The Conformation of Substrates during Hydrolysis at the Active Site of Chymotrypsin

Abstract

Abstract The quasi axial methyl d-hydrocoumarilate compares favorably with methyl N-acetyl-l-phenylalaninate as a substrate for chymotrypsin in contrast to the planar methyl coumarilate and methyl indene-2-carboxylate and the quasi axial methyl indane-2-carboxylate, which are either not substrates or very poor substrates. These results lead to the conclusion that methyl d-dihydroisocarbostyril-3-carboxylate and methyl d-3,4-dihydroisocoumarin-3-carboxylate are in the axial conformation during hydrolysis by chymotrypsin, and that typical open chain substrates, such as methyl N-acetyl-l-phenylalaninate, must assume a conformation at the active site somewhat similar to that of these sterically restricted cyclic analogues. It is further proposed that a hydrogen bond donor (in addition to the hydrophobic binding site) at the active center of chymotrypsin influences the orientation of substrates and site-specific irreversible inhibitors.