Rate enhancement specificity with alpha-chymotrypsin: temperature dependence of deacylation

The relative rate of the hydrolysis of 2-(5-n-alkyl)furoyl-alpha-chymotrypsin reaches a maximum with the propyl derivative. The Arrhenius plots for the hydrolyses of the 2-furoyl-, 2-(5-ethyl)furoyl-, and 2-(5-n-propyl)furoyl-alpha-chymotrypsins display a discontinuity, while the plots obtained with the ramaining furoyl derivatives 5-methyl, 5-n-butyl, and 5-n-amyl are linear. We conclude that the deacylation of the furoyl derivatives of alpha-chymotrypsin involves a minimum of two elementary reaction steps. Depending upon the reaction conditions, rate enhancement specificity appears to be either entropy or enthalpy controlled.