D-serine Dehydrase of Neurospora* by Charles Yanofsky

In a previous publication from this laboratory (l), it was mentioned that cell-free extracts of Neurospora mycelium form considerable amounts of pyruvate and ammonia from m-serine. It was also reported that pyridoxal phosphate stimulates the activity of this system. Results similar to these have recently been obtained by Reissig (2). On further examination of the Neurospora system, it has been found that both isomers of serine are deaminated and that in each case pyridoxal phosphate stimulates keto acid production. Since n-serine dehydrase (deaminase) has not been previously studied in a cell-free system, and in view of the apparent participation of pyridoxal phosphate in the react,ion, the characteristics of the Neurospora dehydrase were investigated. There hare been several reports of the deamination of n-serine by organisms other than Neurospora. The n-amino acid oxidase of mammalian tissues oxidatively deaminates D-serine (3); however, Neurospora n-amino acid oxidase does not (4). n-Serine is also rapidly deaminated by rat kidney slices, although in this case the reaction does not appear to be catalyzed by n-amino acid oxidase (5). The product of the deamination of D-serine by rat kidney slices has been identified as &hydroxypyruvic acid (5). There have been several reports of the deamination of n-serine by strains of Bscherichia coli ((6, 7); however, compare Maas and Davis (8)) and, here, pyruvate has been implicated as the probable product of the deamination (7).