Intra-enzyme and mediator cross-reaction electron-transfer reaction kinetics of sulfite oxidase

Abstract

At saturating concentrations of sulfite, the consumption of electron-transfer mediator-oxidants by reaction with the heme site of sulfite oxidase is governed, at low turnover rates, by the mediator-heme electron-transfer cross-reaction rate and, at high turnover rates, by that of the intra-enzyme delivery of electrons from enzyme Mo site to heme site. The mediators employed are cobalt polypyridine complexe and ferricytochrome c. Rate constants (k 12 ) for mediator-heme cross-reactions are shown to depend onthe choice of mediator, whereas rate constants (k in ) for the intra-enzyme reaction do not