ENANTIOSPECIFICITY OF ALPHA-CHYMOTRYPSIN AT S1' SITE FOR PEPTIDE-SYNTHESIS IN AQUEOUS-ORGANIC MEDIA

The enantiospecificity of alpha-chymotrypsin (CT) at S1' site in aqueous-organic media was investigated for peptide synthesis from N-acetyl-L-tyrosine ethyl ester (ATEE) as an acyl donor and alanine or serine derivatives a.s acyl acceptors. It was found that catalytic activity of CT is a function of nature of organic solvent, and, among the solvents used, CT exhibited high activity in t-butyl alcohol, acetone, and acetonitrile. The relative reactivity of L-alaninamide as an acyl acceptor to that of D-isomer was also significantly dependent on nature of solvent. CT exhibited high specificity to L-isomer in these three organic solvents. The enantiospecificity is also a function of water content in reaction media. In acetonitrile, the maximum reaction rates of ATEE with L- and D-alaninamide were obtained at 10 and 6% water, respectively, and relative reactivity of D-isomer increased with decrease in water content. Structural effects of acyl acceptors on their reactivity are striking and discussed in terms of stability of their complexes with the acyl-enzyme intermediate.