HYDROLYSIS OF SMALL PEPTIDE-SUBSTRATES PARALLELS BINDING OF CHYMOTRYPSIN INHIBITOR 2 FOR MUTANTS OF SUBTILISIN BPN'

Variants of subtilisin BPN' that possess improved specificity towards isoleucine compared with alanine at the P,position of small peptide su bstrates, were analysed for their ability to bind chymotrypsin inhibit or 2. The binding of the inhibitor with isoleucine (wild-type) and wit h alanine as the P-4 residue parallels the hydrolysis of tetrapeptide substrates. There is a linear relationship between the free energy of binding of the transition state of the substrate and the free energy o f binding of the inhibitor with a slope of 2.0. The data suggest that the inhibitor uses predominantly ground state rather than transition s tate binding energy.