Amino acid oxidases, reactions involving

The reaction is markedly accelerated by the addition of ammonia leads to the formation of the N Mabeled amino acid and spectrophoto-metric studies show that the reduced amino acid oxidase can be reoxidized anaerobically by the addition of ammonia and a-keto acid. All oi these experiments indicate that the reaction observed does not involve a transamination. It has been suggested that imder appropriate phyinological conditions a reversal of the amino acid oxidase reaction may be responsible for amino acid synthesis. 

L-Amino acid oxidase has been used to measure L-phenylalanine and involves the addition of a sodium arsenate-borate buffer, which promotes the conversion of the oxidation product, phenylpyruvic acid, to its enol form, which then forms a borate complex having an absorption maximum at 308 nm. Tyrosine and tryptophan react similarly but their enol-borate complexes have different absorption maxima at 330 and 350 nm respectively. Thus by taking absorbance readings at these wavelengths the specificity of the assay is improved. The assay for L-alanine may also be made almost completely specific by converting the L-pyruvate formed in the oxidation reaction to L-lactate by the addition of lactate dehydrogenase (EC 1.1.1.27) and monitoring the oxidation of NADH at 340 nm. 

Historically, individual enzymes were identified using the name of the substrate or group upon which the enzyme acts and then adding the suffix -ase. For example, the enzyme hydrolyzing urea was urease. Later, the type of reaction involved was also identified, as in carbonic anhydrase, D-amino acid oxidase, and succinate dehydrogenase. In addition, some enzymes had been given empirical names such as trypsin, diastase, ptyalin, pepsin, and emulsin. 

L-amino acid oxidase is an enzyme involved in amino acid catabolism. It is a flavoprotein-containing enzyme that catalyzes the reaction below, yielding a hydrogen peroxide intermediate. 

Oxidases - Oxidases are enzymes that catalyze the oxidation of a substrate without incorporating oxygen into the product. A two-electron oxidation is usually involved, so the oxygen is converted to H202. Most oxidases utilize either a metal or a flavin coenzyme. D-amino acid oxidases catalyze the following reaction ... 

In the first part of this book devoted to cellular metabolism, it was pointed out that riboflavin is converted to monophosphate and diphosphate, yielding the active coenzymes of a large number of enzymes involved in the cellular oxidation-reduction reaction. As can be expected, the enzyme activity for which these flavoproteins are responsible is decreased in riboflavin deficiency. This has been clearly demonstrated for amino acid oxidase. Extensive studies on the effect of riboflavin deficiency on a large number of proteins have not been carried out but it seems logical to assume that the clinicopathological changes that develop in riboflavin deficiency result from the reduced activity of the flavoprotein enzyme. Yet, many... 

So far, the evidence for the participation of an amino acid oxidase in photosystem II reactions is indirect. First of all, it is present in photosystem II particles which have been highly depleted of protein constituents. Secondly, and more significantly, it responds to many of the reagents which affect photosystem II, e. g. cations, o-phenanthroline, ammonium ions and chlorpromazine as shown here. Our current speculation visualizes an amino acid oxidase bound to the reaction center in such a way that the oxidation-reduction of a substrate substitute or a group on the enzyme constitutes part of the "S"-reactions of photosystem II, whereas the electron acceptor reactions leading to quinone reduction are mainly concerned with the redox reactions of the flavin. Thus, we visualize an enzyme closely bound to the reaction center and active on both "sides of it. So far, our data are compatible with, but do not prove, an involvement of the amino acid oxidase in the redox reactions of photosystem II of A, nidulans. 

Other mechanisms of cysteine catabolism have been reported in animals. One such mechanism involves the metaboUsm of cysteine to mercaptopyruvate in a reaction involving amino acid oxidase [Eq. (5)] or aminotransferase activity [Eq. (6)] ... 

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