Search

A large literature exists on the biochemistry, chemistry, metabolism, and clinical importance of the α-keto acid analogues of many amino acids. However, although glutamine is the most abundant amino acid in human tissues, and transamination of glutamine to its α-keto acid analogue (α-ketoglutaramate; KGM) was described more than seventy years ago, little information is available on the biological importance of KGM. Herein, we summarize the metabolic importance of KGM as an intermediate in the glutamine transaminase – ω-amidase (GTωA) pathway for the conversion of glutamine to anaplerotic α-ketoglutarate. We describe some properties of KGM, notably its occurrence as a lactam (2-hydroxy-5-oxoproline; 99.7% at pH 7.2), and its presence in normal tissues and body fluids. We note that the concentration of KGM is elevated in the cerebrospinal fluid of liver disease patients and that the urinary KGM/creatinine ratio is elevated in patients with an inborn error of the urea cycle and in patients with citrin deficiency. Recently, of the 607 urinary metabolites measured in a kidney disease study, KGM was noted to be one of five metabolites that was most significantly associated with uromodulin (a potential biomarker for tubular functional mass). Finally, we note that KGM is an intermediate in the breakdown of nicotine in certain organisms and is an important factor in nitrogen homeostasis in some microorganisms and plants. In conclusion, we suggest that biochemists and clinicians should consider KGM as (i) a key intermediate in nitrogen metabolism in all branches of life, and (ii) a biomarker, along with ω-amidase, in several diseases. [ABSTRACT FROM AUTHOR]

Abstract Background 1,5-pentanediol (1,5-PDO) is a linear diol with an odd number of methylene groups, which is an important raw material for polyurethane production. In recent years, the chemical methods have been predominantly employed for synthesizing 1,5-PDO. However, with the increasing emphasis on environmentally friendly production, it has been a growing interest in the biosynthesis of 1,5-PDO. Due to the limited availability of only three reported feasible biosynthesis pathways, we developed a new biosynthetic pathway to form a cell factory in Escherichia coli to produce 1,5-PDO. Results In this study, we reported an artificial pathway for the synthesis of 1,5-PDO from lysine with an integrated cofactor and co-substrate recycling and also evaluated its feasibility in E.coli. To get through the pathway, we first screened aminotransferases originated from different organisms to identify the enzyme that could successfully transfer two amines from cadaverine, and thus GabT from E. coli was characterized. It was then cascaded with lysine decarboxylase and alcohol dehydrogenase from E. coli to achieve the whole-cell production of 1,5-PDO from lysine. To improve the whole-cell activity for 1,5-PDO production, we employed a protein scaffold of EutM for GabT assembly and glutamate dehydrogenase was also validated for the recycling of NADPH and α-ketoglutaric acid (α-KG). After optimizing the cultivation and bioconversion conditions, the titer of 1,5-PDO reached 4.03 mM. Conclusion We established a novel pathway for 1,5-PDO production through two consecutive transamination reaction from cadaverine, and also integrated cofactor and co-substrate recycling system, which provided an alternative option for the biosynthesis of 1,5-PDO.

Background: 1,5-pentanediol (1,5-PDO) is a linear diol with an odd number of methylene groups, which is an important raw material for polyurethane production. In recent years, the chemical methods have been predominantly employed for synthesizing 1,5-PDO. However, with the increasing emphasis on environmentally friendly production, it has been a growing interest in the biosynthesis of 1,5-PDO. Due to the limited availability of only three reported feasible biosynthesis pathways, we developed a new biosynthetic pathway to form a cell factory in Escherichia coli to produce 1,5-PDO. Results: In this study, we reported an artificial pathway for the synthesis of 1,5-PDO from lysine with an integrated cofactor and co-substrate recycling and also evaluated its feasibility in E.coli. To get through the pathway, we first screened aminotransferases originated from different organisms to identify the enzyme that could successfully transfer two amines from cadaverine, and thus GabT from E. coli was characterized. It was then cascaded with lysine decarboxylase and alcohol dehydrogenase from E. coli to achieve the whole-cell production of 1,5-PDO from lysine. To improve the whole-cell activity for 1,5-PDO production, we employed a protein scaffold of EutM for GabT assembly and glutamate dehydrogenase was also validated for the recycling of NADPH and α-ketoglutaric acid (α-KG). After optimizing the cultivation and bioconversion conditions, the titer of 1,5-PDO reached 4.03 mM. Conclusion: We established a novel pathway for 1,5-PDO production through two consecutive transamination reaction from cadaverine, and also integrated cofactor and co-substrate recycling system, which provided an alternative option for the biosynthesis of 1,5-PDO. [ABSTRACT FROM AUTHOR]

The kinetic resolution of racemic amino acids mediated by dipeptides and pyridoxal provides a prebiotically plausible route to enantioenriched proteinogenic amino acids. The enzymatic transamination cycles that are key to modern biochemical formation of enantiopure amino acids may have evolved from this half of the reversible reaction couple. Kinetic resolution of racemic precursors emerges as a general route to enantioenrichment under prebiotic conditions. [ABSTRACT FROM AUTHOR]

Transamination reactions of two different aminosilanes (trimethyl(tert-butylamino)silane and dimethyl(diamino)silane) with amines (diethylamine, pyrrolidine, tert-butylamine, iso-propylamine, and n-propylamine) are studied. For trimethyl(organoamino)silanes, the reaction of trimethyl(iso-propylamino)- or trimethyl(diethylamino)silane as aminosilanes and aniline or pyrrolidine are good starting materials to produce trimethyl(anilino)- and trimethyl(pyrrolidino)silane. The investigated equilibrium constants of the reactions of monoaminosilanes show a good correlation with quantum chemically calculated values. The reaction of two different diaminosilanes Me2Si(NR1R2)2 and Me2Si(NR3R4)2 containing different amino moieties leads to the formation of mixed diaminosilanes Me2Si(NR1R2)(NR3R4) in most cases.

[Display omitted] N -Iodoacetyl-substituted azoles undergo transfer of iodoacetyl group from heterocyclic N atom toward the amino group of amino azoles, unlike the earlier investigated iodomethyl ketones. The proposed mechanism explaining the observed difference in such transamination is confirmed by calculations. The product derived from 2-aminobenzimidazole is cyclized into fused imidazo[1,2-α]benzimidazol- 9-ium salt. [ABSTRACT FROM AUTHOR]

New cycloalka[b]pyridine and chromene derivatives were synthesized by multicomponent con-densa-tions. The structure of some of the synthesized compounds was determined by X-ray analysis. [ABSTRACT FROM AUTHOR]

Transaminases capable of carrying out chiral selective transamination of 1-(3-methylphenyl)ethan-1-one to (1R)-(3-methylphenyl)ethan-1-amine were screened, and ATA-025 was the best enzyme, while dimethylsulfoxide (10% V/V) was the best co-solvent for said bioconversion. The variables such as enzyme loading, substrate loading, temperature, and pH for development of process displaying maximum conversion with good product formation and higher yield were optimized. The ambient processing conditions were 10% enzyme loading/50 g/L substrate loading/45 °C/pH 8.0, and 5% enzyme loading/36.78 g/L substrate loading/42.66 °C/pH 8.2 displaying maximum conversion 99.01 ± 2.47% and 96.115 ± 1.97%, and 76.93 ± 1.05% and 73.12 ± 1.04% yield with one factor at a time approach and numerical optimization with Box Behnken Design, respectively. In the final optimized reaction, ATA-025 showed the highest 99.22 ± 2.61% conversion, 49.55 g/L product formation, with an actual product recovery of 38.16 g corresponding to a product yield 77.03 ± 1.01% with respect to the product formed after reaction. The purity of recovered product (1R)-(3-methylphenyl)ethan-1-amine formed was ≥ 99% (RP-HPLC), and chiral purity ≥ 98.5% (Chiral-GC), and it was also confirmed and characterized with instrumental methods using boiling point, LC–MS, ATR-FTIR, and 1H NMR. The findings of 'What If' studies performed by investigating timely progress of reaction on gram scale by drastically changing the process parameters revealed a substantial modification in process variables to achieve desired results. (1R)-(3-methylphenyl)ethan-1-amine synthesized by green, facile and novel enzymatic approach with an optimized process could be used for synthesis of different active pharma entities. [ABSTRACT FROM AUTHOR]

An unprecedented Cinchona alkaloid catalyzed atropoenantioselective transamination of biaryl aldehydes with 2,2-diphenylglycine via a cascade decarboxylation and dynamic kinetic resolution strategy is described. This protocol features broad substrate scope and good functional group tolerance and allows the rapid assembly of axially chiral biaryls in high yields with acceptable to good enantioselectivities. In addition, such structural motifs may have potential applications in enantioselective catalysis as chiral ligands or catalysts. [ABSTRACT FROM AUTHOR]

We report a straightforward chemical strategy to tackle current challenges of irreversible deformation in low Tg vitrimers at operating temperature. In particular, vinylogous urethane (VU) vitrimers were prepared where reactive free amines, necessary for material flow, were temporarily shielded inside the network backbone, by adding a small amount of dibasic ester to the curing mixture. The amines could be released as reactive chain ends from the resulting dicarboxamide bonds via thermally reversible cyclisation to an imide moiety. Indeed, (re)generation of the required nucleophilic amines as network defects ensured reprocessing and rapid material flow at higher temperature, where exchange dynamics are (re)activated. As a result, VU vitrimers were obtained with limited creep at service temperature, yet with good reprocessability at elevated temperatures. Thus, by exerting strong control on the molecular level over the availability of exchangeable functional groups, a remarkable improvement of VU properties was obtained. [ABSTRACT FROM AUTHOR]

ω-Transaminases (ω-TAs) are attractive biocatalysts asymmetrically catalyzing ketones to chiral amines. However, poor non-native catalytic activity and substrate promiscuity severely hamper its wide application in industrial production. Protein engineering efforts have generally focused on reshaping the substrate-binding pockets of ω-TAs. However, hotspots around the substrate tunnel as well as distant sites outside the pockets may also affect its activity. In this study, the ω-TA from Bacillus megaterium (BmeTA) was selected for engineering. The tunnel mutation Y164F synergy with distant mutation A245T which was acquired through a multiple sequence alignment showed improved soluble expression, a 3.7-fold higher specific activity and a 19.9-fold longer half-life at 45 °C. Molecule Dynamics simulation explains the mechanism of improved catalytic activity, enhanced thermostability and improved soluble expression of BmeTA Y164F/A245T (2 M). Finally, the resting cells of 2 M were used for biocatalytic processes. 450 mM of S-methoxyisopropylamine (S-MOIPA) was obtained with an ee value of 97.3 % and a conversion rate of 90 %, laying the foundation for its industrial production. Mutant 2 M was also found to be more advantageous in catalyzing the transamination of various ketones. These results demonstrated that sites that are far away from the active center also play an important role in the redesign of ω-TAs., (© 2024 Wiley-VCH GmbH.)

YggS is a pyridoxal 5′‐phosphate (PLP)‐binding protein of the conserved COG0325 family. Despite a connection with vitamin B6 homeostasis in many species, neither a precise biochemical activity nor the molecular mechanism of how YggS contributes to cellular function has been described. In a transposon mutagenesis screen, we found that insertions in aspC (encoding a PLP‐dependent aspartate aminotransferase, EC 2.6.1.1) in a Salmonella enterica strain lacking yggS caused a synthetic growth defect, which could be rescued by the addition of exogenous aspartate. Characterization of spontaneous suppressors which improved the growth of the yggS aspC double mutant suggested that this synthetic aspartate limitation was dependent on TyrB, a PLP‐dependent aromatic amino acid aminotransferase (EC 2.6.1.57). Genetic and biochemical data were consistent with the hypothesis that TyrB activity was inhibited by accumulated pyridoxine 5′‐phosphate and α‐keto acids caused by a yggS mutation. This study provides data consistent with a working model implicating YggS in modulating concentrations of B6 vitamers via transamination. [ABSTRACT FROM AUTHOR]

A key aim of biocatalysis is to mimic the ability of eukaryotic cells to carry out multistep cascades in a controlled and selective way. As biocatalytic cascades get more complex, reactions become unattainable under typical batch conditions. Here a number of continuous flow systems were used to overcome batch incompatibility, thus allowing for successful biocatalytic cascades. As proof‐of‐principle, reactive carbonyl intermediates were generated in situ using alcohol oxidases, then passed directly to a series of packed‐bed modules containing different aminating biocatalysts which accordingly produced a range of structurally distinct amines. The method was expanded to employ a batch incompatible sequential amination cascade via an oxidase/transaminase/imine reductase sequence, introducing different amine reagents at each step without cross‐reactivity. The combined approaches allowed for the biocatalytic synthesis of the natural product 4O‐methylnorbelladine. [ABSTRACT FROM AUTHOR]

Lyophilized whole cells and the crude enzymatic extract from the fungus Stemphylium lycopersici were successfully immobilized in situ in rigid polyurethane foam, as an alternative biocatalyst for the kinetic resolution of rac -1-phenylethylamine, an interesting building block in the synthesis of pharmaceuticals. The enzymatic activity of immobilized whole cells and the crude enzymatic extract was 2.52 and 5.05 U/g, respectively. The immobilization yield in polyurethane of both forms was at least above 100%, and the process did not change the affinity of the biocatalyst for the substrate. The optima reaction conditions for the kinetic resolution of rac -1-phenylethylamine into acetophenone were: 32.5 °C, 120 rpm by 24 h containing 10 mL (20% m/v) of phosphate buffer (pH 7.5) and 20% biocatalyst mass, resulting in conversions of 45% and 34% using the immobilized lyophilized fungus and crude enzymatic extract, respectively. Stemphylium lycopersici was also subjected to high pressure using CO 2. The best conditions provided conversions of 49 (99% ee) and 26.21 (without ee) using the immobilized lyophilized fungus and the immobilized lyophilized crude enzyme extract, respectively, with 20 cycles of reuse and recovery greater than 50% (fungus). Interestingly, the compounds were satisfactorily converted to the corresponding ketones with up to 90% ee for the R- enantiomer. The capacity for conversion of the immobilized lyophilized fungus to different amines: rac -1,2,3,4-tetrahydro-1-naphthylamine, rac -1-phenylpropylamine, and rac -phenylbutylamine was also evaluated. ω-transaminase activity changed significantly depending on the experimental conditions applied, allowing the selection of proper operating conditions for advantageous application of this biocatalyst in transamination reactions. • Stemphylium lycopersici as biocatalyst for kinetic resolution of amines. • The efficiency of polyurethane for the immobilization of biocatalysts. • The fungal whole cell contributes positively for ω-transamination reactions. • The activation process in pressurized CO 2 provided a better catalytic performance. [ABSTRACT FROM AUTHOR]

Aim: We have reported earlier that a high salt intake triggered an aestivation‐like natriuretic‐ureotelic body water conservation response that lowered muscle mass and increased blood pressure. Here, we tested the hypothesis that a similar adaptive water conservation response occurs in experimental chronic renal failure. Methods: In four subsequent experiments in Sprague Dawley rats, we used surgical 5/6 renal mass reduction (5/6 Nx) to induce chronic renal failure. We studied solute and water excretion in 24‐hour metabolic cage experiments, chronic blood pressure by radiotelemetry, chronic metabolic adjustment in liver and skeletal muscle by metabolomics and selected enzyme activity measurements, body Na+, K+ and water by dry ashing, and acute transepidermal water loss in conjunction with skin blood flow and intra‐arterial blood pressure. Results: 5/6 Nx rats were polyuric, because their kidneys could not sufficiently concentrate the urine. Physiological adaptation to this renal water loss included mobilization of nitrogen and energy from muscle for organic osmolyte production, elevated norepinephrine and copeptin levels with reduced skin blood flow, which by means of compensation reduced their transepidermal water loss. This complex physiologic‐metabolic adjustment across multiple organs allowed the rats to stabilize their body water content despite persisting renal water loss, albeit at the expense of hypertension and catabolic mobilization of muscle protein. Conclusion: Physiological adaptation to body water loss, termed aestivation, is an evolutionary conserved survival strategy and an under‐studied research area in medical physiology, which besides hypertension and muscle mass loss in chronic renal failure may explain many otherwise unexplainable phenomena in medicine. [ABSTRACT FROM AUTHOR]

The presence of rosmarinic acid (RA) in the hornwort A. agrestis is well known, and some attempts have been made to clarify the biosynthesis of this cafeic acid ester in lower plants. Parallel to the biosynthesis in vascular plants, the involvement of tyrosine aminotransferase (EC 2.6.1.5; TAT) as the initial step was assumed. The amplifcation of a nucleotide sequence putatively encoding AaTAT (Genbank MN922307) and expression in E. coli were successful. The enzyme proved to have a high acceptance of L-tyrosine (Km 0.53 mM) whilst slightly preferring 2-oxoglutarate over phenylpyruvate as co-substrate. Applying L-phenylalanine as a potential amino donor or using oxaloacetate or pyruvate as a replacement for 2-oxoglutarate as amino acceptor resulted in signifcantly lower catalytic efciencies in each of these cases. To facilitate further substrate search, two methods were introduced, one using ninhydrin after thin-layer chromatography and the other using derivatisation with o-phthalaldehyde followed by HPLC or LC–MS analysis. Both methods proved to be well applicable and helped to confrm the acceptance of further aromatic and aliphatic amino acids. This work presents the frst description of a heterologously expressed TAT from a hornwort (A. agrestis) and describes the possible entry into the biosynthesis of RA and other specialised compounds in a so far neglected representative of terrestrial plants and upcoming new model organism. [ABSTRACT FROM AUTHOR]

Catalytic cancer therapy targets cancer cells by exploiting the specific characteristics of the tumor microenvironment (TME). TME-based catalytic strategies rely on the use of molecules already present in the TME. Amino groups seem to be a suitable target, given the abundance of proteins and peptides in biological environments. Here we show that catalytic CuFe 2 O 4 nanoparticles are able to foster transaminations with different amino acids and pyruvate, another key molecule present in the TME. We observed a significant in cellulo decrease in glutamine and alanine levels up to 48 h after treatment. In addition, we found that di- and tripeptides also undergo catalytic transamination, thereby extending the range of the effects to other molecules such as glutathione disulfide (GSSG). Mechanistic calculations for GSSG transamination revealed the formation of an imine between the oxo group of pyruvate and the free -NH 2 group of GSSG. Our results highlight transamination as alternative to the existing toolbox of catalytic therapies.

Transaminase is a key enzyme for amino acid metabolism, which reversibly catalyzes the transamination reaction with the help of PLP (pyridoxal 5'-phosphate) as its cofactor. Here we have investigated the mechanism and free energy landscape of the transamination reaction involving the aspartate transaminase (AspTase) enzyme and aspartate-PLP (Asp-PLP) complex using QM/MM simulation and metadynamics methods. The reaction is found to follow a stepwise mechanism where the active site residue Lys258 acts as a base to shuttle a proton from a-carbon (CA) to imine carbon (C4A) of the PLP-Asp Schiff base. In the first step, the Lys258 abstracts the CA proton of the substrate leading to the formation of a carbanionic intermediate which is followed by the reprotonation of the Asp-PLP Schiff base at C4A atom by Lys258. It is found that the free energy barrier for the proton abstraction by Lys258 and that for the reprotonation are 17.85 and 3.57 kcal/mol, respectively. The carbanionic intermediate is 7.14 kcal/mol higher in energy than the reactant. Hence, the first step acts as the rate limiting step. The present calculations also show that the Lys258 residue undergoes a conformational change after the first step of transamination reaction and becomes proximal to C4A atom of the Asp-PLP Schiff base to favor the second step. The active site residues Tyr70* and Gly38 anchor the Lys258 in proper position and orientation during the first step of the reaction and stabilize the positive charge over Lys258 generated at the intermediate step. [ABSTRACT FROM AUTHOR]

Oxidative stress, an excess of reactive oxygen species (ROS), may lead to oxidative post-translational modifications of proteins resulting in the cleavage of the peptide backbone, known as α-amidation, and formation of fragments such as peptide amides and α-ketoacyl peptides (α-KaP). In this study, we first compared different approaches for the synthesis of different model α-KaP and then investigated their stability compared to the corresponding unmodified peptides. The stability of peptides was studied at room temperature or at temperatures relevant for food processing (100 °C for cooking and 150 °C as a simulation of roasting) in water, in 1% (m/v) acetic acid or as the dry substance (to simulate the thermal treatment of dehydration processes) by HPLC analysis. Oxidation of peptides by 2,5-di-tert-butyl-1,4-benzoquinone (DTBBQ) proved to be the most suited method for synthesis of α-KaPs. The acyl side chain of the carbonyl-terminal α-keto acid has a crucial impact on the stability of α-KaPs. This carbonyl group has a catalytic effect on the hydrolysis of the neighboring peptide bond, leading to the release of α-keto acids. Unmodified peptides were significantly more stable than the corresponding α-KaPs. The possibility of further degradation reactions was shown by the formation of Schiff bases from glyoxylic or pyruvic acids with glycine and proven through detection of transamination products and Strecker aldehydes of α-keto acids by HPLC–MS/MS. We propose here a mechanism for the decomposition of α-ketoacyl peptides. [ABSTRACT FROM AUTHOR]

Populus species are fast growing with high N requirements; an optimum level of fertilization is necessary for high seedling quality and subsequent plantation productivity. In this study, the morphological and physiological responses of two poplar clones (XH and BL3) to exponential and conventional N dosages were investigated, with a specific focus on leaf traits, the photorespiratory N cycle, and the interconversion of amino acids within leaves. Results show that shoot height and leaf number exponentially increased with plant growth. Leaf area, chlorophyll concentration, and net photosynthetic rate significantly increased for both clones during N fertilization, with a significant difference only in leaf area of clone XH between exponential and conventional dosages. Leaf concentrations of free amino acids and soluble sugars were not different but soluble proteins and fatty acids were significantly different for clone XH between N dosages; the amino acids glutamate, alanine, and aspartic acid concentrations increased in exponentially fertilized seedlings compared to controls. Amino acids, including the composition concentration and activity of glutamic-oxalacetic and -pyruvic transaminase, and soluble sugars were significantly higher for clone BL3 in fertilized seedlings. Photorespiration (glycine and glycolate oxidase) and glutathione redox (oxidized glutathione) were affected by fertilization. The activities of key enzymes (glycolate oxidase, catalase, and γ-glutamate cysteine ligase) involved in photorespiration and glutathione metabolism were lower for clone XH with exponential fertilization. Phenylalanine catabolism was influenced by fertilization and the interaction, clone × fertilization, showing accumulation of phenylalanine and tyrosine but decreases in phenylalanine ammonialyase activity and flavonoid concentrations in leaves of fertilized seedlings. The results indicate that leaf area and the interconversion of amino acids through deamidation/transamination are key regulatory hubs in poplar acclimation to soil N availability. • N application significantly improved poplar growth and physiological status. • The efficacy of N addition is determined by a combination of poplar clone and fertilization model. • Exponential N addition is a preferable fertilization strategy for clone XH. • Leaf area is significantly higher for clone XH under exponential than conventional N addition. • Photorespiratory N cycle, and leaf interconversion of amino acids are significant in poplar response to N fertilizations. • Phe catabolism through PAL to flavonoid is implicated in poplar acclimation to different N additions. [ABSTRACT FROM AUTHOR]

2-Amino-6-aryl-4-(dicyanomethylene)-3-azabicyclo[3.1.0]hex-2-ene-1,5-dicarbonitriles undergo transamination under the action of primary and secondary amines to form 2-(alkylamino)-6-aryl-4-(dicyanomethylene)-3-azabicyclo[3.1.0]hex-2-ene-1,5-dicarbonitriles. [ABSTRACT FROM AUTHOR]

• Validation of the transamination and decarboxylation. • Bioinformatics analysis and site-directed mutagenesis. • Changes in substrate preference of bifunctional enzymes. Aspartate aminotransferase (L-AspAT) is a highly substrate-specific biocatalyst for chiral amino acid splitting and unnatural amino acid synthesis, with both transamination and decarboxylation functions, but it is frequently interfered with each other in the catalytic process. The characterized mutant strains for the isolation of transamination and decarboxylation were obtained by bioinformatics analysis and site-directed mutagenesis in this research. The results showed that the mutants T296D and C180I enhanced decarboxylation by hydrogen bonding to α-ketoglutarate. In contrast, the mutants W130S and W130P increased the transamination activities to 157 % and 144 % of the WT respectively, which improved the binding efficiency through the expansion of the substrate binding pocket of the mutations. In addition, the catalytic efficiency of W130P for o-chlorobenzoylformate was also increased to 226 % of the WT, and the size of the binding pocket with o-chlorobenzoylformate was increased from 9.2 Å to 11.5 Å, a big change improved the probability of the substrate's entry. These results provided an extremely important idea and theoretical basis for changing the preference of bifunctional enzymes by mutating. [Display omitted] [ABSTRACT FROM AUTHOR]

The kinetic resolution of racemic amino acids mediated by dipeptides and pyridoxal provides a prebiotically plausible route to enantioenriched proteinogenic amino acids. The enzymatic transamination cycles that are key to modern biochemical formation of enantiopure amino acids may have evolved from this half of the reversible reaction couple. Kinetic resolution of racemic precursors emerges as a general route to enantioenrichment under prebiotic conditions., Competing Interests: Competing interests statement:The authors declare no competing interest.

New multipurpose arylation/acylation/transamination reagents, N‐acylisatins, have been developed by selective 'inside‐outside' C−N bond cleavage under different catalytic conditions. As activated amides, N‐acylisatins undergo Rh‐catalyzed C−H arylation and Pd‐catalyzed acylation by cleavage outside the C−N bond, and the desired biaryls and diaryl ketones were obtained in good to excellent yields. Generally, the combination of N‐acylisatins with amines leads to a ring‐opening reaction and formation of transamination products in a predictable manner through inside C−N bond cleavage. Interestingly, treatment of N‐acylisatins with amines lead to unexpected outer‐ring transamination products when CsF is added, which shows that CsF can favor the outside C−N bond cleavage path. Notably, this work presents a new strategy for multiple chemical transformations of a single amide to achieve various products by selective C−N bond cleavage. [ABSTRACT FROM AUTHOR]

Two biocatalytic reactions, transamination catalyzed by transaminases and reductive amination catalyzed by amino acid dehydrogenases, can be used for asymmetric synthesis of optically pure unnatural amino acids. However, although transaminases show a great diversity and broad substrate spectrum, most transaminase reactions are reversible, while amino acid dehydrogenases catalyze reductive amination irreversibly but with strict substrate specificity. Accordingly, herein we developed a tri‐enzyme one‐pot reaction system to exploit the respective advantages of transaminases and amino acid dehydrogenases, while overcoming the disadvantages of each. In this work, representatives of all four subgroups of transaminases coupled with different amino acid dehydrogenases to produce five l‐ and four d‐ unnatural amino acid products, using ammonia and the co‐enzyme NAD(P)H, which is regenerated by a robust alcohol dehydrogenase with 2‐propanol as cheap cosubstrate. The complete conversion and high enantiopurity (ee > 99 %) of the products, demonstrated it as an ideal alternative for asymmetric synthesis of chiral amino acid compounds. [ABSTRACT FROM AUTHOR]

Abstract Ti-based metal-organic frameworks (NH 2 -MIL-125) were post synthetic modified through a facile strategy using bis-quinoline Mannich bases producing MIL-125-HQ. The modified material (MIL-125-HQ) was used as an absorbent for uptake of the heavy metals from wastewater. 1H NMR, FTIR, CHN and SEM-EDX analysis showed successful incorporation of hydroxyl quinoline moiety into the NH 2 -MIL-125 upon chemical reaction. The modified MIL-125-HQ showed high affinity for Pb(II) ions from water, and the amount of Pb(II) ions decrease sharply from 500 mg/L to 60 mg/L, within merely 30 min of exposure at pH7, 298 K and 2 g/L MIL-125-HQ. The maximum adsorption capacity of MIL-125-HQ for Pb(II), Cd(II), Cu(II) and Cr(III) was determined to be 262.1, 102.8, 66.9 and 53.9 mg/g, respectively. Graphical abstract Image 1 Highlights • A porous Titanium-based metal-organic framework (MIL-125) was successfully modified with new Mannich bases via transamination reaction. • The modified MIL-125-HQ was applied to the water as filter to remove heavy metals and the results showed higher adsorption capacity compared with other absorbers. • The pseudo-second-order and Langmuir model can well describe the adsorption (R2 > 0.99). [ABSTRACT FROM AUTHOR]

Background: High-fiber diets (HFDs) are recommended in the diet of persons with diabetes, yet such diets can impair macronutrient digestion and/or absorption, modify insulin sensitivity, and reset metabolism.Objectives: We studied the effects of a HFD on the kinetics of whole-body protein, a macronutrient that could be affected by dietary fiber, in type 1 diabetes mellitus (T1DM), under both basal-low insulinemic and hyperinsulinemic conditions.Methods: Eight men with T1DM (body mass index range: 21.8-27.8 kg/m2) were studied twice - before and after the addition of guar gum (∼15 g/d) to their usual diet for ∼4 mo. Whole-body protein degradation (i.e., the rate of appearance [Ra] of endogenous leucine), leucine disposal to protein synthesis (PS), deamination, and reamination, were determined before and after the HFD, both in the postabsorptive state and following a euglycemic, hyperinsulinemic, hyperaminoacidemic clamp, using isotope dilution methods.Results: After the HFD, mean values (± SEs) for postabsorptive leucine Ra decreased by ∼20%: from 2.52 (0.15) to 2.03 (0.16) μmol x kg-1 x min-1, P < 0.049, after vs. before the HFD respectively. PS also decreased, by ∼25%: from 2.03 (0.15) to 1.57 (0.15), P < 0.045. Leucine concentration (P = 0.1) and reamination (P = 0.095) decreased moderately, whereas deamination was unchanged. Following the clamp, plasma amino acid concentrations (P < 0.001), leucine deamination (+ ∼50%, P < 0.00002), reamination (+ ∼30%, P < 0.0007), and PS (+ ∼35%, P < 0.00001) were all increased compared with postabsorptive state values, whereas endogenous leucine Ra was suppressed (by 15%, P < 0.00001, and by 25%, P < 0.001, with the primary or the reciprocal pool models, respectively). No significant differences in these insulin effects before compared with after the HFD were observed. Metabolic control (glycated hemoglobin), daily insulin requirement, and insulin-mediated glucose disposal were unchanged after the HFD.Conclusions: A HFD downregulates postabsorptive protein turnover in men with T1DM, by decreasing both protein degradation and synthesis, possibly due to a subtle decrease and/or delay in amino acid absorption. It does not significantly affect the insulin (and amino acid sensitivity) to protein turnover, glucose disposal, and metabolic control. [ABSTRACT FROM AUTHOR]

We describe a new labeling method that allows for full protonation at the backbone Hα position, maintaining protein side chains with a high level of deuteration. We refer to the method as alpha proton exchange by transamination (α-PET) since it relies on transaminase activity demonstrated here using Escherichia coli expression. We show that α-PET labeling is particularly useful in improving structural characterization of solid proteins by introduction of an additional proton reporter, while eliminating many strong dipolar couplings. The approach benefits from the high sensitivity associated with 1.3 mm samples, more abundant information including Hα resonances, and the narrow proton linewidths encountered for highly deuterated proteins. The labeling strategy solves amide proton exchange problems commonly encountered for membrane proteins when using perdeuteration and backexchange protocols, allowing access to alpha and all amide protons including those in exchange-protected regions. The incorporation of Hα protons provides new insights, as the close Hα–Hα and Hα–HN contacts present in β-sheets become accessible, improving the chance to determine the protein structure as compared with HN–HN contacts alone. Protonation of the Hα position higher than 90% is achieved for Ile, Leu, Phe, Tyr, Met, Val, Ala, Gln, Asn, Thr, Ser, Glu, Asp even though LAAO is only active at this degree for Ile, Leu, Phe, Tyr, Trp, Met. Additionally, the glycine methylene carbon is labeled preferentially with a single deuteron, allowing stereospecific assignment of glycine alpha protons. In solution, we show that the high deuteration level dramatically reduces R2 relaxation rates, which is beneficial for the study of large proteins and protein dynamics. We demonstrate the method using two model systems, as well as a 32 kDa membrane protein, hVDAC1, showing the applicability of the method to study membrane proteins. [ABSTRACT FROM AUTHOR]

The mechanism of transamination enzymes, urea, antioxidant protection in blood and liver of cattle afflicted with fascioliasis is studied. It was found that in the liver of infected animals, the most intensive formation of glutamic acid transamination occurs at aspartic acid and asparagine in α-ketoglutarate. Also, these animals have higher blood levels of urea, a higher activity of AST, ALT and catalase and the content of ceruloplasmin and peroxidase activity of SOD decreased.

[Display omitted] Reaction between 2-piperidinochromane and (hetero)aromatic amines in the presence of pyridinium tosylate affords the products of replacement of the piperidine fragment by the (hetero)arylamino moiety in good yields. This single-stage process opens facile and efficient way to the functionalized N -arylchroman-2-amines. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract A mild amino–enaminone 'click' polymerisation method for the preparation of polyenaminones by transamination of α,α′-bis-enaminocyclopentanones with diamines was developed. A series of 12 representative polymers were synthesised by acid-catalysed transamination of two bis-enaminones with six primary 1,2-, 1,3-, and 1,4-diamines. The method allows for combinatorial preparation of structurally diverse polyenaminones from easily available diamines and bis-enaminones. The reaction mechanism was studied by NMR and MS. It involves formation of open-chain and cyclic oligomers, which then undergo a step-wise polymerisation to furnish the title polymers with high average molecular weight (M w > 5.0 × 104 Da) and with spherical and porous microstructure. The obtained polymers were insoluble in most organic solvents, stable in diluted acids and bases, while degradable in concentrated hydrochloric acid at room temperature. They were thermally stable up to 200 °C and exhibited film-forming and UV–vis-shielding properties. [ABSTRACT FROM AUTHOR]

A series of 16 new ethyl β-amino benzimidazole acrylate derivatives 12(a-p) with a (2E)-s-cis/trans conformation and bearing two points of diversity was designed and synthesized by using a multi-step strategy (reductive amination, deprotection in acidic media and transamination) in moderate to good yields from ethyl 3-dimethylamino-2-(1H-benzimidazol-2-yl)acrylate (5) and monosubstituted N-Boc diamines (7a,7b) as starting building blocks. Products 12 were evaluated for their in vitro cytotoxic potential against six selected human cell lines (Huh7-D12, Caco2, MDA-MB231, HCT116, PC3 and NCI-H727). Compounds 12a, 12e and 12l exhibited selective and micromolar antitumor activities against Huh7-D12 and Caco2 cell lines. [ABSTRACT FROM AUTHOR]

Vinylogous urethane chemistry can provide the sustainable way to address the demands for reprocessing the cross-linked polymers. In this paper, we extended this method to prepare the existing commercially available cross-linked polybutadiene (PB) with multiple reprocessing ways. We firstly attach acetoacetyl group to the chains of PB and then use diamines as cross-linkers to form vinylogous urethanes involved network, which could be tailored with great freedom, including via the content of attached acetoacetyl group, the ratio of amine to acetoacetyl group and different types of amine. Furthermore, the dynamic nature of the cross-linked PB is studied by stress relaxation. Based on the Arrhenius equation, the activation energy for chain re-arrangement is calculated about 48 ± 5 kJ mol −1 and the network could be efficiently reshuffled at the temperature between 120 °C and 150 °C. More important, the cross-linked PB could be effectively remolded by hot pressing or solvent assisted welding methods via catalyst-free transamination of vinylogous urethanes. We envisage that this strategy may provide an eco-environmental method to dispose the waste rubbers and prolong their life time. [ABSTRACT FROM AUTHOR]

The first steps of leucine utilization are reversible deamination to α-ketoisocaproic acid (α-KIC) and irreversible oxidation. Recently, the regulatory role of leucine deamination over oxidation was underlined in rodents. Our aim was to measure leucine deamination and reamination in the whole body, in respect to previously determined rates across individual organs, in humans. By leucine and KIC isotope kinetics, we determined whole-body leucine deamination and reamination, and we compared these rates with those already reported across the sampled organs. As an in vivo counterpart of the 'metabolon' concept, we analysed ratios between oxidation and either deamination or reamination. Leucine deamination to KIC was greater than KIC reamination to leucine in the whole body ( p = 0.005), muscles ( p = 0.005), and the splanchnic area ( p = 0.025). These rates were not significantly different in the kidneys. Muscle accounted for ≈60% and ≈78%, the splanchnic bed for ≈15% and ≈15%, and the kidney for ≈12% and ≈18%, of whole-body leucine deamination and reamination rates, respectively. In the kidney, percent leucine oxidation over either deamination or reamination was >3-fold greater than muscle and the splanchnic bed. Skeletal muscle contributes by the largest fraction of leucine deamination, reamination, and oxidation. However, in relative terms, the kidney plays a key role in leucine oxidation. [ABSTRACT FROM AUTHOR]

Abstract: The reactions between N,N‐dimethyl enaminones and ortho‐aminothiophenols provide 1,4‐benzothiazines via cascade C−N bond transamination and C(sp2)−H sulfenylation. By employing biomass‐available ethyl lactate as a green medium, the present work offers a complementary metal‐free cross‐coupling‐based synthesis of 1,4‐benzothiazines to those known tandem reactions catalyzed by transition metals. [ABSTRACT FROM AUTHOR]