Electrostatic effects in the alpha-chymotrypsin-catalyzed acyl transfer. I. Influence of different inorganic salts.

We investigated the deacylation of two acyl-alpha-chymotrypsins by added nucleophiles. The nucleophile binding site of the enzyme shows a strong preference for positively charged compounds. Most of our data can be explained by direct electrostatic interaction between the ionic nucleophiles and two negatively charged residues which are located close to the active site of the enzyme molecule. The influence of inorganic salts on the acyl transfer includes the following effects: (1) reduction of electrostatic interactions between the acyl-enzyme and the nucleophile by addition of salts; (2) binding of divalent cations to the nucleophile binding site of the acyl-enzyme leading to a significantly changed specificity; and (3) linear dependence of the activity coefficients of the added nucleophiles on salt concentration.