The stereospecificity of subtilisin BPN′ towards 1-keto-3-carbomethoxy-1,2,3,4-tetrahydroisoquinoline

Like α-chymotrypsin, subtilisin BPN′ reverses its normal stereospecificity when 1-keto-3-carbomethoxy-1,2,3,4-tetrahydroisoquinoline is the substrate; the D-isomer is hydrolyzed readily, the L-isomer is not. However, the enzyme retains its normal stereospecificity when the related open-chain ester N-benzoyl-alanine methyl ester is the substrate; the kinetic constants for hydrolysis of the L-isomer are comparable to those for hydrolysis of other neutral amino acid esters. These results suggest that the stereochemical requirements at the active site of subtilisin BPN′ are similar to those of α-chymotrypsin.