Dihydroxyfumaric acid oxidase

In addition to activities ordinarily ascribed to them, peroxidase and catalase possess properties as oxygen transferases and mixed function oxidases. They may exist in functionally active ferrous forms which have, like hemc lobin and myoglobin, the property of combining with molecular oxygen. This oxygen may be transferred to substrate, or be reduced in steps. For purposes of the present review, mechanisms that have been proposed for peroxidatic and catalatic oxidations will be summarized and followed by discussion of dihydroxyfumaric acid oxidase, tryptophan oxidase, and indolyl-acetic oxidase and related oxidases, and indole oxidase. All of these have properties in common with peroxidase and catalase. 

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). 

The study of dihydroxyfumaric acid oxidase thus appears to be the study of a chemical accident. But we are only able to see this as a result of our present understanding of the enzyme. The discrimination between the essential and the fortuitous is wholly dependent upon a prior knowledge of the true and the false. And such knowledge has been in part aggrandized by studying things later proven accidental. 

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