HYDROPHOBIC INTERACTIONS OF SOME ALCOHOLS WITH ACYL TRYPSINS

The variation of the apparent reactivity of added nucleophiles competing with water in the deacylation of some acyltrypsins has been studied with different ester substrates: Lysine ethyl and methyl ester, arginine methyl ester and α-N-carbobenzoxy-l-lysine p-nitrophenyl ester. The efficacy of the primary aliphatic alcohols increases with the length of the apolar chain. For instance, the reactivity of heptanol toward lysyl trypsin is about 45 times greater than that of ethanol. These data cannot be explained merely in terms of the chemical reactivity of the alcohols. It is necessary to assume that water as well as the aliphatic primary alcohols used as nucleophiles interact with a corresponding site of the enzyme. The apparent reactivity of nucleophilic compounds is interpreted in terms of hydrophobic interactions between an apolar site of the acyl enzyme and the hydrocarbon chain of the alcohols. Results obtained with organic solvents such as dimethyl-formamide and isopropanol, an unreactive alcohol, are in good agreement with such an interpretation. © 1969.