The Primary Specificity of α-Chymotrypsin. Acylated Amino Acid Esters with Normal Alkyl Side Chains

The α-chymotrypsin-catalyzed hydrolysis of a series of N-acetyl-L-amino acid esters of the general formula CH3CONHCH[(CH2)nH]CO2CH3, where n=1-6, has been examined. For this series, K0 reaches a minimum and k0 a maximum when n=5. The method of interaction of acylated L-amino acid derivatives with chymo-trypsin is discussed as well as the magnitude of the forces which can be attributed to the side chain. Each additional methylene group up to the optimum number contributes approximately 680-790 cal. to increased substrate binding and 500 cal. toward decreasing the free energy of activation of the rate-determining kinetic step. The data are incorporated into a general correlation between structure and a-chymotrypsin specificity.