Kinetics of ubiquinone reduction by succinate in electron transport particles

Abstract

The reduction of ubiquinone (Q) in electron transport particles from beef heart, caused by succinate in the presence of the respiratory inhibitors Antimycin A and eyanide, appears to follow mixed zero- and first-order kinetics of the type expected for a simple enzymic reaction. The zero-order rate for Q reduction is the same in the presence of Antimycin A or cyanide, and is the same as that for cytochrome c reduction in the presence of cyanide and cytochrome b reduction in the presence of Antimycin A for equal numbers of electrons transported. The half-time for Q reduction is at least four times greater than that for the cytochromes under comparable conditions. A simple, approximate method was used to calculate K m for Q in the reduction reaction, assuming that the reaction follows simple Michaelis-Menten kinetics and that the Q is “dissolved” and uniformly distributed in the lipid phase of the particles. The calculated value approximates 1 mm.