Stereochemistry of the formation of cysteine by O-acetylserine sulfhydrase.

The enzymatic preparation of (2S, 3R)- and (2S, 3S)-[3-3H] serine from the corresponding stereospecifically tritiated 3-P-glycerates is described. Following conversion into T-acetylserine, these substrates were used to establish the steric course of the O-acetylserine sulfhydrase reaction. The two samples of cysteine formed in this reaction were analyzed for their configuration at C-3. The results indicate that the replacement of the acetoxy by a sulfhydryl group in the O-acetylserine sulfhydrase reaction occurs with retention of configuration at carbon atom 3.