides which are generated by intestinal proteases and that are secreted in the gut lumen. In conclusion, we herein report an additional, ancillary role for mammalian DAAO, unrelated to its enzymatic activity. [ABSTRACT FROM AUTHOR]

On the primitive Earth, both l- and d-amino acids would have been present. However, only l-amino acids are essential blocks to construct proteins in modern life. To study the relative stability of d-amino acid substituted peptides, a variety of computational methods were applied. Ten prebiotic amino acids (Gly, Ala, Asp, Glu, Ile, Leu, Pro, Ser, Thr, and Val) were previously determined by multiple meteorite, spark discharge, and hydrothermal vent studies. Some previously reported early Earth polypeptide analogs were focused on in this study. Tripeptides composed of only Asp, Ser, and Val exemplified that different positions (i.e., N-terminus, C-terminus, and middle) made a difference in the minimal folding energy of peptides, while the chemical classification of amino acid (hydrophobic, acidic, or hydroxylic) did not show a significant difference. Hierarchical cluster analysis for dipeptides with all possible combinations of the proposed ten prebiotic amino acids and their d-amino acid substituted derivatives generated five clusters. Primordial simple polypeptides were modeled to test the significance of molecular fluctuations, secondary structure occupancies, and folding energy differences based on these clusters. We found peptides with α-helices, long β-sheets, and long loops are usually less sensitive to d-amino acid replacements in comparison to short β-sheets. Intriguingly, amongst 129 d-amino acid residues, mutation sensitivity profiles presented that the ratio of more to less stable residues was about 1. In conclusion, some combinations of a mixture of l- and d-amino acids can potentially act as essential building blocks of life. [ABSTRACT FROM AUTHOR]

d-Aspartate, d-serine and d-alanine are a regular occurrence in mammalian endocrine tissues, though in amounts varying with the type of gland. The pituitary gland, pineal gland, thyroid, adrenal glands and testis contain relatively large amounts of d-aspartate in all species examined. d-alanine is relatively abundant in the pituitary gland and pancreas. High levels of d-serine characterize the hypothalamus. d-leucine, d-proline and d-glutamate are generally low. The current knowledge of physiological roles of d-amino acids in endocrine tissues is far from exhaustive, yet the topic is attracting increasing interest because of its potential in pharmacological application. d-aspartate is known to act at all levels of the hypothalamus–pituitary–testis axis, playing a key role in reproductive biology in several vertebrate classes. An involvement of d-amino acids in the endocrine function of the pancreas is emerging. d-Aspartate has been immunolocalized in insulin-containing secretory granules in INS-1 E clonal β cells and is co-secreted with insulin by exocytosis. Specific immunolocalization of d-alanine in pituitary ACTH-secreting cells and pancreatic β-cells suggests that this amino acid participates in blood glucose regulation in mammals. By modulating insulin secretion, d-serine probably participates in the control of systemic glucose metabolism by modulating insulin secretion. We anticipate that future investigation will significantly increase the functional repertoire of d-amino acids in homeostatic control. [ABSTRACT FROM AUTHOR]

N-methyl-d-aspartate (NMDA) receptors, which are widely present in the central nervous system, have also been found to be up-regulated in a variety of cancer cells and tumors and they can play active roles in cancer cell growth regulation. NMDA receptor antagonists have been found to affect cancer cell viability and interfere with tumor growth. Moreover, cancer cells also have been shown to have elevated levels of some d-amino acids. Two human skin cell lines: Hs 895.T skin cancer and Hs 895.Sk skin normal cells were investigated. They were derived from the same patient to provide tumor and normal counterparts for comparative studies. The expression of specific NMDA receptors was confirmed for the first time in both skin cell lines. Dizocilpine (MK-801) and memantine, NMDA receptor channel blockers, were found to inhibit the growth of human skin cells by reducing or stopping NMDA receptor activity. Addition of d-Ser, d-Ala, or d-Asp, however, significantly reversed the antiproliferative effect on the human skin cells triggered by MK-801 or memantine. Even more interesting was the finding that the specific intracellular composition of a few relatively uncommon amino acids was selectively elevated in skin cancer cells when exposed to MK-801. It appears that a few specific and upregulated d-amino acids can reverse the drug-induced antiproliferative effect in skin cancer cells via the reactivation of NMDA receptors. This study provides a possible innovative anticancer therapy by acting on the d-amino acid pathway in cancer cells either blocking or activating their regulatory enzymes. [ABSTRACT FROM AUTHOR]

α-Amino acids are present in two opposite configurations due to the presence of a central carbon atom which is a chiral center. While l-amino acids are present in large amount in nature, only tiny quantities of their d-enantiomers exist. For a long time, d-amino acids have been considered of bacterial origin only, but recently we realized that they are present in all living organisms: notably, d-amino acids play specific and relevant functions in the different organisms. Detection and quantification of d-amino acids are mandatory to shed light on their physiological roles, especially related to foods and human health. Chromatographic techniques are among the most commonly used analytical methods for the enantioseparation of amino acids. Here, we revised the latest improvements in chromatographic direct methodologies based on chiral selectors and aimed to improve analytical speed, sensitivity, robustness, and reproducibility. While current methods are well suited for d-amino acid analysis in foodstuffs and pharmaceuticals, further improvements seem required for their simultaneous, fast and sensitive detection in biological fluids, an emerging field since d-amino acids have been proposed as biomarkers of different and relevant human pathologic states. [ABSTRACT FROM AUTHOR]

d-Amino acids are the recently detected enantiomers of l-amino acids. Accumulating evidence points their potential in solving the long-standing critical problems associated with the management of both chronic and acute kidney diseases. This includes estimating kidney function, early diagnosis and prognosis of chronic kidney disease, and disease monitoring. Among the d-amino acids, d-serine levels in the blood are strongly correlated with the glomerular filtration rate and are useful for estimating the function of the kidney. Urinary d-serine also reflects other conditions. The kidney proximal tubule reabsorbs serine with chiral-selectivity, with d-serine being reabsorbed much less efficiently than l-serine, and urinary excretion of d-serine is sensitive to the presence of kidney diseases. Therefore, assessing the intra-body dynamics of d-serine by measuring its level in blood and urinary excretion can be used to detect kidney diseases and assess pathophysiology. This new concept, the intra-body dynamics of d-serine, can be useful in the comprehensive management of kidney disease. [ABSTRACT FROM AUTHOR]

L-phenylglycine (L-Phg) is a rare non-proteinogenic amino acid, which only occurs in some natural compounds, such as the streptogramin antibiotics pristinamycin I and virginiamycin S or the bicyclic peptide antibiotic dityromycin. Industrially, more interesting than L-Phg is the enantiomeric D-Phg as it plays an important role in the fine chemical industry, where it is used as a precursor for the production of semisynthetic β-lactam antibiotics. Based on the natural L-Phg operon from Streptomyces pristinaespiralis and the stereo-inverting aminotransferase gene hpgAT from Pseudomonas putida, an artificial D-Phg operon was constructed. The natural L-Phg operon, as well as the artificial D-Phg operon, was heterologously expressed in different actinomycetal host strains, which led to the successful production of Phg. By rational genetic engineering of the optimal producer strains S. pristinaespiralis and Streptomyces lividans, Phg production could be improved significantly. Here, we report on the development of a synthetic biology-derived D-Phg pathway and the optimization of fermentative Phg production in actinomycetes by genetic engineering approaches. Our data illustrate a promising alternative for the production of Phgs. [ABSTRACT FROM AUTHOR]

The free d-amino acid, d-aspartate, is abundant in the embryonic brain but significantly decreases after birth. Besides its intracellular occurrence, d-aspartate is also present at extracellular level and acts as an endogenous agonist for NMDA and mGlu5 receptors. These findings suggest that d-aspartate is a candidate signaling molecule involved in neural development, influencing brain morphology and behaviors at adulthood. To address this issue, we generated a knockin mouse model in which the enzyme regulating d-aspartate catabolism, d-aspartate oxidase (DDO), is expressed starting from the zygotic stage, to enable the removal of d-aspartate in prenatal and postnatal life. In line with our strategy, we found a severe depletion of cerebral d-aspartate levels (up to 95%), since the early stages of mouse prenatal life. Despite the loss of d-aspartate content, Ddo knockin mice are viable, fertile, and show normal gross brain morphology at adulthood. Interestingly, early d-aspartate depletion is associated with a selective increase in the number of parvalbumin-positive interneurons in the prefrontal cortex and also with improved memory performance in Ddo knockin mice. In conclusion, the present data indicate for the first time a biological significance of precocious d-aspartate in regulating mouse brain formation and function at adulthood. [ABSTRACT FROM AUTHOR]

With the only exception of glycine, all amino acids exist in two specular structures which are mirror images of each other, called D-(dextro) and L-(levo) enantiomers. During evolution, L-amino acids were preferred for protein synthesis and main metabolism; however, the D-amino acids (D-AAs) acquired different and specific functions in different organisms (from playing a structural role in the peptidoglycan of the bacterial cell wall to modulating neurotransmission in mammalian brain). With the advent of sophisticated and sensitive analytical techniques, it was established during the past few decades that many foods contain considerable amounts of D-AAs: we consume more than 100 mg of D-AAs every day. D-AAs are present in a variety of foodstuffs, where they fulfill a relevant role in producing differences in taste and flavor and in their antimicrobial and antiaging properties from the corresponding L-enantiomers. In this review, we report on the derivation of D-AAs in foods, mainly originating from the starting materials, fermentation processes, racemization during food processing, or contamination. We then focus on leading-edge methods to identify and quantify D-AAs in foods. Finally, current knowledge concerning the effect of D-AAs on the nutritional state and human health is summarized, highlighting some positive and negative effects. Notwithstanding recent progress in D-AA research, the relationships between presence and nutritional value of D-AAs in foods represent a main scientific issue with interesting economic impact in the near future. [ABSTRACT FROM AUTHOR]

D-Amino acids are pharmaceutically important building blocks, leading to a great deal of research efforts to develop cost-effective synthetic methods. Preparation of D-amino acids by deracemization has been conceptually attractive owing to facile synthesis of racemic amino acids by Strecker synthesis. Here, we demonstrated biocatalytic deracemization of aliphatic amino acids into D-enantiomers by running cascade reactions; (1) stereoinversion of L-amino acid to a D-form by amino acid dehydrogenase and ω-transaminase and (2) regeneration of NAD+ by NADH oxidase. Under the cascade reaction conditions containing 100 mM isopropylamine and 1 mM NAD+, complete deracemization of 100 mM DL-alanine was achieved after 24 h with 95% reaction yield of D-alanine (> 99% eeD, 52% isolation yield).Graphical Abstract: [ABSTRACT FROM AUTHOR]

An active d-hydantoinase from Pseudomonas fluorescens was heterogeneously overexpressed in Escherichia coli BL21(DE3) and designated as d- PfHYD. Sequence and consensus analysis suggests that d- PfHYD belongs to the dihydropyrimidinase/hydantoinase family and possesses catalytic residues for metal ion and hydantoin binding. d- PfHYD was purified to homogeneity by nickel affinity chromatography for characterization. d- PfHYD is a homotetramer with molecular weight of 215 kDa and specific activity of 20.9 U mg. d- PfHYD showed the highest activity at pH 9.0 and 60 °C. Metal ions such as Mn, Fe, and Fe could activate d- PfHYD with 20 % improvement. Substrate specificity analysis revealed that purified d- PfHYD preferred aliphatic to aromatic 5′-monosubstituted hydantoins. Among various strategies tested, chaperone GroES-GroEL was efficient in improving the soluble expression of d- PfHYD. Employing 1.0 g L recombinant E. coli BL21(DE3)-pET28- hyd/pGRO7 dry cells, 100 mM isobutyl hydantoin was converted into d-isoleucine with 98.7 % enantiomeric excess ( ee), isolation yield of 78.3 %, and substrate to biocatalyst ratio of 15.6. Our results suggest that recombinant d- PfHYD could be potentially applied in the synthesis of d-amino acids. [ABSTRACT FROM AUTHOR]

d-Amino acids are increasingly being recognized as important signaling molecules, and abnormal levels of d-amino acids have been implicated in the pathogenesis of Alzheimer's disease. To evaluate the potential relationship between Alzheimer's disease and d-amino acids, a simple, sensitive, and reliable UPLC-MS/MS method with pre-column derivatization was developed and validated for simultaneous determination of 18 d-amino acids in rat plasma. The analytes were extracted from plasma samples by a protein precipitation procedure, and then derivatized with ( S)- N-(4-nitrophenoxycarbonyl) phenylalanine methoxyethyl ester [( S)-NIFE]. Chromatographic separation was achieved using an ACQUITY UPLC BEH C column (2.1 mm × 50 mm, 1.7 μm) with a mobile phase composed of acetonitrile containing 8 mM ammonium hydrogen carbonate at a flow rate of 0.6 mL min. The analytes were detected by electrospray ionization in positive ion multiple reaction monitoring modes. Under the optimum experimental conditions, all the linear regressions were acquired with r > 0.9932. The limits of quantitation of all derivatized d-amino acids were within 0.05-40.0 ng mL in rat plasma. The intra- and inter-day precisions, expressed as percentage relative standard deviations (%RSD), were within the range of 12.3 and 10.1 %, respectively. The recoveries for all the analytes were observed over the range of 82.8-100.5 % with RSD values less than 12.5 %. Finally, the proposed method was successfully applied to simultaneous determination of the 18 d-amino acids in plasma from Alzheimer's disease rats and age-matched normal controls. Results showed that the concentrations of d-serine, d-aspartate, d-alanine, d-leucine, and d-proline in Alzheimer's disease rat plasma were significantly decreased compared with those in normal controls, while d-phenylalanine levels increased. It was revealed that some of these d-amino acids would be potential diagnostic biomarkers for Alzheimer's disease. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

d-Amino acids exist widely in microbes, plants, animals, and food and can be applied in pharmaceutical, food, and cosmetics. Because of their widespread applications in industry, d-amino acids have recently received more and more attention. Enzymes including d-hydantoinase, N-acyl- d-amino acid amidohydrolase, d-amino acid amidase, d-aminopeptidase, d-peptidase, l-amino acid oxidase, d-amino acid aminotransferase, and d-amino acid dehydrogenase can be used for d-amino acids synthesis by kinetic resolution or asymmetric amination. In this review, the distribution, industrial applications, and enzymatic synthesis methods are summarized. And, among all the current enzymatic methods, d-amino acid dehydrogenase method not only produces d-amino acid by a one-step reaction but also takes environment and atom economics into consideration; therefore, it is deserved to be paid more attention. [ABSTRACT FROM AUTHOR]

The researches on d-hydantoinase activity and substrate specificity towards dihydropyrimidine and hydantoin derivatives have been carried out intensively over the last few decades. So far, the major efforts have focused on ( R, S)-5-phenylhydantoin and ( R, S)-5-(4-hydroxyphenyl)hydantoin, the most desirable d-hydantoinase substrates from pharmaceutical industry point of view. However, it was shown that d-hydantoinase is a substrate-dependent enzyme, and its activity and stereoselectivity towards 5-monosubstituted hydantoins varied significantly with the type of substrate and the source of the enzyme. The aim of this study was to estimate the substrate specificity of d-hydantoinase towards series of 5-benzylhydantoin derivatives with halogen and methyl substituents in the phenyl ring. The biotransformations were carried out by using commercial enzyme: immobilized, recombinant, cloned, and expressed in Escherichia coli d-hydantoinase from Vigna angularis ( rD-HYD). All reactions were monitored by capillary electrophoresis (CE), and the conversion yields were calculated. Additionally, enantiomeric ratios of the obtained d-phenylalanine derivatives were estimated by chiral high-performance liquid chromatography (HPLC). Interestingly, the differences in the activities of examined enzyme towards particular 5-benzylhydantoin derivatives were observed. CE was also shown as a promising method for monitoring the hydrolysis of new substrates by d-hydantoinase and further analyzing of enzyme substrate specificity. [ABSTRACT FROM AUTHOR]

Whereas an abundance of literature is available on the occurrence of common proteinogenic amino acids (AAs) in edible fruits of the date palm ( Phoenix dactylifera L.), recent reports on non-proteinogenic (non-coded) AAs and amino components are scarce. With emphasis on these components we have analyzed total hydrolysates of twelve cultivars of date fruits using automated ion-exchange chromatography, HPLC employing a fluorescent aminoquinolyl label, and GC-MS of total hydrolysates using the chiral stationary phases Chirasil-L-Val and Lipodex E. Besides common proteinogenic AAs, relatively large amounts of the following non-proteinogenic amino acids were detected: (2 S,5 R)-5-hydroxypipecolic acid (1.4-4.0 g/kg dry matter, DM), 1-aminocyclopropane-1-carboxylic acid (1.3-2.6 g/kg DM), γ-amino- n-butyric acid (0.5-1.2 g/kg DM), (2 S,4 R)-4-hydroxyproline (130-230 mg/kg DM), l-pipecolic acid (40-140 mg/kg DM), and 2-aminoethanol (40-160 mg/kg DM) as well as low or trace amounts (<70 mg/kg DM) of l-ornithine, 5-hydroxylysine, β-alanine, and in some samples (<20 mg/kg DM) of ( S)-β-amino isobutyric acid and (<10 mg/kg DM) l- allo-isoleucine. In one date fruit, traces of α-aminoadipic acid could be determined. Enantiomeric analysis of 6 M DCl/DO hydrolysates of AAs using chiral capillary gas chromatography-mass spectrometry revealed the presence of very low amounts of d-Ala, d-Asp, d-Glu, d-Ser and d-Phe (1.2-0.4 %, relative to the corresponding l-enantiomers), besides traces (0.2-1 %) of other d-AAs. The possible relevance of non-proteinogenic amino acids in date fruits is briefly addressed. [ABSTRACT FROM AUTHOR]

Recent work has shed light on the abundance and diversity of d-amino acids in bacterial extracellular/periplasmic molecules, bacterial cell culture, and bacteria-rich environments. Within the extracellular/periplasmic space, d-amino acids are necessary components of peptidoglycan, and disruption of their synthesis leads to cell death. As such, enzymes responsible for d-amino acid synthesis are promising targets for antibacterial compounds. Further, bacteria are shown to incorporate a diverse collection of d-amino acids into their peptidoglycan, and differences in d-amino acid incorporation may occur in response to differences in growth conditions. Certain d-amino acids can accumulate to millimolar levels in cell culture, and their synthesis is proposed to foretell movement from exponential growth phase into stationary phase. While enzymes responsible for synthesis of d-amino acids necessary for peptidoglycan ( d-alanine and d-glutamate) have been characterized from a number of different bacteria, the d-amino acid synthesis enzymes characterized to date cannot account for the diversity of d-amino acids identified in bacteria or bacteria-rich environments. Free d-amino acids are synthesized by racemization or epimerization at the α-carbon of the corresponding l-amino acid by amino acid racemase or amino acid epimerase enzymes. Additionally, d-amino acids can be synthesized by stereospecific amination of α-ketoacids. Below, we review the roles of d-amino acids in bacterial physiology and biotechnology, and we describe the known mechanisms by which they are synthesized by bacteria. [ABSTRACT FROM AUTHOR]

Primary tumors often give rise to disseminated tumor cells (DTC's), which acquire full malignancy after invading distant site(s). Thus, DTC's may be a productive target for preventing prostate cancer metastasis progression. Our prior research showed that PHSCN peptide (Ac-PHSCN-NH) targets activated α5β1 integrin to prevent invasion and metastasis in preclinical adenocarcinoma models, and disease progression in Phase I clinical trial. Here, we report that d-stereoisomer replacement of histidine and cysteine in PHSCN produces a highly potent derivative, Ac-PhScN-NH (PhScN). PhScN was 27,000- to 150,000-fold more potent as an inhibitor of basement membrane invasion by DU 145 and PC-3 prostate cancer cells. A large increase in invasion-inhibitory potency occurred after covalent modification of the sulfhydryl group in PHSCN to prevent disulfide bond formation; while the potency of covalently modified PhScN was not significantly increased. Thus PhScN and PHSCN invasion inhibition occurs by a noncovalent mechanism. These peptides also displayed similar cell surface binding dissociation constants (K), and competed for the same site. Consistent with its increased invasion-inhibitory potency, PhScN was also a highly potent inhibitor of lung extravasation and colonization in athymic nude mice: it was several hundred- or several thousand-fold more potent than PHSCN at blocking extravasation by PC-3 or DU 145 cells, and 111,000- or 379,000-fold more potent at inhibiting lung colonization, respectively. Furthermore, systemic 5 mg/kg PhScN monotherapy was sufficient to cause complete regression of established, intramuscular DU 145 tumors. PhScN thus represents a potent new family of therapeutic agents targeting metastasis by DTC's to prevent parallel progression in prostate cancer. [ABSTRACT FROM AUTHOR]

Purpose: A fundamental approach incorporating current theoretical models into aerosol formulation design potentially reduces experimental work for complex formulations. A D-amino acid mixture containing D-Leucine (D-Leu), D-Methionine, D-Tryptophan, and D-Tyrosine was selected as a model formulation for this approach. Methods: Formulation design targets were set, with the aim of producing a highly dispersible D-amino acid aerosol. Particle formation theory and a spray dryer process model were applied with boundary conditions to the design targets, resulting in a priori predictions of particle morphology and necessary spray dryer process parameters. Two formulations containing 60% w/w trehalose, 30% w/w D-Leu, and 10% w/w remaining D-amino acids were manufactured. Results: The design targets were met. The formulations had rugose and hollow particles, caused by deformation of a crystalline D-Leu shell while trehalose remained amorphous, as predicted by particle formation theory. D-Leu acts as a dispersibility enhancer, ensuring that both formulations: 1) delivered over 40% of the loaded dose into the in vitro lung region, and 2) achieved desired values of lung airway surface liquid concentrations based on lung deposition simulations. Conclusions: Theoretical models were applied to successfully achieve complex formulations with design challenges a priori. No further iterations to the design process were required. [ABSTRACT FROM AUTHOR]

d-Kynurenine ( d-KYN), a metabolite of d-tryptophan, can serve as the bioprecursor of kynurenic acid (KYNA) and 3-hydroxykynurenine, two neuroactive compounds that are believed to play a role in the pathophysiology of several neurological and psychiatric diseases. In order to investigate the possible presence of d-KYN in biological tissues, we developed a novel assay based on the conversion of d-KYN to KYNA by purified d-amino acid oxidase ( d-AAO). Samples were incubated with d-AAO under optimal conditions for measuring d-AAO activity (100 mM borate buffer, pH 9.0), and newly produced KYNA was detected by high-performance liquid chromatography (HPLC) with fluorimetric detection. The detection limit for d-KYN was 300 fmol, and linearity of the assay was ascertained up to 300 pmol. No assay interference was noted when other d-amino acids, including d-serine and d-aspartate, were present in the incubation mixture at 50-fold higher concentrations than d-KYN. Using this new method, d-KYN was readily detected in the brain, liver, and plasma of mice treated systemically with d-KYN (300 mg/kg). In these experiments, enantioselectivity was confirmed by determining total kynurenine levels in the same samples using a conventional HPLC assay. Availability of a sensitive, specific, and simple method for d-KYN measurement will be instrumental for evaluating whether d-KYN should be considered for a role in physiology and pathology. [ABSTRACT FROM AUTHOR]

Genetic, biochemical, and pathological evidence supports that aggregation of amyloid-beta (Aβ) peptide into fibrillar structures rich in beta-sheets is implicated as the cause of Alzheimer's disease. Therefore, an attractive therapeutic strategy is to prevent or alter amyloid-beta aggregation. In this work we examine the effects of the short d-peptides pgklvya, kklvffarrrra, and kklvffa on Aβ aggregation in vitro and toxicity in vivo. These peptides are based on the central hydrophobic region of Aβ (residues 16-20), which is believed to be crucial in Aβ self-association. The effect of peptides on Aβ aggregation was examined by circular dichroism spectroscopy, Thioflavin T fluorescence, and ANS binding assay. Transgenic Caenorhabditis elegans model was used to evaluate the pharmacological effect of d-peptides on Aβ-initiated toxicity. The data suggested that d-peptides are very effective at inhibiting fibrillogenesis of Aβ. Among the three peptides tested, only pgklvya and kklvffa improved survival in the transgenic C. elegans. The activity of these peptides correlates with their ability to inhibit Aβ oligomerization. These suggest that d-peptides should be considered during future design of peptide-based inhibitors of amyloid deposition and toxicity. [ABSTRACT FROM AUTHOR]

Free d-aspartate ( d-Asp) occurs in substantial amounts in the brain at the embryonic phase and in the first few postnatal days, and strongly decreases in adulthood. Temporal reduction of d-Asp levels depends on the postnatal onset of d-aspartate oxidase (DDO) activity, the only enzyme able to selectively degrade this d-amino acid. Several results indicate that d-Asp binds and activates N-methyl- d-aspartate receptors (NMDARs). Accordingly, recent studies have demonstrated that deregulated, higher levels of d-Asp, in knockout mice for Ddo gene and in d-Asp-treated mice, modulate hippocampal NMDAR-dependent long-term potentiation (LTP) and spatial memory. Moreover, similarly to d-serine, administration of d-Asp to old mice is able to rescue the physiological age-related decay of hippocampal LTP. In agreement with a neuromodulatory action of d-Asp on NMDARs, increased levels of this d-amino acid completely suppress long-term depression at corticostriatal synapses and attenuate the prepulse inhibition deficits produced in mice by the psychotomimetic drugs, amphetamine and MK-801. Based on the evidence which points to the ability of d-Asp to act as an endogenous agonist on NMDARs and considering the abundance of d-Asp during prenatal and early life, future studies will be crucial to address the effect of this molecule in the developmental processes of the brain controlled by the activation of NMDARs. [ABSTRACT FROM AUTHOR]

d-Aspartate ( d-Asp) is an endogenous amino acid in the central nervous and reproductive systems of vertebrates and invertebrates. High concentrations of d-Asp are found in distinct anatomical locations, suggesting that it has specific physiological roles in animals. Many of the characteristics of d-Asp have been documented, including its tissue and cellular distribution, formation and degradation, as well as the responses elicited by d-Asp application. d-Asp performs important roles related to nervous system development and hormone regulation; in addition, it appears to act as a cell-to-cell signaling molecule. Recent studies have shown that d-Asp fulfills many, if not all, of the definitions of a classical neurotransmitter-that the molecule's biosynthesis, degradation, uptake, and release take place within the presynaptic neuron, and that it triggers a response in the postsynaptic neuron after its release. Accumulating evidence suggests that these criteria are met by a heterogeneous distribution of enzymes for d-Asp's biosynthesis and degradation, an appropriate uptake mechanism, localization within synaptic vesicles, and a postsynaptic response via an ionotropic receptor. Although d-Asp receptors remain to be characterized, the postsynaptic response of d-Asp has been studied and several l-glutamate receptors are known to respond to d-Asp. In this review, we discuss the current status of research on d-Asp in neuronal and neuroendocrine systems, and highlight results that support d-Asp's role as a signaling molecule. [ABSTRACT FROM AUTHOR]

Analogs of the H-Tyr-Asp-Pro-Ala-Pro-OH pentapeptide with d-amino acid residues either in differing or in all of the positions of the sequences were prepared and their oostatic potency was compared with that of the parent pentapeptide. The d-amino acid residue containing analogs exhibited an equal or even higher oostatic effect in the flesh fly Neobellieria bullata than the parent peptide. Contrary to the rapid incorporation of radioactivity from the labeled H-Tyr-Asp-[H]Pro-Ala-Pro-OH pentapeptide into the ovaries of N. bullata in vitro, the radioactivity incorporation from the labeled pentapeptides with either d-aspartic acid or d-alanine was significantly delayed. As compared to the parent pentapeptide, also the degradation of both the d-amino acid-containing analogs mentioned above proceeded at a significantly lower rate. The decreased intake of radioactivity, the lower degradation and finally also the high oostatic effect may be ascribed to the decreased enzymatic degradation of the peptide bonds neighboring the d-amino acid residues in the corresponding peptides. The introduction of the non-coded d-amino acids thus enhances the oostatic effect in N. bullata owing to the prolonged half-life of the corresponding pentapeptides, which can thus affect more ovarian cells. [ABSTRACT FROM AUTHOR]

This paper reviews and interprets a method for determining the nutritional value of d-amino acids, d-peptides, and amino acid derivatives using a growth assay in mice fed a synthetic all-amino acid diet. A large number of experiments were carried out in which a molar equivalent of the test compound replaced a nutritionally essential amino acid such as l-lysine ( l-Lys), l-methionine ( l-Met), l-phenylalanine ( l-Phe), and l-tryptophan ( l-Trp) as well as the semi-essential amino acids l-cysteine ( l-Cys) and l-tyrosine ( l-Tyr). The results show wide-ranging variations in the biological utilization of test substances. The method is generally applicable to the determination of the biological utilization and safety of any amino acid derivative as a potential nutritional source of the corresponding l-amino acid. Because the organism is forced to use the d-amino acid or amino acid derivative as the sole source of the essential or semi-essential amino acid being replaced, and because a free amino acid diet allows better control of composition, the use of all-amino-acid diets for such determinations may be preferable to protein-based diets. Also covered are brief summaries of the widely scattered literature on dietary and pharmacological aspects of 27 individual d-amino acids, d-peptides, and isomeric amino acid derivatives and suggested research needs in each of these areas. The described results provide a valuable record and resource for further progress on the multifaceted aspects of d-amino acids in food and biological samples. [ABSTRACT FROM AUTHOR]

Biofilms of sulfate reducing bacteria (SRB) are often responsible for Microbiologically Influenced Corrosion (MIC) that is a major problem in the oil and gas industry as well as water utilities and other industries. This work was inspired by recent reports that some d-amino acids may be useful in the control of microbial biofilms. A d-amino acid mixture with equimolar d-tyrosine, d-methionine, d-tryptophan and d-leucine was tested in this work for their enhancement of a biocide cocktail containing tetrakis (hydroxymethyl) phosphonium sulfate (THPS) and ethylenediamine- N, N'-disuccinic acid (EDDS). Desulfovibrio vulgaris (ATCC 7757) was cultured in ATCC 1249 medium. Its biofilm was grown on C1018 carbon steel coupons. Experimental results indicated that the triple biocide cocktail consisting of 30 ppm THPS, 500 ppm EDDS and 6.6 ppm d-amino acid mixture (with equimolar d-tyrosine, d-methionine, d-tryptophan and d-leucine) was far more effective than THPS and EDDS alone and their binary combination. The triple biocide cocktail effectively prevented SRB biofilm establishment and removed the established SRB biofilm. The d-amino acid mixture alone did not show significant effects in the two tasks even at 660 ppm. [ABSTRACT FROM AUTHOR]

Free l- and d-amino acids were determined by chiral GC-MS in 26 wines, comprising white wines, red wines, ice wines and sparkling wines. The aim of the work was to investigate whether quantities and pattern of d-amino acids, in particular d-proline, correlate with the storage time of bottled wines. The relative quantities with respect to the corresponding l-enantiomer ranged in white wines from 0.4 to 3.9% d-Ala, 0.9–8.3% d-Asx, and 0.5–8.9% d-Glx, in red wines from 2.9 to 10.6% d-Ala, 2.2–10.9% d-Asx, and 3.9–7.4% d-Glx, and in sparkling wines from 2.2 to 9.8% d-Ala, 2.1–4.4% d-Asx and 1.3–6.1% d-Glx. Low relative quantities of 0.3–0.7% d-Pro were detected in three white wines stored for more than 20 years and did not exceed 0.2% d-Pro in two red wines stored for 10 and 20 years, respectively. An ice wine stored for 24 years contained 0.9% d-Pro, 6.4% d-Glx, 3.0% d-Asp and 1.5% d-Ala. The data confirm the presence of d-amino acids in wines. They do not provide evidence for a correlation between the storage time of bottled wines and quantities of d-amino acids. [ABSTRACT FROM AUTHOR]

D-Amino acid oxidase (DAAO) is an FAD-dependent enzyme that metabolizes D-amino acids in microbes and animals. However, such ability has not been identified in plants so far. We predicted a complete DAAO coding sequence consisting of 1158 bp and encoding a protein of 386 amino acids. We cloned this sequence from the leaf cDNA population of maize plants that could utilize D-alanine as a nitrogen source and grow normally on media containing D-Ala at the concentrations of 100 and 1000 ppm. For more understanding of DAAO ability in maize plant, we produced a recombinant plasmid by the insertion of isolated cDNA into the pMALc2X Escherichia coli expression vector, downstream of the maltose-binding protein coding sequence. The pMALc2X-DAAO vector was used to transform the TB1 strain of E. coli cells. Under normal growth conditions, fused DAAO (with molecular weight of about 78 kDa) was expressed up to 5 mg/liter of bacterial cells. The expressed product was purified by affinity chromatography and subjected to in vitro DAAO activity assay in the presence of five different D-amino acids. Fused DAAO could oxidize D-alanine and D-aspartate, but not D-leucine, D-isoleucine, and D-serine. The cDNA sequence reported in this paper has been submitted to EMBL databases under accession number AM407717. [ABSTRACT FROM AUTHOR]

D-Amino acid oxidase (DAAO) is a FAD-containing flavoenzyme that catalyzes the oxidative deamination of D-isomers of neutral and polar amino acids. This enzymatic activity has been identified in most eukaryotic organisms, the only exception being plants. In the various organisms in which it does occur, DAAO fulfills distinct physiological functions: from a catabolic role in yeast cells, which allows them to grow on D-amino acids as carbon and energy sources, to a regulatory role in the human brain, where it controls the levels of the neuromodulator D-serine. Since 1935, DAAO has been the object of an astonishing number of investigations and has become a model for the dehydrogenase-oxidase class of flavoproteins. Structural and functional studies have suggested that specific physiological functions are implemented through the use of different structural elements that control access to the active site and substrate/product exchange. Current research is attempting to delineate the regulation of DAAO functions in the contest of complex biochemical and physiological networks. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the properties of the D-amino acid isomers O-18F-fluoromethyl tyrosine (18F-FMT), O-18F-fluoroethyl tyrosine (18F-FET) and O-18F-fluoropropyl tyrosine (18F-FPT) as tumour-detecting agents with PET in comparison with the corresponding L-isomers. L- or D-18F-FMT, 18F-FET or 18F-FPT, prepared by 18F-fluoromethylation, 18F-fluoroethylation or 18F-fluoropropylation of L- and D-tyrosine, was intravenously injected into BALB/cA Jcl- nu mice bearing HeLa tumour cells. At 5, 15, 30 and 60 min post intravenous administration, the uptake of each compound in normal abdominal organs and xenotransplanted HeLa cells was determined using the tissue dissection method. Metabolic stability analyses of these compounds in the plasma were performed with the thin-layer chromatography method. In the plasma fraction, although L- and D-isomers of 18F-FMT, 18F-FET and 18F-FPT provided comparable metabolic stability, D-isomers of these labelled compounds revealed a faster elimination rate than their L-isomers, with a higher peak uptake in the blood and kidney 5 min post administration. Compared with natural amino acid ligands, such as L-11C-methionine, the uptake of L-isomers of these labelled compounds was relatively low and stable in the abdominal organs, while D-isomers revealed much lower and faster clearance rates compared with the corresponding L-isomers. Among the abdominal organs, the pancreas showed relatively high uptake of all the labelled compounds used here, and the uptake of D-isomers was much lower than that of the L-isomers. Although tumour uptake levels of D-isomers of 18F-FMT, 18F-FET and 18F-FPT were almost 95%, 43% and 39% of the uptake levels of each of the L-isomers 60 min post administration, the tumour-to-blood ratios of these D-isomers were 181%, 137% and 101% of the ratios of the corresponding L-isomers. D-isomers of 18F-FMT and 18F-FET indicated improved tumour-to-liver ratios compared with the corresponding L-isomers, and D-18F-FPT showed the highest tumour-to-pancreas ratio among all the other compounds assayed here. These results suggest that D-isomers of 18F-fluoroalkyl tyrosine analogues are potential tracers for tumour imaging with PET. [ABSTRACT FROM AUTHOR]

Saccharomyces cerevisiae is sensitive to d-amino acids: those corresponding to almost all proteinous l-amino acids inhibit the growth of yeast even at low concentrations (e.g. 0.1 mM). We have determined that d-amino acid- N-acetyltransferase (DNT) of the yeast is involved in the detoxification of d-amino acids on the basis of the following findings. When the DNT gene was disrupted, the resulting mutant was far less tolerant to d-amino acids than the wild type. However, when the gene was overexpressed with a vector plasmid p426Gal1 in the wild type or the mutant S. cerevisiae as a host, the recombinant yeast, which was found to show more than 100 times higher DNT activity than the wild type, was much more tolerant to d-amino acids than the wild type. We further confirmed that, upon cultivation with d-phenylalanine, N-acetyl- d-phenylalanine was accumulated in the culture but not in the wild type and hpa3Δ cells overproducing DNT cells. Thus, d-amino acids are toxic to S. cerevisiae but are detoxified with DNT by N-acetylation preceding removal from yeast cells. [ABSTRACT FROM AUTHOR]

The venoms of predatory cone snails (genus Conus) have yielded a complex library of about 50–100,000 bioactive peptides, each believed to have a specific physiological target (although peptides from different species may overlap in their target specificity). Conus has evolved the equivalent of a drug development strategy that combines the accelerated evolution of toxin sequences with an unprecedented degree of posttranslational modification. Some Conus venom peptide families are the most highly posttranslationally modified classes of gene products known. We review the variety and complexity of posttranslational modifications documented in Conus peptides so far, and explore the potential of Conus venom peptides as a model system for a more general understanding of which secreted gene products may have modified amino acids. Although the database of modified conotoxins is growing rapidly, there are far more questions raised than answers provided about possible mechanisms and functions of posttranslational modifications in Conus. [ABSTRACT FROM AUTHOR]

An overview of the use of non-protein amino acids in the design of conformationally well-defined peptides, based on work from the author's laboratory, is discussed. The crystal structures of several designed oligopeptides illustrate the use α-aminoisobutyric acid (Aib) in the construction of helices, D-amino acids in the design of helix termination segments andPro-Xxx segments for nucleating of β-hairpin structures. β- and γ-amino acid residues have been used to expand the range of designed polypeptide structures. [ABSTRACT FROM AUTHOR]

-AAs in 6 M HCl at 100°C. The rate of isomerization on heating in vinegar and aqueous AcOH was aspartic acid (Asp)>serine (Ser)≫proline (Pro), whereas in 6 M HCl it was Asp>Pro≫Ser. Heating of L-Pro together with glucose and fructose in 5% AcOH at 100°C for 96 h led to the formation of 24% D-Pro relative to L-Pro. From the data it is concluded that high relative amounts of D-Pro detected in matured vinegars are not attributable to acid-catalyzed racemization. In balsamic vinegars high relative amounts of D-Pro are mainly attributed to the Maillard reaction. [ABSTRACT FROM AUTHOR]

Urine of ddY/DAO mice lacking d-amino-acid oxidase contained 5.7 times more serine than that of normal ddY/DAO+ mice. Most of the serine was d-isomer. The origin of thisd-serine was examined. Oral administration of 0.02% amoxicillin and 0.004% minocycline to the ddY/ DAO- mice for 7 days did not reduce the urinary d-serine, indicating that the d-serine was not of intestinal bacterial origin. When the mouse diet was changed to one with different compositions, the urinary d-serine was considerably reduced. Furthermore, starvation of the ddY/DAO- mice for 24 hours reduced the urinary d-serine to 33% of the original level. These results indicate that most of the urinary d-serine comes from the diet. However, the urine of the starved ddY/DAO- mice still contained 4.6 times more d-serine than that of the ddY/DAO+ mice, suggesting a part of the D-serine have an endogenous origin. [ABSTRACT FROM AUTHOR]

A series of peptides based on D-amino-acids, and with an N-terminal D-phenylalanine residue, was synthesised by solution methods using t-butoxycarbonyl amino protection. These peptides were designed to resist metabolism in the gastrointestinal tract and to serve as probes of the effects of molecular shape and charge on the paracellular route of drug uptake in the gut. The peptides were characterised by NMR spectroscopy, FAB mass spectrometry, optical rotation and purified by HPLC. [ABSTRACT FROM AUTHOR]

A method has been developed to determine the age of fossil bone samples based on amino acid racemization (AAR). Approximately one hundred fossil bone samples of known age from Hungary were collected and analysed for D- and L-amino acids. As the racemization of amino acids is affected by temperature, pH, metal content of the soil, and time passed since death, these factors were eliminated by comparing the estimated age to age determined by the radiocarbon method. Determining the D- and L-amino acid contents in samples of known age, determining the half life of racemization and plotting the D/L ratio as a function of time, calibration curves were obtained. These curves can be used for the age estimation of samples after determining their D- and L-amino acid content. The D/L ratio for 2 to 3 amino acids was determined for each sample and the mean value of estimated ages based on calibration curves was considered to estimate age of the fossil samples. [ABSTRACT FROM AUTHOR]

Total D-amino acids were measured in plasma for 20 non-dialysed patients (creatinine clearance < 12 ml/minute), 20 on CAPD, 20 on haemodialysis and 20 normals. Plasma D-tyrosine and D-phenylalanine were measured in 8 of each group by HPLC. Total D-amino acids, D-tyrosine and D-phenylalanine were significantly greater for patients than normals. D-amino acids and D-tyrosine correlated with creatinine and were decreased during HD. During dialysis, the mean losses for D-tyrosine and D-phenylalanine were similar, about 0.2 mg/CAPD exchange and 3 mg/4 hour haemodialysis (i.e. 2% of the total amino acid, as in plasma). Clearance was unaffected by stereochemical configuration. Urinary losses/24 hour in the non-dialysed patients were 0.35 mg D-tyrosine and 0.25 mg D-phenylalanine. Clearance for D-phenylalanine was greater than for the L-enantiomer. Increases in D-amino acids in renal failure are probably due to depletion of D-amino acid oxidase, but may be enhanced by a D-amino acid rich diet, peptide antibiotics and D-amino acid oxidase inhibiting drugs and metabolites. Possible toxic effects need further investigation. [ABSTRACT FROM AUTHOR]