Stereochemistry and Mechanism of Reactions Catalyzed by Tryptophanase from Escherichia coZi*

Several p replacement and cu,p elimination reactions catalyzed by tryptophanase from Escherichia coli are shown to proceed stereospecifically with retention of configuration. These conversions include synthesis of tryptophan from (2S,3R)- and (2S,3S)-[3-3H]serine in the presence of indole, deamination of these serines in DzO to pyruvate and ammonia, and cleavage of (2S,3R)-and (2S,3S)-[3-3H]tryptophan in DzO to indole, pyru-vate, and ammonia. A coupled reaction with lactate dehydrogenase was used to trap the stereospecifically labeled [3-H,2H,SH]pyruvates as lactate, which was ox-idized to acetate for chirality analysis of the methyl group. During deamination of tryptophan there is sig-nificant intramolecular transfer ‘of the (Y proton of the amino acid to C-3 of indole