The d-amino acid oxidase of Neurospora

Abstract

Among artificially produced mutants of the mold Neurospora have been found strains lacking the ability to synthesize specific amino acids (1, 2). In the course of biochemical and genetic studies of this group of mutants it was observed that some of the mutants, e.g. those deficient in methionine, leucine, and arginine,(1) are able to utilize racemic mixtures of the amino acids with the same efficiency as the l, or physiologically occurring, forms. In the cases of the leucine- and the methionine-requiring mutants it was also possible to show utilization of the ar-keto analogues. It thus appeared possible that the mode of conversion of the d to the l isomers consists in oxidative deammation, followed by resynthesis. A study was therefore undertaken to test the ability of Neurospora to oxidize the “unnatural” optical isomers of the amino acids. It was found that extracts of the mold contain a d-amino acid oxidase similar in its action to the d-amino acid oxidase of mammalian kidney and liver (3). This finding supports the above hypothesis for the conversion of the d- to the l-amino acids. Since it appears that the d-amino acid oxidase has not been previously described in fungi, a number of experiments were performed on the Neurospora enzyme, the results of which are reported here.