Interactions of alpha-chymotrypsin with peptides containing tryptophan or its derivatives at the C-terminus

The interaction between alpha-chymotrypsin [EC 3.4.21.1] and peptide substrate or peptide inhibitor was investigated to determine how the secondary interaction influences the rate of hydrolysis or the binding and whether or not its effect is variable with alteration of the P1 residue which interacts with the specificity determining site of the enzyme. Kinetic analysis was carried out at pH 6.5 and 7.8 for substrates of the type Ac-Glyn-X-OMe and for inhibitors of the type Ac-Glyn-X-OH where X denotes tryptophan or its derivatives. With substrates containing tryptophan or Nin-formyltryptophan, the second-order rate of hydrolysis increases with increase of chain length. With substrates containing 2-(2-nitro-4-carboxyphenylsulfenyl)-tryptophan, however, the rate of hydrolysis decreases with elongation of the chain, due to an increase in Km(app). The corresponding inhibitors behave differently from the other series of inhibitors at pH 6.5. The results indicate that the influence of the secondary interaction on reactivity or binding is related to the structural features of the P1 residue.