The role of entropy and enthalpy factors in kinetic specificity of α-chymotrypsin: Temperature dependence study of acyl-α-chymotrypsins deacylation

Abstract A temperature study has been made for deacylation of intermediate acyl enzymes formed in the α-chymotryptic hydrolysis of p -nitrophenyl carboxylates. H(CH 2 ) n C(O)OC 6 H 4 NO 2 , with n varying from 1 to 7. Activation parameters, ΔH 3 ≠ , and Δ S 3 ≠ , for α-chymotryptic hydrolysis of a number of N- acetyl- l -amino acid methyl esters are also reported. The following results are discussed: 1. 1. Hydrolysis of acylenzymes, RCH(NHCOCH 3 )C(O)-enzyme and RCH 2 C(O)-enzyme, containing the same R group in the substrate moiety proceeds with an almost similar enthalpy of activation. The difference in ΔS 3 ≠ for such pairs of acylenzymes with or without N -acetyl group in the substrate moiety is about 12 cal/degree per mole. 2. 2. For acyl-α-chymotrypsins with various side chains R a linear relationship has been found to exist between the enthalpy and the entropy of activation for deacylation reaction, the straight lines which refer to both series of acylenzymes being almost parallel and having a slope of about 420 °K. These data are used to interpret some new aspects of kinetic specificity of α-chymotrypsin.