STEREOCHEMISTRY OF CONVERSION OF THE SUICIDE SUBSTRATES BETA-CHLORO-D-ALANINE AND D-SERINE AND L-SERINE O-SULFATES INTO PYRUVATE BY D-AMINO-ACID AMINOTRANSFERASE AND BY L-ASPARTATE AMINOTRANSFERASE

beta-Chloro-D-alanine and D-serine O-sulfate are converted into a puta tive aminoacrylate intermediate by D-amino acid aminotransferase. This either reacts with pyridoxal phosphate to form a reactive inhibitor o f the enzyme or it is protonated and hydrolysed to give pyruvate. The protonation reaction is shown to occur with modest stereoselectivity. indicating overall retention of stereochemistry in replacement of the leaving group by hydrogen. The corresponding reaction of L-serine O-su lfate using L-aspartate aminotransferase shows little or no stereosele ctivity.