The oxidation of L-amino acids by Mytilus edulis

L-Amino acid oxidases from microbial sources: types, properties, functions, and applications

L-Amino acid oxidases (LAAOs), which catalyze the stereospecific oxidative deamination of L-amino acids to α-keto acids and ammonia, are flavin adenine dinucleotide-containing homodimeric proteins. L-Amino acid oxidases are widely distributed in diverse organisms and have a range of properties. Because expressing LAAOs as recombinant proteins in heterologous hosts is difficult, their biotechnological applications have not been thoroughly advanced. LAAOs are thought to contribute to amino acid catabolism, enhance iron acquisition, display antimicrobial activity, and catalyze keto acid production, among other roles. Here, we review the types, properties, structures, biological functions, heterologous expression, and applications of LAAOs obtained from microbial sources. We expect this review to increase interest in LAAO studies.

Advances in non-snake venom L-amino acid oxidase

L-amino acid oxidase is widely found in diverse organisms and has different properties. It is thought to contribute to antimicrobial activity, amino acid catabolism, and so forth. The purpose of this communication is to summarize the advances in non-snake venom L-amino acid oxidase, including its enzymatic and structural properties, gene cloning and expression, and biological function. In addition, the mechanism of its biological function as well as its application is also discussed.

The oxidation of lysine and oxalysine by Mytilus edulis: Identification of the products formed in the presence and the absence of catalase

1. O-(2-Aminoethyl)serine (oxalysine) was shown to be a substrate of the l-amino acid oxidase of the digestive gland of the common mussel, Mytilus edulis. 2. Three atoms of oxygen were consumed per mole of oxalysine oxidized in the presence of catalase; l-lysine under the same conditions consumed only one atom. 3. The products of oxidation of oxalysine in the presence and the absence of catalase were: ethanolamine, N-oxalylethanolamine and 3-morpholone (the oxygen analogue of 2-piperidone). After acid hydrolysis 70% of the oxalysine oxidized was recovered as ethanolamine. 4. In the absence of catalase 2-aminoethoxyacetic acid was also detected. 5. The products identified account quantitatively for the oxalysine oxidized and for the oxygen uptake. 6. N-Oxalylethanolamine and 2-aminoethoxyacetic acid have been synthesized. 7. Treatment of extracts of the digestive gland at pH3.0 completely inactivated the catalase, leaving the l-amino acid oxidase unaffected. 8. The major product of the oxidation of lysine in the absence of catalase was 2-piperidone.

Partial amino acid sequence of an L-amino acid oxidase from the cyanobacterium Synechococcus PCC6301, cloning and DNA sequence analysis of the aoxA gene

A novel type of L-amino acid oxidase from Synechococcus PCC6301 was purified and subjected to amino acid sequence analysis. Since the N-terminus of the L-amino acid oxidase protein was not accessible for Edman degradation, the protein was partially hydrolysed and a contiguous sequence of 17 amino acid residues was obtained from an endogenous peptide fragment. Based on the partial peptide sequence two oligonucleotides were designed, which were used as probes in Southern hybridization experiments in order to identify the corresponding aoxA gene. The aoxA gene was isolated from a size-fractionated genomic library of Synechococcus PCC6301 and subsequently sequenced. From the nucleotide sequence (data base accession number Z48565) it can be deduced that the L-amino acid protein consists of 355 amino acid residues resulting in a molar mass of 39.2 kDa. The calculated isoelectric point of the protein is 9.81. The L-amino acid oxidase from Synechococcus PCC6301 shows low homologies to other flavin oxidases/dehydrogenases, especially amine oxidases, but no homologies to other so far sequenced L- or D-amino acid oxidases.

Purification and characterization of an L-amino-acid oxidase from Chlamydomonas reinhardtii

An L-amino-acid oxidase (EC 1.4.3.1) that catalyzes the oxidative deamination of twelve L-amino acids has been purified 21-fold and with 14% yield to electrophoretic homogeneity from Chlamydomonas reinhardtii cells by ammonium-sulfate fractionation, gel filtration through Sephacryl and Superose, anion-exchange chromatography and preparative electrophoresis in polyacrylamide gels. The native enzyme is a protein of 470 kDa and consists of eight identical or similarsized subunits of 60 kDa each. Optimum pH and temperature were 8.2 and 55° C, respectively, with a Q10 (45-55° C) of 1.7 and an activation energy of 45 kJ · mol(-1). Its absorption spectrum showed, in the visible region, maxima at 360 and 444 nm, characteristic of a flavoprotein with a calculated flavin content of 7.7 mol FAD per mol of native enzyme. Apparent K m values of the twelve L-amino acids which can act as substrates of L-amino-acid oxidase ranged between 31 μM for phenylalanine and 176 μM for methionine. The effect of several specific group reagents, chelating agents and bivalent cations on enzyme activity has also been studied.

A novel L-glutamate oxidase from Streptomyces endus. Purification and properties

A new flavoenzyme using molecular oxygen to oxidize L-glutamic acid has been purified to homogeneity, as judged by polyacrylamide gel electrophoresis, from the culture medium of Streptomyces endus. Hydrogen peroxide, 2-oxoglutaric acid and ammonia are formed as products. Among 25 amino acids tested including D-glutamic acid, L-glutamine and L-aspartic acid, only L-glutamic acid is converted. The molecular mass of the enzyme was estimated to be about 90 kDa by gel chromatography and 50 kDa by SDS/PAGE. The subunit contains 1 molecule noncovalently bound FAD. The absorption spectrum shows maxima at 273, 355 and 457 nm and the isoelectric point is at pH 6.2. The Km value for L-glutamic acid in air-saturated phosphate pH 7.0 was estimated to be 1.1 mM, the Km for oxygen was calculated to be 1.86 mM at saturating concentration of L-glutamic acid. The enzymic reaction is inhibited by Ag+ and Hg2+ ions. The enzyme described here distinctly differs from two microbial L-glutamate oxidases purified hitherto, with regard to extremely high substrate specificity and to the subunit structure.

Purification and characterization of L-amino acid oxidase from the venom of Trimeresurus mucrosquamatus (Taiwan habu snake)

L-Amino acid oxidase (EC.1.4.3.2) was purified to homogeneity via four steps consisting of Sephadex G-100, CM-Toyopearl 650M, and first and second granulated hydroxyapatite column chromatographies. The mol. wt of the enzyme was 140,000 when estimated by analytical gel filtration and was 70,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, suggesting that the enzyme is composed of two identical subunits. The enzyme has an absorption spectrum characteristic of flavoprotein, contains 2 moles of FMN per mole of enzyme and has an isoelectric point of 5.4. The enzyme oxidatively deaminated hydrophobic amino acids such as Leu, Met, Phe, and Tyr while basic amino acids except for Lys were also oxidized though at slower rates. This specificity was generally similar, with some exceptions, to that of the enzyme from Trimeresurus flavoviridis venom. For oxidative deamination of Leu, Km and maximum velocity of the enzyme were 1.17 mM and 9.9 units/mg, respectively, at pH 7.6. The activity was inhibited almost completely by heavy metal ions, some aromatic benzoates and sulfhydryl reagents but not by metal-chelating agents.

l-amino acid oxidases of Proteus rettgeri

Proteus rettgeri has been found to contain two separable 1-amino acid oxidases. Both enzymes are particulate in nature, neither being ribosomal bound. One of these enzymes appears to have broad specificity, being active toward monoaminomonocarboxylic, imino, aromatic, sulfur-containing, and beta-hydroxyamino acids. The other enzyme has more limited specificity, catalyzing the oxidative deamination of the basic amino acids and citrulline. The affinity of this oxidase for the various substrates at pH 7.6 in decreasing order is arginine, histidine, ornithine, citrulline, and lysine. This enzyme has a particularly high affinity for arginine (Km equal to 0.27 mM), and anomalous kinetics are observed with increasing substrate concentrations. When concentrations of arginine greater than 1.0mM were added to the reaction containing histidine, imidazole pyruvate formation was completely inhibited.