Oxidative Deamination Reaction Research Articles

EXPLORATION OF PYRAZOLINE AND AMINO CHALCONE DERIVATIVES AS MONOAMINE OXIDASE INHIBITORS: AN IN-SILICO APPROACH

Monoamine oxidase (MAO) is an enzyme involved in neurotransmitter monoamine metabolism through an oxidative deamination reaction that produces a nerve-damaging substance, H2O2. Two isoforms of MAO that are MAO-A, and MAO-B, are known by their specific substrates, serotonin, and dopamine, respectively. Overexpression of MAO-A causes depression and anxiety disorder, whereas MAO-B causes neurodegenerative disorders such as Parkinson’s and Alzheimer’s. Infections and diseases caused by the activity of these two enzymes are known to affect millions of people worldwide every year. Various drugs for both disorders are available on the market. However, side effects such as dizziness, sore throat, insomnia, obesity, and heart disorder are registered. Therefore, developing new compounds acting as MAO inhibitors with lower side effects but higher selectivity than available drugs is in need. Pyrazolines and amino chalcone derivatives are well known to exhibit inhibition of MAO activity and used as research objects. Virtual screening of molecular docking using DOCK6 of six compounds of each pyrazoline (1a-f) (both R and S configuration) and amino chalcone (2a-f) was conducted to study their inhibition activity to MAO-A (PDB: 2Z5X) and MAO-B (PDB: 6FW0) and selectivity based on comparison of grid score value of Harmin as control positive for MAO-A and E92 ligand for MAO-B. The results showed that the most potent compound as a selective inhibitor of MAO is (R)-3-(4-aminophenyl)-5-phenyl-4,5-dihydro-1H-pyrazole-1-carboxamide of pyrazoline derivative and (1- (4-cinnamoyl phenyl) thiourea) of amino chalcone derivative.

Pt Nanoparticles with Enhanced Deaminase‐like Activity: Example of Oxidative Deamination of 5‐Hydroxymethylfurfurylamine and Glutamic Acid

AbstractOxidative deamination is part of the metabolic pathways of amino acid oxidase and glutamate dehydrogenase enzymes, and enables obtaining α‐keto acid from amino compound with ammonia as a by‐product. This work presents the utilization of Pt‐based catalyst composed of small platinum nanoparticles supported on industrial silica support (Pt/SiO2). This nanozyme was tested in the oxidative deamination reaction of two amino compounds: 5‐hydroxymethylfurfurylamine (HMFA) to 5‐hydroxymethylfurfural (HMF) and glutamic acid (GA) to α‐ketoglutaric acid (KGA). This paper outlines the use of Pt nanozymes with deaminase‐like activity. We showed the ability of this nanozymes to be selective and active in liquid phase oxidative deamination of HMFA and glutamic acid in a 6 to 9 pH range at 60 °C under atmospheric pressure. Pt/SiO2 nanozyme actually plays as a deaminase mimic with high HMFA conversion (60%) and cumulative yield to the corresponding desaminated keto compounds (67%).

Inhibition of histamine accumulation by novel histamine-degrading species of Staphylococcus sp. isolated from goats and sheep milk.

Histamine is an active amine compound that occurs in various fermented foods that may cause adverse effects on the human health. Certain microorganisms are able to degrade histamine by an oxidative deamination reaction. Therefore, the present study aimed to quantify histamine‐forming and/or ‐degrading activity of the isolates derived from milk of goat and sheep herds, in Iran, by the capillary zone electrophoresis (CZE) method; and we evaluated the molecular characteristics of staphylococcal isolates. Among 243 staphylococcal isolates, 29 histamine‐degrading bacteria were identified. One of these isolates, identified as Staph. epidermidis, No. 605, exhibited the highest activity compared to others, degrading available histamine to 58.33% within 24 h. By polymerase chain reaction (PCR) analysis, the isolate, No. 605 that exhibited remarkable histamine‐degrading activity lacked the genes encoding coagulase and DNase, nor did it harbor any of the five classical enterotoxin genes. This is the first report to show that seven Staphylococcus species, including Staph. chromogenes, Staph. aureus, Staph. haemolyticus, Staph. epidermidis, Staph. pseudintermedius, Staph. agnetis, and Staph. hyicus, were able to degrade histamine, which were hitherto not known to have this capacity. Therefore, histamine‐degrading activity is a definite criterion to introduce fermenting organisms able to decrease histamine content in different food products.

Cu/Ag mediated peroxide-free synthesis of benzoylated naphthol derivatives

A peroxide-free methodology was developed for the synthesis of benzoylated naphthol/phenol derivatives through oxidative deamination reaction performed under aerobic reaction conditions. A synergistic combination of Cu(OTf)2 and Ag2O was used to convert the aminonaphthols and aminophenols to the corresponding benzoylated derivatives. The definite role of atmospheric oxygen to assist the reaction was proved by performing the reaction in the argon atmosphere.

Characterization of Alanine Dehydrogenase and Its Effect on Streptomyces coelicolorA3(2) Development in Liquid Culture

Streptomyces, the most important group of industrial microorganisms, is harvested in liquid cultures for the production of two-thirds of all clinically relevant secondary metabolites. It is demonstrated here that the growth of Streptomyces coelicolor A3(2) is impacted by the deletion of the alanine dehydrogenase (ALD), an essential enzyme that plays a central role in the carbon and nitrogen metabolism. A long lag-phase growth followed by a slow exponential growth of S. coelicolor due to ALD gene deletion was observed in liquid yeast extract mineral salt culture. The slow lag-phase growth was replaced by the normal wild-type like growth by ALD complementation engineering. The ALD enzyme from S. coelicolor was also heterologously cloned and expressed in Escherichia coli for characterization. The optimum enzyme activity for the oxidative deamination reaction was found at 30°C, pH 9.5 with a catalytic efficiency, k_cat/K_M, of 2.0 ± 0.1 mM^–1 s^–1. The optimum enzyme activity for the reductive amination reaction was found at 30°C, pH 9.0 with a catalytic efficiency, k_cat/K_M, of 1.9 ± 0.1 mM^–1 s^–1.

Inhibition of Semicarbazide-sensitive Amine Oxidase Reduces Atherosclerosis in Cholesterol-fed New Zealand White Rabbits

Inflammation, oxidative stress, and the formation of advanced glycated end-products (AGEs) are important components of atherosclerosis. Vascular adhesion protein-1 (VAP-1) participates in inflammation. Its enzymatic activity, semicarbazide-sensitive amine oxidase (SSAO), can catalyze oxidative deamination reactions to produce hydrogen peroxide and aldehydes, leading to the subsequent generation of AGEs. This study aimed to investigate the effect of VAP-1/SSAO inhibition on atherosclerosis. In our study, immunohistochemical staining showed that atherosclerotic plaques displayed higher VAP-1 expression than normal arterial walls in apolipoprotein E-deficient mice, cholesterol-fed New Zealand White rabbits and humans. In cholesterol-fed rabbits, VAP-1 was expressed on endothelial cells and smooth muscle cells in the thickened intima of the aorta. Treatment with PXS-4728A, a selective VAP-1/SSAO inhibitor, in cholesterol-fed rabbits significantly decreased SSAO-specific hydrogen peroxide generation in the aorta and reduced atherosclerotic plaques. VAP-1/SSAO inhibition also lowered blood low-density lipoprotein cholesterol, reduced the expression of adhesion molecules and inflammatory cytokines, suppressed recruitment and activation of macrophages, and decreased migration and proliferation of SMC. In conclusion, VAP-1/SSAO inhibition reduces atherosclerosis and may act through suppression of several important mechanisms for atherosclerosis.

Biomimetic Oxidative Deamination Catalysis via ortho-Naphthoquinone-Catalyzed Aerobic Oxidation Strategy

An ortho-naphthoquinone-catalyzed oxidative deamination reaction has been developed where the molecular oxygen and water serve as the sole oxidant and nucleophile. The current aerobic deamination reaction proceeds via the ketimine formation between ortho-naphthoquinones and amines followed by the prototropic rearrangement and hydrolysis by water, representing a biomimetic oxidative deamination of amine species in the human body by the liver and kidneys. The compatibility of ortho-naphthoquinone organocatalysts with molecular oxygen and water opens up a new biomimetic catalyst system that can function as versatile deaminases for a variety of amine-containing molecules such as amino acids and DNA nuclear bases.

Dynamic hydrogels produced via monoamine oxidase B-catalyzed deamination and aldimine crosslinking for 3D printing.

Dynamic hydrogels were prepared via an oxidative deamination reaction catalyzed by monoamine oxidase B. Amino-containing polysaccharides (or proteins) and oxidative products (aldehydes) formed the dynamic Schiff base linkages, which endowed the hydrogel with excellent self-healing and multiresponsive properties.

Oxidative Deamination of N-Acetyl Neuraminic Acid: Substituent Effects and Mechanism.

A study of the mechanism of the oxidative deamination of the N-nitroso-N-acetyl sialyl glycosides leading with overall retention of configuration to the corresponding 2-keto-3-deoxy-D-glycero-D-galacto-nonulopyranosidonic acid (KDN) glycosides is described, making use of a series of differentially O-protected N-nitroso-N-acetyl sialyl glycosides and of isotopic labeling studies. No evidence is found for stereodirecting participation by ester groups at the 4- and 7-positions. Comparisons are drawn with oxidative deamination reactions of 4-amino-4-deoxy and 2-amino-2-deoxy hexopyranosides and a common mechanism is formulated involving the intermediacy of 1-oxabicyclo[3.1.0]hexyl oxonium ions following participation by the pyranoside ring oxygen. A minor reaction pathway has been uncovered by labeling studies in the β-thiosialosides that results in the exchange of the 4-O-acetyl group by the glacial acetic acid that serves as external nucleophile in the general oxidative deamination process. A mechanism is proposed for this exchange involving participation by the thioglycoside at the level of an intermediate diazoalkane.

Evaluation of the active site of phenylalanine dehydrogenase isolated from Bacillus badius using homology based modeling

Introduction: The enzyme, Phenylalanine dehydrogenase (L-phe DH; NAD oxidoreductase, deaminating; EC 1.4.1.20) belongs to the amino acid dehydrogenase family of enzymes which catalyzes the reversible oxidative deamination reaction of L-phenylalanine to their respective α- ketoacids. An assay technique with a high sensitivity for blood L-phenylalanine level, an important marker for the screening of Phenylketonuria (PKU), has been established by means of PheDH. This enzyme is being used as a commercial and valuable biocatalyst in medical and pharmaceutical industries. The enzymes of this family are closely related in structure and function. Methods: Swiss-Pdb Viewer used for analysis and Rhodococcus sp. M4 was chosen because of the availability of several crystal structures with bound substrates and its high specific activity. Results : Rhodococcus sp. M4 and B. badius PheDHs are very different from each other on a sequence level, sharing only 32% identity and 50% similarity. Coming from the same structural sub-family, they share a much stronger correlation in their folding motifs. Conclusions: Since there currently is no crystal structure available for the B. badius PheDH, the sequence was folded over the 1BW9 crystal structure and superimposed over the original scaffold using SuperPose.

H2O2-oxidation of α-aminoisobutyric and cyclic amino acids catalyzed by iron(III) isoindoline complexes

Series of dichloroiron(III) complexes of 1,3-bis(2′-arylimino)isoindoline have been used as catalysts for the oxidative decarboxylation and deamination reaction of acyclic [α-aminoisobutyric acid (AIBH)] and cyclic amino acids [1-aminocyclohexane-1-carboxylic acid (ACHH), 1-aminocyclopentane-1-carboxylic acid (ACPH), 1-aminocyclobutane-1-carboxylic acid (ACBH), 1-aminocyclopropane-1-carboxylic acid (ACCH)] to ethylene or the corresponding carbonyl compounds. We have found that the title complexes are very efficient and selective as catalysts, and linear correlations were observed between the reaction rate and the oxidation potential, E°′pa of the iron complexes, and the endocyclic bond angle of the substrates used.

Computer modelling of monoaminoxidases

The article summarized results of studies on active site structures of monoamine oxidases (MAO) performed in the Institute of Biomedical Chemistry (Russia) by computer modelling approaches. MAO, catalyzing the reaction of oxidative deamination of major neurotransmitter monoamines, exists in two highly homologous forms, MAO A and MAO B, distinguished by substrate specificity and inhibitor selectivity. The development of approaches for active site modelling of these enzymes (with unknown three-dimensional structures) started from analysis of relationship between the geometrical sizes of rigid indole and isatin derivatives and their inhibitory activity. These studies resulted in molding of the active site structures of MAO A and MAO B. These molds reflect the sizes and shapes of active sites of these enzymes. These mold models have been used for virtual screening of molecular databases for new inhibitors. The models obtained at different stages of MAO investigations have been compared with recently appeared three-dimensional structures of MAO A and MAO B.

Molecular cloning, characterization and function analysis of a GDH gene from Sclerotinia sclerotiorum in rice

The full-length cDNA encoding a glutamate dehydrogenase (GDH) which catalyzes the reaction of reductive amination of α-oxoglutarate (α-OG) to glutamate (the anabolic activity) and the reverse reaction of oxidative deamination of glutamate (the catabolic activity) was isolated from Sclerotinia sclerotiorum, we designated it as SsGDH. Bioinformatics analysis revealed that SsGDH had a typical GDH spatial structure and extensive homology with other fungal or bacteria GDHs. To evaluate its function in rice, rice (Oryza sativa L. cv. 'kitaake') was transformed with SsGDH in a binary vector construct by Agrobacterium-mediated transformation. Transgenic rice plants showed that transcripts and proteins of SsGDH accumulated at higher levels and GDH enzymatic activity was obviously higher in transgenic rice plants compared with the non-transformant rice plants (CK), though phenotype including plant height, fresh weight and dry weight became slightly weaker compared with CK under 50, 500 and 5,000 μM nitrogen gradient nutrient solution treatment (NH4NO3 as a nitrogen source) after introducing SsGDH into rice. For enzymatic activity assay in vitro, recombinant His6-SsGDH protein was expressed in Escherichia coli BL21 (DE3) and purified by Ni-NTA agarose. Results suggested that recombinant His6-SsGDH protein had GDH activity using ammonium, α-OG, and L-glutamate separately as a substrate at two different concentrations, especially the affinity for ammonium was very high, and its Km value was only 0.28 ± 0.03 mM, indicating that SsGDH can assimilate more ammonium into rice. According to previous reports, transgenic plants expressing fungal or bacteria GDHs might show improved herbicide resistance. Basta resistance test showed that SsGDH expression in rice can significantly enhanced their tolerance to Basta than CK. In conclusion, our results may provide some clues for further investigation on nitrogen utilization via introducing exogenous GDHs from lower organisms into rice.

Aerobic Degradation of N-Methyl-4-Nitroaniline (MNA) by Pseudomonas sp. Strain FK357 Isolated from Soil

N-Methyl-4-nitroaniline (MNA) is used as an additive to lower the melting temperature of energetic materials in the synthesis of insensitive explosives. Although the biotransformation of MNA under anaerobic condition has been reported, its aerobic microbial degradation has not been documented yet. A soil microcosms study showed the efficient aerobic degradation of MNA by the inhabitant soil microorganisms. An aerobic bacterium, Pseudomonas sp. strain FK357, able to utilize MNA as the sole carbon, nitrogen, and energy source, was isolated from soil microcosms. HPLC and GC-MS analysis of the samples obtained from growth and resting cell studies showed the formation of 4-nitroaniline (4-NA), 4-aminophenol (4-AP), and 1, 2, 4-benzenetriol (BT) as major metabolic intermediates in the MNA degradation pathway. Enzymatic assay carried out on cell-free lysates of MNA grown cells confirmed N-demethylation reaction is the first step of MNA degradation with the formation of 4-NA and formaldehyde products. Flavin-dependent transformation of 4-NA to 4-AP in cell extracts demonstrated that the second step of MNA degradation is a monooxygenation. Furthermore, conversion of 4-AP to BT by MNA grown cells indicates the involvement of oxidative deamination (release of NH2 substituent) reaction in third step of MNA degradation. Subsequent degradation of BT occurs by the action of benzenetriol 1, 2-dioxygenase as reported for the degradation of 4-nitrophenol. This is the first report on aerobic degradation of MNA by a single bacterium along with elucidation of metabolic pathway.

D-Amino Acid Oxidase Inhibitors as a Novel Class of Drugs for Schizophrenia Therapy

Over the years, accumulating evidence has indicated that D-serine represents the endogenous ligand for the glycine modulatory binding site on the NR1 subunit of N-methyl-D-aspartate receptors in various brain areas. Cellular concentrations of D-serine are regulated by synthesis due to the enzyme serine racemase (isomerization reaction) and by degradation due to the same enzyme(elimination reaction) as well as by the FAD-containing flavoenzyme D-amino acid oxidase (DAAO, oxidative deamination reaction).Several findings have linked low levels of D-serine to schizophrenia: D-serine concentrations in serum and cerebrospinal fluid have been reported to be decreased in schizophrenia patients while human DAAO activity and expression are increased; oral administration of D-serine improved positive, negative, and cognitive symptoms of schizophrenia as add-on therapy to typical and atypical antipsychotics.This evidence indicates that increasing NMDA receptor function, perhaps by inhibiting DAAO-induced degradation of D-serine may alleviate symptoms in schizophrenic patients. Furthermore, it has been suggested that co-administration of D-serine with a human DAAO inhibitor may be a more effective means of increasing D-serine levels in the brain. Here, we present an overview of the current knowledge of the structure-function relationships in human DAAO and of the compounds recently developed to inhibit its activity (specifically the ones recently exploited for schizophrenia treatment).

Investigating the oxidation of alkenes by non-heme iron enzyme mimics

Iron is emerging as a key player in the search for efficient and environmentally benign methods for the functionalisation of C-H bonds. Non-heme iron enzymes catalyse a diverse array of oxidative chemistry in nature, and small-molecule complexes designed to mimic the non-heme iron active site have great potential as C-H activation catalysts. Herein we report the synthesis of a series of organic ligands that incorporate key features of the non-heme iron active site. Iron(II) complexes of these ligands have been generated in situ and their ability to promote hydrocarbon oxidation has been investigated. Several of these systems promote the biomimetic dihydroxylation of cyclohexene at low levels, when hydrogen peroxide is used as the oxidant; allylic oxidation products are also observed. An investigation of ligand stability reveals formation of several breakdown products under the conditions of the oxidative turnover reactions. These products arise via oxidative decarboxylation, dehydration and deamination reactions. Taken together these results indicate that competing mechanisms are at play with these systems: biomimetic hydroxylation involving high-valent iron species, and allylic oxidation via Fenton chemistry and Haber-Weiss radical pathways.

Glutamate dehydrogenase of the germinating triticale seeds: gene expression, activity distribution and kinetic characteristics

On the cross-roads of main carbon and nitrogen metabolic pathways, glutamate dehydrogenase (GDH, E.C. 1.4.1.2) carries out the reaction of reductive amination of 2-oxoglutarate to glutamate (the anabolic activity; NAD(P)H–GDH), and the reverse reaction of oxidative deamination of glutamic acid (the catabolic activity; NAD(P)+–GDH). To date, there have been no reports on identification of GDH genes in cereals. Here, we report cloning and biochemical characterization of the GDH from germinating triticale seeds, a common Polish cereal. A single TsGDH1 gene is 1,620 bp long, while its 1,236 bp long open reading frame encodes a protein of 411 amino acids of high homology with the published GDH protein sequences from other plants. Phylogenetic analyses locate the TsGDH1 among other monocotyledonous proteins and among the sequences of the β-type subunit of plant GDHs. Changes in TsGDH1 expression and the dynamics of enzyme activity in germinating seeds confirm the existence of one TsGDH isoform with varying expression and activity patterns, depending on the tissue localization and stage of germination. The four-step purification method (including the anionite chromatography using HPLC) resulted in a protein preparation with a high-specific activity and purification factor of approx. 230. The purified enzyme exhibited an absolute specificity towards 2-oxoglutarate (NAD(P)H–GDH), or towards l-glutamate in the reverse reaction (NAD(P)+–GDH), while its low Km constants towards all substrates and co-enzymes may suggest its aminating activity during germination, or, alternatively, its capability to adjust the direction of the catalyzed reaction according to the metabolic necessity.

Interaction between glutamate dehydrogenase (GDH) and l-leucine catabolic enzymes: Intersecting metabolic pathways

Branched-chain amino acids (BCAAs) catabolism follows sequential reactions and their metabolites intersect with other metabolic pathways. The initial enzymes in BCAA metabolism, the mitochondrial branched-chain aminotransferase (BCATm), which deaminates the BCAAs to branched-chain α-keto acids (BCKAs); and the branched-chain α-keto acid dehydrogenase enzyme complex (BCKDC), which oxidatively decarboxylates the BCKAs, are organized in a supramolecular complex termed metabolon. Glutamate dehydrogenase (GDH1) is found in the metabolon in rat tissues. Bovine GDH1 binds to the pyridoxamine 5′-phosphate (PMP)-form of human BCATm (PMP-BCATm) but not to pyridoxal 5′-phosphate (PLP)-BCATm in vitro. This protein interaction facilitates reamination of the α-ketoglutarate (αKG) product of the GDH1 oxidative deamination reaction. Human GDH1 appears to act like bovine GDH1 but human GDH2 does not show the same enhancement of BCKDC enzyme activities. Another metabolic enzyme is also found in the metabolon is pyruvate carboxylase (PC). Kinetic results suggest that PC binds to the E1 decarboxylase of BCKDC but does not effect BCAA catabolism. The protein interaction of BCATm and GDH1 promotes regeneration of PLP-BCATm which then binds to BCKDC resulting in channeling of the BCKA products from BCATm first half reaction to E1 and promoting BCAA oxidation and net nitrogen transfer from BCAAs. The cycling of nitrogen through glutamate via the actions of BCATm and GDH1 releases free ammonia. Formation of ammonia may be important for astrocyte glutamine synthesis in the central nervous system. In peripheral tissue association of BCATm and GDH1 would promote BCAA oxidation at physiologically relevant BCAA concentrations.

The kinetic properties of the glutamate dehydrogenase of Teladorsagia circumcincta and their significance for the lifestyle of the parasite

Like other nematodes, both L(3) and adult Teladosagia circumcincta secrete or excrete NH(3)/NH(4)(+), but the reactions involved in the production are unclear. Glutamate dehydrogenase is a significant source NH(3)/NH(4)(+) in some species, but previous reports indicate that the enzyme is absent from L(3)Haemonchus contortus. We show that glutamate dehydrogenase was active in both L(3) and adult T. circumcincta. The apparent K(m)s of the L(3) enzyme differed from those of the adult enzyme, the most significant of these being the increase in the K(m) for NH(4)(+) from 18mM in L(3) to 49mM in adults. The apparent V(max) of the oxidative deamination reaction was greater than that of the reductive reaction in L(3), but this was reversed in adults. The activity of the oxidative reaction of the L(3) enzyme was not affected by adenine nucleotides, but that of the reductive reaction was stimulated significantly by either ADP or ATP. The L(3) enzyme was more active with NAD(+) than it was with NADP(+), although the activities supported by NADH and NADPH were similar at saturating concentrations. While the activity of the oxidative reaction was sufficient to account for the NH(3)/NH(4)(+) efflux we have previously reported, the reductive amination reaction was likely to be more active.

Oxygen influence on amino acid oxidative deamination catalyzed by different amino acid oxidases

Amino acid oxidases catalyze oxidative deamination of a wide range of amino acids to their corresponding  -keto acids. In this work two D-amino acid oxidases: from porcine kidney and Arthrobacter protophormiae were compared in their action in the reaction of D-methionine oxidative deamination. Special attention has been paid to the oxygen influence on enzyme activity. Kinetics of the reaction was determined by the initial reaction rate method by the standard peroxidase-o-dianisidine enzyme assay. The oxygen impact on the initial reaction rate was measured by following the oxygen consumption during the reaction at different initial oxygen concentration. Kinetic parameters were estimated from the experimental results by using the non-linear regression analysis implemented in the package program SCIENTIST. It was found that both enzymes have similar affinities towards D-methionine as well as oxygen ( (porcine kidney)=0.13 mM, (A. protophormiae)=0.22 mM). Both enzymes are inhibited by 2-oxo-4-methylthiobutyric acid, and the inhibition constant is lower in the case of porcine kidney enzyme which indicates higher inhibition. Oxygen volume transfer coefficient (kLa) has been determined at different air flow-rates using integral. Mathematical model of the process that consists of kinetic and mass balance equations has been developed in the batch reactor. The experiments without and with continuous oxygen (air) supply were carried out to validate the mathematical model. The reaction solution was initially saturated with air to achieve the maximum oxygen solubility at the experimental conditions. Considering that oxygen is one of the reactants spent in the reaction, the reaction rate in the initial part of the experiments is faster if air is supplied to the reactor. In the case of porcine kidney oxidase the reaction was very slow without the air supply. 100 % D-methionine conversion was achieved after 12 hours. Another two experiments were carried out at the continuous air supply (flow-rates 5 and 10 L/h). The reaction went faster in the initial part of both experiments ; however enzyme deactivation occurred and prevented the complete substrate conversion. In the case of oxidase from A. protophormiae experiments without and with the air supply (flow-rate 10 L/h) were carried. In both cases 100 % D-methionine conversion could be achieved. This enzyme was more tolerant to oxygen since enzyme deactivation constant (kd = 7.9  10-5 min-1) was found to be several orders of magnitude lower than the ones estimated for D-AAO from porcine kidney (kd, 5L/h= 0.0108 and kd, 10L/h=0.0198 min-1).