Conformational effect (induced-fit) on catalytic activity of α-chymotrypsin

The kinetics for the hydrolyses of p-nitrophenyl esters of acetic acid and certain amino acid derivatives mediated by alpha-chymotrypsin have been studied. The kinetics are a function of the medium viscosity, which indicate that the enzyme must change its conformation during the reaction. Detailed analysis of the dependence of kinetic rate constants on the medium viscosity has revealed that (1) the reaction is associated with the induced-fit conformational adjustment of the enzyme: When the enzyme-substrate (ES) complex is converted into the corresponding acyl enzyme, the conformation of the enzyme is changed in order to accommodate the acyl group in the pocket of the enzyme at an appropriate position. (2) The conformationally distorted alpha-chymotrypsin recovers its conformation when it releases the acid part of the substrate ester. (3) The formation of an ES complex is independent of any induced-fit movement. The induced-fit conformational adjustment of the enzyme plays a crucial role in its catalytic activity.