Deamination of serine. II. D-Serine dehydrase, a vitamin B6 enzyme from Escherichia coli.

Non-enzymatic deamination of serine and cysteine is catalyzed by pyridoxal and certain metal salts at 100” (2). This finding suggested that pyridoxal phosphate might be involved in the enzymatic deamination of these amino acids. Vitamin B, has already been implicated in the desulfhydration of cysteine by rat liver (3) and of cysteine and homocysteine by bacteria (4). Several similarities of cysteine desulfhydrase and of serine dehydrase have been reported (5, 6). These findings supported the supposition that vitamin Be might be involved in serine dehydration, in spite of the recent report that adenosine-5-phosphate and glutathione are the only demonstrable cofactors of serine and threonine dehydrases (deaminases) from Escherichiu c& (7). The preparation in cell-free form of a pyridoxal phosphate (PLP) requiring n-serine dehydrase from cells of E. coli is described below. This enzyme is readily separated from the serine dehydrase of Wood and Gunsalus (7), which appears to be an L-serine dehydrase.