Stereochemistry of the reaction of the inhibitor beta-chloroalanine with mercaptoethanol, a beta-substitution reaction catalysed by an aminotransferase

L-Aspartate aminotransferase, a member of the alpha-family of PLP mediated enzymes, which normally catalyses transamination, has been used to catalyse the beta-substitution reaction of stereospecifically labelled samples of t he enzyme inhibitor beta-chloro-L-alanine with 2-mercaptoethanol; the stere ochemistry of the products was assigned by independent synthesis, showing t hat the abnormal substitution reaction proceeds with overall retention of s tereochemistry, the usual stereochemical consequence of reactions catalysed by enzymes of the beta-family of PLP mediated enzymes which have low homol ogy with enzymes of the alpha-family.