Mutants of Neurospora Deficient in d-Amino Acid Oxidase

Although many investigationshave been carried out on the n-amino acid oxidase since its discovery in 1935 ( 2)) the metabolic role of this enzyme remains somewhat obscure.It is generally believed, on the basis of indirect evidence, that in animals the enzyme functions in the inversion of exogenous n-amino acids over the pathway n-amino acid --+ Lu-keto acid -+ L-amino acid (3).The first step is assumed to be catalyzed by the n-amino acid oxidase, the second by a transaminase.Other functions that have been proposed for the enzyme include the removal of n-amino acids of endogenous origin (4,5) and, in some organisms, the synthesis of n-amino acids (6).It has also been suggested that the enzyme has no physiological significance as a n-amino acid oxidase, but that it is a by-product of metabolism, or that it may have some function other than oxidation of n-amino acids (7,8).Neurospora crassa is known to possess a n-amino acid oxidase which resembles the mammalian enzyme in substrate specificity (5, 9).The evidence suggests that in this organism, too, the enzyme is required for the inversion of o-amino acids of exogenous origin (5).Operating on this assumption, it has been possible to obtain mutants of Neurospora showing little or no n-amino acid oxidase activity.A description of the mutants and their response to n-amino acids is reported below.