Kinetics of the Organic Hydroperoxide-supported Oxidation of Aminopyrine catalyzed by Catalase

Abstract

The kinetic mechanism of the ethyl hydroperoxide (EHP)-and cumene hydroperoxide (CHP)-supported oxidations of aminopyrine catalyzed by catalase was investigated by the use of a stopped-flow spectrophotometer. Plots of reciprocal velocity versus the reciprocal concentration of either substrate at several different fixed concentrations of the other substrate converged to common points of intersection on the left side of the ordinate and above or below the abscissa, suggesting a sequential mechanism involving the formation of a ternary complex between catalase, aminopyrine, and EHP or CHP followed by one or more reactions and the subsequent release of the products. Potassium cyanide was a competitive inhibitor with respect to EHP and non-competitive with respect to CHP and aminopyrine. These results, which indicate that neither CHP nor aminopyrine binds directly to the heme iron, support our previous suggestion that the binding group involved in the CHP-supported oxidation of aminopyrine is different from that for the catalatic reaction.