Oxalacetic oxidase

Further evidence of like character in support of the participation of coenzyme I in reactions associated with the reduction of dehydroascorbic acid has been advanced by Waygood (1950). Cell-free extracts of wheat seedlings were found to contain a malic dehydrogenase enzyme, reducing coenzyme I, as well as ascorbic oxidase and peroxidase enzymes. When to such extracts malic acid, coenzyme I, and ascorbic acid were added, together with a fixative for the oxalacetate formed in the reaction, the system absorbed oxygen in excess of that required for the complete oxidation of ascorbic acid. In this system methylene blue could replace ascorbic acid. 

Malie Oxidase. Recently another enzymatic mechanism for oxidizing malate was discovered in Micrococcus lysodeikticus. The chemical nature of this enzyme has not been determined as yet, but it does not use p3rridine nucleotides. Ferricyanide was used as the electron acceptor, and in the reaction oxalacetate accumulated. Evidence for a similar activity has also been found in extracts of pigeon liver. 

Ti-Aspartic Oxidase. Aspartase and transaminases account for a major part of the metabolism of L-aspartic acid. n-Aspartic acid is oxidized by an enzyme present in liver and kidney. This is an oxidase that converts aspartate to oxalacetate and ammonia while reducing oxygen to hydrogen peroxide. The oxidase was resolved by ammonium sulfate precipitation and dialysis to a protein that could be reactivated by FAD but not by FMN. The enzyme differs from n-amino acid oxidase in its insensitivity to benzoate. The only other known substrate for the partially purified D-aspartic oxidase is D-glutamate, but since the relative rates of oxidation of the two amino acids vary during the preparation of the enzyme, it is... 

D-Aspariic Acid Oxidase. Still et al. reported that rabbit kidney and liver contain a soluble enzyme which catalyzes the aerobic oxidation of D-aspartate to oxalacetate plus NH3 with the formation of hydrogen peroxide. In a later study by Still and Sperling the D-aspartic acid oxidase was resolved and reactivated by the addition of FAD. The purified enzyme showed about one-sixth the activity with D-glutamate this, according to these workers, is best explained by the presence of a D-glu-tamic acid oxidase. The activity of n-aspartic acid oxidase is higher than that of D-amino acid oxidase in rabbit kidney and liver, and they are of the same order of activity in pig kidney. In contrast to pig kidney o-amino acid oxidase, which is inhibited by benzoic acid, the D-aspartic acid oxidase was unaffected. 

There a number of cases other than those of dihydroxyfumaric acid oxidase and tryptophan oxidase in which peroxidases appear to play the part of oxidases. These include indolylacetic acid oxidase and the related indolylpropionic and indolylbutyric acid oxidases (285, 415,416,618,733,777), the oxidase of oxalic, oxalacetic, ketomalonic, and dihydroxytartaric acids (414), of phenylacetaldehyde (413) and saturated fatty acid oxidase (711). 

Manganous ions activate peroxidase as an oxidase toward oxalate, oxalacetate, ketomalonate, and dihydroxytartrate. A peroxidase substrate is necessary for the reaction with the first two substrates, but not for the last two. These reactions depend upon the presence of peroxide. They can be facilitated by adding peroxide, or inhibited by adding catalase, but it is uncertain whether they are instances of direct oxidase action, or of peroxidatic activity (414). 

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