Transient-phase studies of a trypsin-catalyzed reaction

Abstract

The stopped-flow technique has been used to study the pre-steady-state kinetics of the hydrolysis of N-carbobenzoxy-L-alanine-p-nitrophenyl ester catalyzed by trypsin. By working under conditions such that the enzyme concentration is much greater than that of the substrate, it has been possible to measure [Formula: see text] the rate constant for the conversion of the enzyme-substrate complex into the acyl enzyme. The pH dependence of [Formula: see text] reveals a pKb′ value of 6.9 for the conversion of complex into acyl enzyme, in agreement with deductions from steady-state investigations. The pH dependence of [Formula: see text] (equal to k−1 + k2)/k1) has also been determined. The results provide direct evidence for the existence of an enzyme-substrate complex for this reaction.The work has been done in various mixtures of water and isopropyl alcohol. The logarithms of the rate constants [Formula: see text] and [Formula: see text] vary linearly with 1/D, showing a decrease with increasing alcohol concentration; [Formula: see text] increases with alcohol concentration. The solvent results suggest that addition of alcohol affects the hydrophobic bonding in the protein and leads to unfolding of the enzyme.