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Coordination compounds are molecules that contain one or more metal centers bound to ligands. Ligands can be atoms, ions, or molecules that transfer electrons to the metal. These compounds can be charged or neutral. When charged, neighboring counter-ions help stabilize the complex. The metal ion is located at the center of a complex ion, surrounded by other molecules or ions known as ligands. Ligands can be thought of as covalently bonded to the core ion through coordination. Understanding coordination theory in chemistry provides insight into the geometric shape of complexes and the structure of coordination compounds, which consist of a central atom or molecule connected to surrounding atoms or compounds. Inorganic coordination compounds exhibit different properties and are used in synthesizing organic molecules. The coordination of chemicals is vital for the survival of living organisms. Metal complexes are also essential for various biological processes, with many enzymes, known as metalloenzymes, being composed of metal complexes. These metal complexes occur naturally. [ABSTRACT FROM AUTHOR]

Eubacterium limosum is a dominant member of the human gut microbiome and produces short-chain fatty acids (SCFAs). These promote immune system function and inhibit inflammation, making this microbe important for human health. Lactate is a primary source of gut SCFAs but its utilization by E. limosum has not been explored. We show that E. limosum growing on lactate takes up added tungstate rather than molybdate and produces the SCFAs acetate and butyrate, but not propionate. The genes encoding an electron bifurcating, tungsten-containing oxidoreductase (WOR1) and a tungsten-containing formate dehydrogenase (FDH), along with an electron bifurcating lactate dehydrogenase (LCT), lactate permease, and enzymes of the propanediol pathway, are all up-regulated on lactate compared to growth on glucose. Lactate metabolism is controlled by a GntR-family repressor (LctR) and two global regulators, Rex and CcpA, where Rex in part controls W storage and tungstopyranopterin (Tuco) biosynthesis. Tuco-dependent riboswitches, along with CcpA, also control two iron transporters, consistent with the increased iron demand for many iron-containing enzymes, including WOR1 and FDH, involved in SCFA production. From intracellular aldehyde concentrations and the substrate specificity of WOR1, we propose that WOR1 is involved in detoxifying acetaldehyde produced during lactate degradation. Lactate to SCFA conversion by E. limosum is clearly highly tungstocentric and tungsten might be an overlooked micronutrient in the human microbiome and in overall human health. [ABSTRACT FROM AUTHOR]

Efficient and sustainable catalytic processes are crucial for advancing green chemical manufacturing. Here, we describe the synthesis of novel silver artificial metalloenzymes in colloidal form in aqueous media and room temperature. The strategy is based on the in situ generation of silver nanoparticles by a genetically modified Geobacillus thermocatenulatus lipase (GTL) in the active site as an inducer and scaffold protein, producing an enzyme–Ag bioconjugate. Using a structural analysis of the formation of silver nanoparticles by XRD and UV spectra, we found the formation of Ag2O species with nanoparticles of around 11 nm average diameter size. Gel filtration chromatography demonstrated the presence of single protein molecules in the bioconjugates, although silver nanoparticles were initially formed by cysteine coordination in the active site but later were formed in other parts of the protein (five AgNPs per molecules, which is in concordance with the UV size). The enzyme structure was altered after nanoparticle formation and Ag-S interaction, which was observed in fluorescence analysis. This new enzyme showed reductive activity against p-nitrophenol to p-amino and a high conversion > 99% in the reduction of acetophenone to phenylethanol, although the enantioselective was quite moderate but higher in water that in the presence of co-solvents. Finally, oxidase-like activity was evaluated in the direct oxidation of phenylethanol to acetophenone in water, obtained at around a 23% yield of ketone after 60 h. [ABSTRACT FROM AUTHOR]

Hydrogenases are a group of versatile metalloenzymes that catalyse the reversible transformation between hydrogen gas and its constituent protons and electrons. These enzymes have gained attention more recently due to their ability to use molecular hydrogen as a substrate in the reactions they catalyse, as well as their potential to synthesise hydrogen, an important biofuel. Although the existence of hydrogenases has been known since the 1930s, current research has not yet made them viable on the industrial scale. They are explored mostly from the biochemical point of view, which is very important, but there is a lack of research on how to adapt these enzymes for real industrial-scale processes. Only a few studies address this gap. Therefore, in this brief literature review, we provide an overview of what is known about hydrogenases. We explore their background, classification, and phylogeny, highlighting their presence in many different sources in nature, such as bacteria, archaea, and certain eukaryotes. We also discuss key factors influencing their activity, along with their advantages and disadvantages. Furthermore, we summarise the methods available for determining their activity and emphasise the need for standardised units to ensure comparability of all data available in the literature. Finally, we discuss their potential applications, particularly in hydrogen production and synthetic reaction pathways for coenzyme regeneration, emphasizing the critical importance of these aspects in the investigation of hydrogenases. [ABSTRACT FROM AUTHOR]

Various metalloenzymes employ O2 for oxidative reactions, which is crucial in catalysis and biological processes involving high-valent metal–oxygen species. This study introduces novel high-valent Co(III)–(μ-1,2-O2)–Co(IV) and Co(III)–(μ-1,2-O2˙−)–Co(III) complexes, stabilized by an electron-donating TPA* ligand. This study advances our understanding of Co–oxygen intermediates, which are key for water oxidation catalysis. [ABSTRACT FROM AUTHOR]

In this study, we aimed to develop protein‐based metal ligands to catalyze cis‐selective cyclopropanation using the TM1459 cupin protein superfamily. Copper complexes with TM1459 mutants containing the 3‐His metal‐binding site exhibited excellent diastereoselectivity in cyclopropanation reactions with styrene and ethyl diazoacetate. Further mutations in the secondary coordination sphere increased the cis‐preference with t‐butyl diazoacetate as the substrate with up to 80 : 20 (cis:trans ratio) and high enantioselectivity (90 % ee). [ABSTRACT FROM AUTHOR]

Transition metal catalysts (TMCs) mediated bioorthogonal catalysis expand the chemical possibilities within cells. Developing synthetic TMCs tools that emulate the efficiency and specificity of natural metalloenzymes is a rewarding yet challenging endeavor. Here, we highlight the potential of molecularly imprinted enzyme mimics (MIEs) containing a Cu center and specific substrate binding domain, for conducing dimethylpropargyloxycarbonyl (DmProc) cleavage reactions within cells. Our studies reveal that the Cu‐MIEs act as highly specific guides, precisely catalyzing target substrates, even in glutathione (GSH)‐rich cellular environments. By adapting templates similar to the target substrates, we evolved Cu‐MIEs activity to a high level and provided a method to broaden its scope to other unique substrates. This system was applied to a thyroid hormone (T3)‐responsive gene switch model, inducing firefly luciferase expression by T3 in cells. This approach verifies that MIEs effectively rescue DmProc‐bearing T3 prodrugs and seamlessly integrating themself into cellular biocatalytic networks. [ABSTRACT FROM AUTHOR]

The efficient production of microbial lipases from organic wastes has garnered great interest because of the diverse and potential biotechnological applications of these enzymes. However, the extracellular lipases from the novel yeast strains Hyphopichia wangnamkhiaoensis and Yarrowia deformans remain uncharacterized. Thus, this study aimed to investigate the characteristics and production of lipases from both yeasts. Lipases from H. wangnamkhiaoensis and Y. deformans were purified and biochemically characterized, and their production was measured in batch cultures with olive oil (reference), waste cooking oil, and glycerol as substrates. The purified lipases from H. wangnamkhiaoensis and Y. deformans had molecular weights of approximately 33 and 45 kDa, respectively. Their activities on p-nitrophenyl palmitate were optimal at pH 8.0 and 40 °C. Moreover, the activities of the lipases were inhibited by ethylenediaminetetraacetic acid, phenylmethylsulfonyl fluoride, and 4-(2-aminoethyl)benzenesulfonyl fluoride, and were reactivated by Ca2+ and Mg2+, indicating that both lipases are metalloenzymes and serine-type enzymes. The lipases were more tolerant to hydrophilic solvents than to hydrophobic solvents, and they followed Michaelis–Menten kinetics. Among the various substrates used, waste cooking oil yielded the highest lipase production and productivity. These results indicate that H. wangnamkhiaoensis and Y. deformans are suitable and potential candidates for lipase production. [ABSTRACT FROM AUTHOR]

It has been found that various heavy metals can initiate different types of regulated cell deaths. Among these metals, copper, an essential trace micronutrient that plays a major role in a lot of physiological processes, also can initiate cell death. It can act as a constituent of metalloenzymes, and can act as a mediator for signaling pathways to regulate proliferation and metastasis of tumor. It is also an integral part of some metal‐based anticancer drugs. Recent studies have revealed that excessive intracellular copper accumulation leads to the aggregation of mitochondrial lipoylated proteins, causing proteotoxic stress and ultimately resulting in cell death. This newly discovered copper‐induced cell death is termed as cuproptosis. In the last few years, a lot of research has been done to understand the mechanism of copper‐mediated cell death, and attempts have also been made to identify the relationship between cuproptosis and the development of cancer. In this review, we have provided a comprehensive overview on the significance of copper, its regulation inside the body, the possible mechanism of cuproptosis, and how this cuproptosis can be employed as a therapeutic tool for cancer ablation. [ABSTRACT FROM AUTHOR]

The micronutrient iron is essential for phytoplankton growth due to its central role in a wide variety of key metabolic processes including photosynthesis and nitrate assimilation. As a result of scarce bioavailable iron in seawater, marine primary productivity is often iron-limited with future iron supplies remaining uncertain. Although evolutionary constraints resulted in high cellular iron requirements, phytoplankton evolved diverse mechanisms that enable uptake of multiple forms of iron, storage of iron over short and long timescales, and modulation of their iron requirement under stress. Genomics continues to increase our understanding of iron-related proteins that are homologous to those characterized in other model organisms, while recently, molecular and cell biology have been revealing unique genes and processes with connections to iron acquisition or use. Moreover, there are an increasing number of examples showing the interplay between iron uptake and extracellular processes such as boundary layer chemistry and microbial interactions. [ABSTRACT FROM AUTHOR]

Biofilm‐associated infections pose complex challenges that require addressing the multifaceted requirements of biofilm disruption, bacterial killing, and immunomodulation. In this study, microenvironment‐adaptive metallo‐polymeric nanodecoys (MPNs) are synthesized through one‐pot subcomponent coordination in aqueous solution, effectively eradicating bacterial biofilms and modulating immune response. Within the acidic microenvironment of biofilms, the positively charged MPNs demonstrated the ability to interact with and eliminate bacteria while facilitating a Fenton‐like reaction for efficient eradication of bacterial biofilms. As the local microenvironment shifted from a neutral to a basic state during subsequent tissue healing processes, the MPNs adaptively harness the multiple properties to bind pathogen‐associated molecular patterns, scavenge reactive oxygen species, thereby modulating the immune response, alleviating inflammation, and promoting tissue healing. This study presents an efficient strategy for preparing enzyme‐mimicking materials that closely resemble natural metalloenzymes, and the MPNs offer an efficient alternative to current antibiotic treatments for biofilm‐associated infections. [ABSTRACT FROM AUTHOR]

Enzymes turnover substrates into products with amazing efficiency and selectivity and as such have great potential for use in biotechnology and pharmaceutical applications. However, details of their catalytic cycles and the origins surrounding the regio‐ and chemoselectivity of enzymatic reaction processes remain unknown, which makes the engineering of enzymes and their use in biotechnology challenging. Computational modelling can assist experimental work in the field and establish the factors that influence the reaction rates and the product distributions. A popular approach in modelling is the use of quantum mechanical cluster models of enzymes that take the first‐ and second coordination sphere of the enzyme active site into consideration. These QM cluster models are widely applied but often the results obtained are dependent on model choice and model selection. Herein, we show that QM cluster models can give highly accurate results that reproduce experimental product distributions and free energies of activation within several kcal mol−1, regarded that large cluster models with >300 atoms are used that include key hydrogen bonding interactions and charged residues. In this tutorial review, we give general guidelines on the set‐up and applications of the QM cluster method and discuss its accuracy and reproducibility. Finally, several representative QM cluster model examples on metal‐containing enzymes are presented, which highlight the strength of the approach. [ABSTRACT FROM AUTHOR]

Methods for producing drugs directly at the cancer site, particularly using bioorthogonal metal catalysts, are being explored to mitigate the side effects of therapy. Albumin‐based artificial metalloenzymes (ArMs) catalyze reactions in living mice while protecting the catalyst in the hydrophobic pocket. Here, we describe the in situ preparation and application of biocompatible tumor‐targeting ArMs using circulating albumin, which is abundant in the bloodstream. The ArM was formed using blood albumin through the intravenous injection of ruthenium conjugated with an albumin‐binding ligand; the tumor‐targeting unit was conjugated to the ArM using its catalytic activity, and the ArM was transported to the cancer site. The delivered ArM catalyzed a second tagging reaction of the proapoptotic peptide on the cancer surface, successfully suppressing cancer proliferation. This approach, which efficiently leveraged the persisting reactivity twice in vivo, holds promise for future in vivo metal‐catalyzed drug synthesis utilizing endogenous albumin. [ABSTRACT FROM AUTHOR]

The flexible acquisition of substrates from nutrient pools is critical for microbes to prevail in competitive environments. To acquire glucose from diverse glycoside and disaccharide substrates, many free‐living and symbiotic bacteria have developed, alongside hydrolysis, a non‐hydrolytic pathway comprised of four biochemical steps and conferred from a single glycoside utilization gene locus (GUL). Mechanistically, this pathway integrates within the framework of oxidation and reduction at the glucosyl/glucose C3, the eliminative cleavage of the glycosidic bond and the addition of water in two consecutive lyase‐catalyzed reactions. Here, based on study of enzymes from the phytopathogen Agrobacterium tumefaciens, we reveal a conserved Mn2+ metallocenter active site in both lyases and identify the structural requirements for specific catalysis to elimination of 3‐keto‐glucosides and water addition to the resulting 2‐hydroxy‐3‐keto‐glycal product, yielding 3‐keto‐glucose. Extending our search of GUL‐encoded putative lyases to the human gut commensal Bacteroides thetaiotaomicron, we discover a Ca2+ metallocenter active site in a putative glycoside hydrolase‐like protein and demonstrate its catalytic function in the eliminative cleavage of 3‐keto‐glucosides of opposite (α) anomeric configuration as preferred by the A. tumefaciens enzyme (β). Structural and biochemical comparisons reveal the molecular‐mechanistic origin of 3‐keto‐glucoside lyase stereo‐complementarity. Our findings identify a basic set of GUL‐encoded lyases for glucoside metabolism and assign physiological significance to GUL genetic diversity in the bacterial domain of life. [ABSTRACT FROM AUTHOR]

[NiFe] hydrogenases catalyze the reversible cleavage of molecular hydrogen into protons and electrons. Here, we have studied the impact of temperature and illumination on an oxygen‐tolerant and thermostable [NiFe] hydrogenase by IR and EPR spectroscopy. Equilibrium mixtures of two catalytic [NiFe] states, Nia‐C and Nia‐SR", were found to drastically change with temperature, indicating a thermal exchange of electrons between the [NiFe] active site and iron‐sulfur clusters of the enzyme. In addition, IR and EPR experiments performed under illumination revealed an unusual photochemical response of the enzyme. Nia‐SR", a fully reduced hydride intermediate of the catalytic cycle, was found to be reversibly photoconverted into another catalytic state, Nia‐L. In contrast to the well‐known photolysis of the more oxidized hydride intermediate Nia‐C, photoconversion of Nia‐SR" into Nia‐L is an active‐site redox reaction that involves light‐driven electron transfer towards the enzyme's iron‐sulfur clusters. Omitting the ground‐state intermediate Nia‐C, this direct interconversion of these two states represents a potential photochemical shortcut of the catalytic cycle that integrates multiple redox sites of the enzyme. In total, our findings reveal the non‐local redistribution of electrons via thermal and photochemical reaction channels and the potential of accelerating or controlling [NiFe] hydrogenases by light. [ABSTRACT FROM AUTHOR]

The sublethal toxic effects of pyriproxyfen, an insect juvenile hormone analog (JHA) insecticide, on the circulating metabolite balance in the Neotropical brown stink bug, Euschistus heros, one of the main agronomic pests in South America, were investigated. Our objectives were to evaluate changes in the baseline levels of lipids and carbohydrates, along with three selected micro-elements—nickel (Ni), copper (Cu), and zinc (Zn)—in the hemolymph of adult E. heros, following the application of a predetermined LC30 of pyriproxyfen (single topical application) in fourth-instar nymphs (N4). Hemolymph was sampled using glass capillaries, with the resulting concentrations of lipids and carbohydrates determined through vanillin- and anthrone-positive reactions, respectively, and micro-element analysis was performed through total reflection X-ray fluorescence (TXRF) spectrometry. Lipids are the main and more stable energy metabolites for E. heros, with a proportion of 2:1 compared to carbohydrate levels. A remarkable sensitivity of carbohydrate levels to sublethal pyriproxyfen exposure, irrespective of sex, was observed. Baseline micro-element levels based on untreated control insects indicate sex-based differences in Ni and Zn, but not in Cu, concentrations. After insecticide exposure, the levels of these micro-elements were variable, with Ni and Zn generally decreasing and Cu decreasing in females but nearly doubling in males. The observed disproportion in lipids, carbohydrates, and inorganic micro-elements suggests potential physiological shifts triggered by pyriproxyfen activity in E. heros during late juvenile stages. [ABSTRACT FROM AUTHOR]

Human carbonic anhydrase II (hCAII) naturally catalyzes the reaction between two achiral molecules—water and carbon dioxide—to yield the achiral product carbonic acid through a zinc hydroxide intermediate. We have previously shown that a zinc hydride, instead of a hydroxide, can be generated in this enzyme to create a catalyst for the reduction of aryl ketones. Dialkyl ketones are more challenging to reduce, and the enantioselective reduction of dialkyl ketones with two alkyl groups that are similar in size and electronic properties, is a particularly challenging transformation to achieve with high activity and selectivity. Here, we show that hCAII, as well as a double mutant of it, catalyzes the enantioselective reduction of dialkyl ketones with high yields and enantioselectivities, even when the two alkyl groups are similar in size. We also show that variants of hCAII catalyze the site‐selective reduction of one ketone over the other in an unsymmetrical aliphatic diketone. Computational docking of a dialkyl ketone to variants of hCAII containing the zinc hydride provides insights into the origins of the reactivity of various substrates and the high enantioselectivity of the transformations and show how a confined environment can control the enantioselectivity of an abiological intermediate. [ABSTRACT FROM AUTHOR]

Design of metal cofactor ligands is essential for controlling the reactivity of metalloenzymes. We investigated a carbene transfer reaction catalyzed by myoglobins containing iron porphyrin cofactors with one and two trifluoromethyl groups at peripheral sites (FePorCF3 and FePor(CF3)2, respectively), native heme and iron porphycene (FePc). These four myoglobins show a wide range of Fe(II)/Fe(III) redox potentials in the protein of +147 mV, +87 mV, +42 mV and −198 mV vs. NHE, respectively. Myoglobin reconstituted with FePor(CF3)2 has a more positive potential, which enhances the reactivity of a carbene intermediate with alkenes, and demonstrates superior cyclopropanation of inert alkenes, such as aliphatic and internal alkenes. In contrast, engineered myoglobin reconstituted with FePc has a more negative redox potential, which accelerates the formation of the intermediate, but has low reactivity for inert alkenes. Mechanistic studies indicate that myoglobin with FePor(CF3)2 generates an undetectable active intermediate with a radical character. In contrast, this reaction catalyzed by myoglobin with FePc includes a detectable iron–carbene species with electrophilic character. This finding highlights the importance of redox‐focused design of the iron porphyrinoid cofactor in hemoproteins to tune the reactivity of the carbene transfer reaction. [ABSTRACT FROM AUTHOR]

Zinc (Zn) is a vital trace element that plays a pivotal role in protein synthesis, cellular growth, and differentiation and is involved as a cofactor of metalloenzymes, performing a wide variety of metabolic, immune, and synthesis roles. Zn is required at all stages of an infant's and child's development, and severe Zn deficiency has been reported to lead to slower physical, cognitive, and sexual growth. Preterm neonates are at a higher risk of developing zinc deficiency for a variety of reasons, including low Zn intake from enteral feeds containing breast milk, relative malabsorption due to immaturity of the gastrointestinal tract with limited absorptive capacity, increased urinary loss of zinc, and increased demand during the early developmental stages. Moreover, premature infants are at risk of gastrointestinal diseases like necrotizing enterocolitis (NEC), which can limit absorption capacity and potentially lead to malabsorption. TPN is frequently used in preterm infants to provide them with sufficient nutrients and calories. However, it has its own complications, including cholestasis, especially if used for prolonged periods. In this case report, we are presenting the case of a male preterm infant who was delivered by caesarean section at 26 weeks' gestation. The baby developed an intestinal perforation due to NEC, for which he underwent surgery for resection of the necrotic bowel and the creation of a high ileal stoma and was put on prolonged total parenteral nutrition (TPN), which led to the development of zinc deficiency. [ABSTRACT FROM AUTHOR]

Enzyme engineering is a powerful tool for improving or altering the properties of biocatalysts for industrial, research, and therapeutic applications. Fast and accurate screening of variant libraries is often the bottleneck of enzyme engineering and may be overcome by growth-based screening strategies with simple processes to enable high throughput. The currently available growth-based screening strategies have been widely employed for enzymes but not yet for catalytically potent and oxygen-sensitive metalloenzymes. Here, we present a screening system that couples the activity of an oxygen-sensitive formate dehydrogenase to the growth of Escherichia coli. This system relies on the complementation of the E. coli formate hydrogenlyase (FHL) complex by Mo-dependent formate dehydrogenase H (EcFDH-H). Using an EcFDH-Hdeficient strain, we demonstrate that growth inhibition by acidic glucose fermentation products can be alleviated by FHL complementation. This allows the identification of catalytically active EcFDH-H variants at a readily measurable cell density readout, reduced handling efforts, and a low risk of oxygen contamination. Furthermore, a good correlation between cell density and formate oxidation activity was established using EcFDH-H variants with variable catalytic activities. As proof of concept, the growth assay was employed to screen a library of 1,032 EcFDH-H variants and reduced the library size to 96 clones. During the subsequent colorimetric screening of these clones, the variant A12G exhibiting an 82.4% enhanced formate oxidation rate was identified. Since many metal-dependent formate dehydrogenases and hydrogenases form functional complexes resembling E. coli FHL, the demonstrated growth-based screening strategy may be adapted to components of such electron-transferring complexes. [ABSTRACT FROM AUTHOR]

The global proliferation of carbapenemase-producing bacteria (CPB) has garnered significant attention worldwide. Early diagnosis of CPB and accurate identification of carbapenemases are crucial for preventing the spread of CPB and ensuring targeted antibiotic therapy. Therefore, efficient and accurate identification of carbapenemases is paramount in clinically treating diseases associated with CPB. In this study, 58 CPB strains were collected and detected using the DNA endonuclease-targeted CRISPR trans reporter (DETECTR) method, a rapid detection platform based on CRISPR-Cas12a gene editing and isothermal amplification. Additionally, four conventional methods (the APB/EDTA method, PCR, NG-test Carba 5, and GeneXpert Carba-R) were employed and compared against whole genome sequencing (WGS) results, considered the gold standard, to evaluate their efficacy in detecting carbapenemases. Detection by the APB/EDTA method revealed that 29 strains were positive for Class A serine endopeptidases, while 29 strains were positive for Class B metalloenzymes. The classification of these zymotypes was consistent with the sequencing result. All target carbapenemases for KPC were identified with 100% sensitivity using NG-test Carba 5, PCR, DETECTR, and GeneXpert Carba-R. In the case of NDM, both Xpert Carba-R and DETECTR showed a sensitivity of 100%. In contrast, NG-test Carba 5 and PCR had a slightly lower sensitivity of 96.7%, each missing one target carbapenemase. n this study, the APB/EDTA method is capable of identifying the zymotype classification but not the specific resistant genes, while Xpert Carba-R and DETECTR are able to detect all target carbapenemases. [ABSTRACT FROM AUTHOR]

One of the seven natural CO2 fixation pathways, the anaerobic Wood-Ljungdahl pathway (WLP) is unique in generating CO as a metabolic intermediate, operating through organometallic intermediates, and in conserving (versus utilizing) net ATP. The key enzyme in the WLP is acetyl-CoA synthase (ACS), which uses an active site [2Ni-4Fe-4S] cluster (A-cluster), a CO tunnel, and an organometallic (Ni-CO, Ni-methyl, and Ni-acetyl) reaction sequence to generate acetyl-CoA. Here, we reveal that an alcove, which interfaces the tunnel and the A-cluster, is essential for CO2 fixation and autotrophic growth by the WLP. In vitro spectroscopy, kinetics, binding, and in vivo growth experiments reveal that a Phe229A substitution at one wall of the alcove decreases CO affinity thirty-fold and abolishes autotrophic growth; however, a F229W substitution enhances CO binding 80-fold. Our results indicate that the structure of the alcove is exquisitely tuned to concentrate CO near the A-cluster; protect ACS from CO loss during catalysis, provide a haven for inhibitory CO, and stabilize the tetrahedral coordination at the Nip site where CO binds. The directing, concentrating, and protective effects of the alcove explain the inability of F209A to grow autotrophically. The alcove also could help explain current controversies over whether ACS binds CO and methyl through a random or ordered mechanism. Our work redefines what we historically refer to as the metallocenter "active site". The alcove is so crucial for enzymatic function that we propose it is part of the active site. The community should now look for such alcoves in all "gas handling" metalloenzymes. [ABSTRACT FROM AUTHOR]

An Artificial Metalloenzyme (ArM) built employing the streptavidin‐biotin technology has been used for the enantioselective synthesis of binaphthyls by means of asymmetric Suzuki‐Miyaura cross‐coupling reactions. Despite its success, it remains a challenge to understand how the length of the biotin cofactors or the introduction of mutations to streptavidin leads the preferential synthesis of one atropisomer over the other. In this study, we apply an integrated computational modeling approach, including DFT calculations, protein‐ligand dockings and molecular dynamics to rationalize the impact of mutations and length of the biotion cofactor on the enantioselectivities of the biaryl product. The results unravel that the enantiomeric differences found experimentally can be rationalized by the disposition of the first intermediate, coming from the oxidative addition step, and the entrance of the second substrate. The work also showcases the difficulties facing to control the enantioselection when engineering ArM to catalyze enantioselective Suzuki‐Miyaura couplings and how the combination of DFT calculations, molecular dockings and MD simulations can be used to rationalize artificial metalloenzymes. [ABSTRACT FROM AUTHOR]

Astonishing progress has been achieved in unlocking new‐to‐nature biocatalysis in the past decades. The progress in protein engineering enabled research to efficiently incorporate artificial structural elements into enzyme design. Recent trends include cofactor mimetics, artificial metalloenzymes and non‐canonical amino acids. In this perspective article, we present the state‐of‐the‐art, discuss recent examples and our view on what we call artificial biocatalysis. Although these artificial systems undoubtedly increase the scope of biocatalysis, their applicability remains challenging. Fundamental questions regarding the impact of this research field are addressed in this perspective. [ABSTRACT FROM AUTHOR]

The recently discovered Type 9 Secretion System (T9SS) is present in bacteria of the Fibrobacteres–Bacteroidetes–Chlorobi superphylum, which are key constituents of diverse microbiomes. T9SS is instrumental in the extracellular secretion of over 270,000 proteins, including peptidases, sugar hydrolases, metal ion‐binding proteins, and metalloenzymes. These proteins are essential for the interaction of bacteria with their environment. This mini‐review explores the extensive array of proteins secreted by the T9SS. It highlights the diverse functions of these proteins, emphasizing their roles in pathogenesis, bacterial interactions, host colonization, and the overall health of the ecosystems inhabited by T9SS‐containing bacteria. [ABSTRACT FROM AUTHOR]

The excessive production of various reactive oxidant species over endogenous antioxidant defense mechanisms leads to the development of a state of oxidative stress, with serious biological consequences. The consequences of oxidative stress depend on the balance between the generation of reactive oxidant species and the antioxidant defense and include oxidative damage of biomolecules, disruption of signal transduction, mutation, and cell apoptosis. Accumulating evidence suggests that oxidative stress is involved in the physiopathology of various debilitating illnesses associated with chronic inflammation, including cardiovascular diseases, diabetes, cancer, or neurodegenerative processes, that need continuous pharmacological treatment. Oxidative stress and chronic inflammation are tightly linked pathophysiological processes, one of which can be simply promoted by another. Although, many antioxidant trials have been unsuccessful (some of the trials showed either no effect or even harmful effects) in human patients as a preventive or curative measure, targeting oxidative stress remains an interesting therapeutic approach for the development of new agents to design novel anti-inflammatory drugs with a reliable safety profile. In this regard, several natural antioxidant compounds were explored as potential therapeutic options for the treatment of chronic inflammatory diseases. Several metalloenzymes, such as superoxide dismutase, catalase, and glutathione peroxidase, are among the essential enzymes that maintain the low nanomolar physiological concentrations of superoxide (O2⋅-) and hydrogen peroxide (H2O2), the major redox signaling molecules, and thus play important roles in the alteration of the redox homeostasis. These enzymes have become a striking source of motivation to design catalytic drugs to enhance the action of these enzymes under pathological conditions related to chronic inflammation. This review is focused on several major representatives of natural and synthetic antioxidants as potential drug candidates for the treatment of chronic inflammatory diseases. [ABSTRACT FROM AUTHOR]

The immobilisation of artificial metalloenzymes (ArMs) holds promise for the implementation of new biocatalytic reactions. We present the synthesis of cross-linked artificial metalloenzyme aggregates (CLArMAs) with excellent recyclability, as an alternative to carrier-based immobilisation strategies. Furthermore, iron-siderophore supramolecular anchoring facilitates redox-triggered cofactor release, enabling CLArMAs to be recharged with alternative cofactors for diverse selectivity. [ABSTRACT FROM AUTHOR]

Lytic polysaccharide monooxygenases (LPMOs) are Cu‐dependent metalloenzymes that catalyze the hydroxylation of strong C−H bonds in polysaccharides using O2 or H2O2 as oxidants (monooxygenase/peroxygenase). In the absence of C−H substrate, LPMOs reduce O2 to H2O2 (oxidase) and H2O2 to H2O (peroxidase) using proton/electron donors. This rich oxidative reactivity is promoted by a mononuclear Cu center in which some of the amino acid residues surrounding the metal might accept and donate protons and/or electrons during O2 and H2O2 reduction. Herein, we utilize a podal ligand containing H‐bond/proton donors (LH2) to analyze the reactivity of mononuclear Cu species towards O2 and H2O2. [(LH2)CuI]1+ (1), [(LH2)CuII]2+ (2), [(LH−)CuII]1+ (3), [(LH2)CuII(OH)]1+ (4), and [(LH2)CuII(OOH)]1+ (5) were synthesized and characterized by structural and spectroscopic means. Complex 1 reacts with O2 to produce 5, which releases H2O2 to generate 3, suggesting that O2 is used by LPMOs to generate H2O2. The reaction of 1 with H2O2 produces 4 and hydroxyl radical, which reacts with C−H substrates in a Fenton‐like fashion. Complex 3, which can generate 1 via a reversible protonation/reduction, binds H2O and H2O2 to produce 4 and 5, respectively, a mechanism that could be used by LPMOs to control oxidative reactivity. [ABSTRACT FROM AUTHOR]

Spin state switching in the metal center is a crucial phenomenon in many enzymatic reactions in biology. The spin state alteration, a critical step in cytochrome P450 catalysis, is driven most likely through a weak perturbation upon substrate binding in the enzyme, which is still not well clarified. In the current work, the spin state transition of iron(III) from high to intermediate via an admixed state is observed upon a subtle electronic perturbation to the sulphonate moieties coordinated axially to a diiron(III)porphyrin dimer. While electron‐donating substituents stabilize the high‐spin state of iron(III), strongly electron‐withdrawing groups stabilize an intermediate‐spin state, whereas the moderate electron‐withdrawing nature of axial ligands resulted in an admixed state. Confirmation of the molecular structures and their spin states have been made utilizing single‐crystal X‐ray structure analysis, Mössbauer, magnetic, EPR, and 1H NMR spectroscopic investigations. The position of the signals of the porphyrin macrocycle in the paramagnetic 1H NMR is found to be very characteristic of the spin state of the iron center in solution. The Curie plot for the pure high‐spin complexes shows the signals′ temperature dependency in line with the Curie law. Conversely, the pure intermediate‐spin state of iron exhibits an anti‐Curie temperature dependence, whereas the admixed‐spin state of iron displays significant curvature of the lines in the Curie plot. An extensive DFT analysis displays a linear dependence between the energy difference between dx2-y2 ${{_{x{^{2}}- y{^{2}}}}}$ and dz2 ${{_{z{^{2}}}}}$ orbital versus Fe−Npor distance for the complexes reported here. Furthermore, a strong linear correlation between the Fe−O distance and the spin density over the oxygen atom, as well as the Fe−Npor distance for the complexes, has been observed. Thus, a slight electronic perturbation at the axial ligand of the diheme resulted in a large change in the electronic structures with a spin‐flip. This is at par with the metalloenzymes, which employ minute perturbations around the periphery of the active sites, leading to spin state transitions. [ABSTRACT FROM AUTHOR]

In addition to its primary oxygen-atom-transfer function, cysteamine dioxygenase (ADO) exhibits a relatively understudied anaerobic disproportionation reaction (ADO-Fe(III)-SR → ADO-Fe(II) + ½ RSSR) with its native substrates. Inspired by ADO disproportionation reactivity, we employ [Fe(tacn)Cl3] (tacn = 1,4,7-triazacyclononane) as a precursor for generating Fe(III)–thiolate model complexes in buffered aqueous media. A series of Fe(III)–thiolate model complexes are generated in situ using aqueous [Fe(tacn)Cl3] and thiol-containing ligands cysteamine, penicillamine, mercaptopropionate, cysteine, cysteine methyl ester, N-acetylcysteine, and N-acetylcysteine methyl ester. We observe trends in UV–Vis and electron paramagnetic resonance (EPR) spectra, disproportionation rate constants, and cathodic peak potentials as a function of thiol ligand. These trends will be useful in rationalizing substrate-dependent Fe(III)–thiolate disproportionation reactions in metalloenzymes. [ABSTRACT FROM AUTHOR]

The sublethal toxic effects of pyriproxyfen, an insect juvenile hormone analog (JHA) insecticide, on the circulating metabolite balance in the Neotropical brown stink bug, Euschistus heros, one of the main agronomic pests in South America, were investigated. Our objectives were to evaluate changes in the baseline levels of lipids and carbohydrates, along with three selected micro-elements—nickel (Ni), copper (Cu), and zinc (Zn)—in the hemolymph of adult E. heros, following the application of a predetermined LC30 of pyriproxyfen (single topical application) in fourth-instar nymphs (N4). Hemolymph was sampled using glass capillaries, with the resulting concentrations of lipids and carbohydrates determined through vanillin- and anthrone-positive reactions, respectively, and micro-element analysis was performed through total reflection X-ray fluorescence (TXRF) spectrometry. Lipids are the main and more stable energy metabolites for E. heros, with a proportion of 2:1 compared to carbohydrate levels. A remarkable sensitivity of carbohydrate levels to sublethal pyriproxyfen exposure, irrespective of sex, was observed. Baseline micro-element levels based on untreated control insects indicate sex-based differences in Ni and Zn, but not in Cu, concentrations. After insecticide exposure, the levels of these micro-elements were variable, with Ni and Zn generally decreasing and Cu decreasing in females but nearly doubling in males. The observed disproportion in lipids, carbohydrates, and inorganic micro-elements suggests potential physiological shifts triggered by pyriproxyfen activity in E. heros during late juvenile stages.

Background: N-acetylmuramyl-L-alanine amidases are cell wall modifying enzymes that cleave the amide bond between the sugar residues and stem peptide in peptidoglycan. Amidases play a vital role in septal cell wall cleavage and help separate daughter cells during cell division. Most amidases are zinc metalloenzymes, and E. coli cells lacking amidases grow as chains with daughter cells attached to each other. In this study, we have characterized two amidase enzymes from Deinococcus indicus DR1. D. indicus DR1 is known for its high arsenic tolerance and unique cell envelope. However, details of their cell wall biogenesis remain largely unexplored. Results: We have characterized two amidases Ami1Di and Ami2Di from D. indicus DR1. Both Ami1Di and Ami2Di suppress cell separation defects in E. coli amidase mutants, suggesting that these enzymes are able to cleave septal cell wall. Ami1Di and Ami2Di proteins possess the Amidase_3 catalytic domain with conserved –GHGG- motif and Zn2+ binding sites. Zn2+- binding in Ami1Di is crucial for amidase activity. AlphaFold2 structures of both Ami1Di and Ami2Di were predicted, and Ami1Di was a closer homolog to AmiA of E. coli. Conclusion: Our results indicate that Ami1Di and Ami2Di enzymes can cleave peptidoglycan, and structural prediction studies revealed insights into the activity and regulation of these enzymes in D. indicus DR1. [ABSTRACT FROM AUTHOR]

Metalloenzymes catalyze a wide range of chemical transformations, with the active site residues playing a key role in modulating chemical reactivity and selectivity. Unlike smaller synthetic catalysts, a metalloenzyme active site is embedded in a larger protein, which makes interrogation of electronic properties and geometric features with quantum mechanical calculations challenging. Here we implement the ability to fetch crystallographic structures from the Protein Data Bank and analyze the metal binding sites in the program molSimplify. We show the usefulness of the newly created protein3D class to extract the local environment around non‐heme iron enzymes containing a two histidine motif and prepare 372 structures for quantum mechanical calculations. Our implementation of protein3D serves to expand the range of systems molSimplify can be used to analyze and will enable high‐throughput study of metal‐containing active sites in proteins. [ABSTRACT FROM AUTHOR]

Metalloenzymes are ubiquitously present in the human body and are relevant to a variety of diseases. However, the development of metalloenzyme inhibitors is limited by low specificity and poor drug-likeness associated with metal-binding fragments (MBFs). A generalized drug discovery strategy was established, which is characterized by the property characterization of zinc-dependent metalloenzyme inhibitors (ZnMIs). Fifteen potential Zn2+-binding fragments (ZnBFs) were identified, and a customized pharmacophore feature was defined based on these ZnBFs. The customized feature was set as a required feature and applied to a search for novel inhibitors for histone deacetylase 1 (HDAC1). Ten potential HDAC1 inhibitors were recognized, and one of them (compound 9) was a known potent HDAC1 inhibitor. The results demonstrated the effectiveness of our strategy to identify novel inhibitors for zinc-dependent metalloenzymes. [ABSTRACT FROM AUTHOR]

Rieske dioxygenases are multi-component enzyme systems, naturally found in many soil bacteria, that have been widely applied in the production of fine chemicals, owing to the unique and valuable oxidative dearomatization reactions they catalyze. The range of practical applications for these enzymes in this context has historically been limited, however, due to their limited substrate scope and strict selectivity. To overcome these limitations, our research group has employed the tools of enzyme engineering to expand the substrate scope or improve the reactivity of these enzyme systems in specific contexts. Traditionally, enzyme engineering campaigns targeting metalloenzymes have avoided mutations to metal-coordinating residues, based on the assumption that these residues are essential for enzyme activity. Inspired by the success of other recent enzyme engineering reports, our research group investigated the potential to alter or improve the reactivity of Rieske dioxygenases by altering or eliminating iron coordination in the active site of these enzymes. Herein, we report the modification of all three iron-coordinating residues in the active site of toluene dioxygenase both to alternate residues capable of coordinating iron, and to a residue that would eliminate iron coordination. The enzyme variants produced in this way were tested for their activity in the czs-dihydroxylation of a small library of potential aromatic substrates. The results of these studies demonstrated that all three iron-coordinating residues, in their natural state, are essential for enzyme activity in toluene dioxygenase, as the introduction of any mutations at these sites resulted in a complete loss of czs-dihydroxylation activity for all substrates tested. [ABSTRACT FROM AUTHOR]

Developing enzyme alternatives is pivotal to improving and enabling new processes in biotechnology and industry. Artificial metalloenzymes (ArMs) are combinations of protein scaffolds with metal elements, such as metal nanoclusters or metal‐containing molecules with specific catalytic properties, which can be customized. Here, we engineered an ArM based on the consensus tetratricopeptide repeat (CTPR) scaffold by introducing a unique histidine residue to coordinate the hemin cofactor. Our results show that this engineered system exhibits robust peroxidase‐like catalytic activity driven by the hemin. The expression of the scaffold and subsequent coordination of hemin was achieved by recombinant expression in bulk and through in vitro transcription and translation systems in water‐in‐oil drops. The ability to synthesize this system in emulsio paves the way to improve its properties by means of droplet microfluidic screenings, facilitating the exploration of the protein combinatorial space to discover improved or novel catalytic activities. [ABSTRACT FROM AUTHOR]

Quercetin is the most abundant polyphenolic flavonoid (flavonol subclass) in vegetal foods and medicinal plants. This dietary chemopreventive agent has drawn significant interest for its multiple beneficial health effects ("polypharmacology") largely associated with the well-documented antioxidant properties. However, controversies exist in the literature due to its dual anti-/pro-oxidant character, poor stability/bioavailability but multifaceted bioactivities, leaving much confusion as to its exact roles in vivo. Increasing evidence indicates that a prior oxidation of quercetin to generate an array of chemical diverse products with redox-active/electrophilic moieties is emerging as a new linkage to its versatile actions. The present review aims to provide a comprehensive overview of the oxidative conversion of quercetin by systematically analyzing the current quercetin-related knowledge, with a particular focus on the complete spectrum of metabolite products, the enzymes involved in the catabolism and the underlying molecular mechanisms. Herein we review and compare the oxidation pathways, protein structures and catalytic patterns of the related metalloenzymes (phenol oxidases, heme enzymes and specially quercetinases), aiming for a deeper mechanistic understanding of the unusual biotransformation behaviors of quercetin and its seemingly controversial biological functions. [ABSTRACT FROM AUTHOR]

The inhibitory action of Schiff base complexes of 3d metals against the urease enzyme is well explored in the scientific community. However, the ability of such complexes in mimicking active metallobiosites of urease enzymes, possessing ureolytic behavior, still remains unexplored. With this aim firstly, two Zn(II)-complexes (PPR-HMB-Zn and PZ-HMB-Zn) have been developed from two different Schiff base ligands (HL1 = 2-((E)-(2-(piperidin-1-yl)ethylimino)methyl)-5-methylphenol and HL2 = 2-((E)-(2-(piperizin-1-yl)ethylimino)methyl)-5-methylphenol) and structurally characterized using single crystal XRD. The hydrolytic enzymatic activity of both complexes was demonstrated by the gradual increase in the absorption maxima at 425 nm for the formation of the p-nitrophenolate ion from catalytic hydrolysis mediated by the Zn(II) complexes with a disodium salt of p-nitrophenyl phosphate as a model substrate. Associated kinetic parameters, pH dependency and a relevant hydrolysis mechanism have also been explored. After confirming the hydrolytic ability, the complexes were exploited to mimic the hydrolytic activity of Jack bean urease that catalytically hydrolyses urea into ammonia and CO2. The change in the pH of the solution owing to the formation of ammonia under the complex catalysed hydrolytic action of urea has been monitored spectrophotometrically using the pH dependent structural change of phenol red. The amount of ammonia has been quantified using the Nessler's reagent spectrophotometric method. The ureolytic reaction mechanism has been investigated using density functional theory (DFT) calculations using the B3LYP and TPSSH methods for the systematic calculation of the interaction energy. In contrast to PZ-HMB-Zn, PPR-HMB-Zn functions more effectively as a catalyst due to the existence of a lattice-occluded water molecule in its crystal structure and the protonation of the non-terminal N to attract urea by H-bonding, which was further confirmed by AIM analysis. [ABSTRACT FROM AUTHOR]

Metalloenzymes are able to catalyze complex biochemical reactions in cellular (aqueous) media with high efficiency. In recent years, a variety of metal-containing single-chain nanoparticles (SCNPs) have been synthesized as simplified metalloenzyme-mimetic nano-objects. However, most of the metal-containing SCNPs reported so far contained complexed metal ions but not metal nanoclusters (NCs) with diameter <5 nm, which could be used as powerful, emerging catalysts. Herein, we report the synthesis of gold nanoclusters (Au-NCs) within SCNPs and the further use of Au-NCs/SCNPs as catalytic nanoreactors in water. We demonstrate that a common motif contained in several drugs (i.e., the aminophenyl–oxazolidinone fragment present in Rivaroxaban, Sutezolid, and Linezolid) can be efficiently prepared in water from a hydrophobic precursor compound by using the Au-NCs/SCNPs as efficient catalytic nanoreactors. In summary, this work paves the way forthe synthesis of metal–NCs/SCNPs for advanced catalysis in aqueous media. [ABSTRACT FROM AUTHOR]

Encapsulating drugs in poly(lactic‐co‐glycolic acid) (PLGA) nanoparticles can provide a gradual and consistent drug release. Herein, diclofenac sodium‐encapsulated PLGA nanoparticles (DS‐PLGA NPs) were synthesized, characterized, and their effects on bacterial proteolysis and elastolytic activity were evaluated using skim milk agar plate, elastin‐congo red, and staphylolysin disk susceptibility assays. Quantitative PCR was employed to examine the effect of nanoparticles on the expression of lasA/B genes. The DS‐PLGA NPs displayed spherical morphology with an average size of 86 nm, zeta potential of ‐15.2 mV, and DLS size of 124.6 nm. At a sub‐inhibitory concentration, DS‐PLGA NPs inhibited bacterial elastolytic activity by 41.6 to 62.1% during 30–180 min of incubation. The elastolytic curve slopes of samples from PLGA and DS‐PLGA treated groups were respectively 0.0714 and 0.0380 activity/min, indicating a significant reduction of bacterial extracellular elastases by DS‐PLGA NPs. Exposure of bacteria to a sub‐inhibitory concentration of the nanoparticles attenuated the expression of the lasA and lasB genes by 0.21 and 0.31 folds, respectively. Attenuation of the proteolytic activity of P. aeruginosa suggests that the antivirulence potential of the DS‐PLGA NPs along with the anti‐inflammatory properties of diclofenac sodium, can be considered for the treatment of acute and chronic P. aeruginosa infections. [ABSTRACT FROM AUTHOR]

Natural metalloenzymes with astonishing reaction activity and specificity underpin essential life transformations. Nevertheless, enzymes only operate under mild conditions to keep sophisticated structures active, limiting their potential applications. Artificial metalloenzymes that recapitulate the catalytic activity of enzymes can not only circumvent the enzymatic fragility but also bring versatile functions into practice. Among them, metal–organic frameworks (MOFs) featuring diverse and site-isolated metal sites and supramolecular structures have emerged as promising candidates for metalloenzymes to move toward unparalleled properties and behaviour of enzymes. In this review, we systematically summarize the significant advances in MOF-based metalloenzyme mimics with a special emphasis on active pocket engineering at the atomic level, including primary catalytic sites and secondary coordination spheres. Then, the deep understanding of catalytic mechanisms and their advanced applications are discussed. Finally, a perspective on this emerging frontier research is provided to advance bioinspired catalysis. [ABSTRACT FROM AUTHOR]

Benthodytes occidentpalauta sp. nov. was collected from the Kyushu-Palau Ridge at a depth of 5 481 m in 2021. This new species is characterized by a gelatinous body wall, violet skin, six pairs of dorsal papillae, and a rough mid-ventral surface without tube feet. The dorsal deposits are rod-shaped and tripartite. Two types of papillae deposits as crosses with four arms with central bipartite apophyses. Ventral deposits are rods. Tentacle ossicles are rod-shaped with end protrusions. Gonad deposits are rod-shaped, tripartite, and cross-shaped. The phylogenetic analyses based on cytochrome oxidase subunit 1 (COI) and 16S individually and a concatenated dataset of COI and 16S genes of this species support that B. occidentpalauta sp. nov. belongs to Benthodytes. [ABSTRACT FROM AUTHOR]

Methyl parathion hydrolase (MPH) is an enzyme of the metallo‐β‐lactamase superfamily, which hydrolyses a wide range of organophosphates (OPs). Recently, MPH has attracted attention as a promising enzymatic bioremediator. The crystal structure of MPH enzyme shows a dimeric form, with each subunit containing a binuclear metal ion center. MPH also demonstrates metal ion‐dependent selectivity patterns. The origins of these patterns remain unclear but are linked to open questions about the more general role of metal ions in functional evolution and divergence within enzyme superfamilies. We aimed to investigate and compare the binding of different OP pesticides to MPH with cobalt(II) metal ions. In this study, MPH was modeled from Ochrobactrum sp. with different OP pesticides bound, including methyl paraoxon and dichlorvos and profenofos. The docked structures for each substrate optimized by DFT calculation were selected and subjected to atomistic molecular dynamics simulations for 500 ns. It was found that alpha metal ions did not coordinate with all the pesticides. Rather, the pesticides coordinated with less buried beta metal ions. It was also observed that the coordination of beta metal ions was perturbed to accommodate the pesticides. The binding free energy calculations and structure‐based pharmacophore model revealed that all the three substrates could bind well at the active site. However, profenofos exhibit a stronger binding affinity to MPH in comparison to the other two substrates. Therefore, our findings provide molecular insight on the binding of different OP pesticides which could help us design the enzyme for OP pesticides degradation. [ABSTRACT FROM AUTHOR]

Significant improvements of the density functional theory (DFT) methodology during the past few decades have made DFT calculations a powerful tool in studies of enzymatic reaction mechanisms. For metalloenzymes, however, there are still concerns about the reliability in the DFT-results. Therefore, a systematic study is performed where the fraction of exact exchange in a hybrid DFT functional is used as a parameter. By varying this parameter, a set of different but related functionals are obtained. The various functionals are applied to one of the reactions occurring in the enzyme family heme–copper oxidases, the reduction of nitric oxide (NO) to nitrous oxide (N2O) and water. The results show that, even though certain parts of the calculated energetics exhibit large variations, the qualitative pictures of the reaction mechanisms are quite stable. Furthermore, it is found that the functional with 15% exact exchange (B3LYP*) gives the best agreement with experimental data for the particular reactions studied. An important aspect of the procedure used is that the computational results are carefully combined with a few more general experimental data to obtain a complete description of the entire catalytic cycle of the reactions studied. [ABSTRACT FROM AUTHOR]