Inactivation of Bacterial D-Amino Acid Transaminase by fi-Chloro-D-alanine*

Purified D-amino acid transaminase from Bacillus sphaericus catalyzes an (~,/3 elimination from the D isomer of pchloroalanine to yield equivalent amounts of pyruvate, chloride, and ammonia; the L isomer of chloroalanine is not a substrate for this transaminase. During the /I elimination there is a synchronous loss in enzyme activity; the Kinact for /I-chloroalanine was estimated to be about 10 PM. The (Yaminoacrylate-Sehiff base intermediate formed after p elimination of chloride ion is probably the key intermediate that partitions between one inactivation event for every 1500 turnovers. In the presence of D-alanine and cu-ketoglutarate, which are good substrates for the transaminase activity of this enzyme, /3-chloroalanine is a potent, competitive inhibitor (K, = 10 PM) with D-alanine and a weak, uncompetitive inhibitor with a-ketoglutarate.