The kinetics of ubiquinone reactions in heart-muscle preparations

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Abstract
Methods for studying the kinetics of endogenous ubiquinone in heart-muscle preparations are described. The rate of reduction of ubiquinone was not equivalent to the steady-state rate of electron transfer as measured by the rate of oxidation of the substrate. Studies with inhibitors indicated that ubiquinone was reduced by the flavoproteins and oxidized by way of the antimycin A-sensitive factor and cytochrome oxidase. It is suggested that ubiquinone is a branch pathway of the respiratory chain, and that it may function either as an interchain carrier or as an intermediate in oxidative phosphorylation.