Differential investigation of the capacity of succinate oxidation in human skeletal muscle.

Procedures are described for the estimation of the succinate:ubiquinone oxidoreductase and succinate:phenazine methosulfate oxidoreductase activities in post-nuclear supernatants of human skeletal muscle homogenates using 2,6-dichlorophenol indophenol as the terminal electron acceptor. The influence of ionic strength and of sucrose upon these assays and upon the succinate:cytochrome c oxidoreductase activity has been investigated. Sucrose markedly interferes with the activation of the succinate dehydrogenase complex. Succinate:cytochrome c oxidoreductase activity and succinate:phenazine methosulfate oxidoreductase activity are inhibited by increasing concentrations of ions and of sucrose. Our results lead us to propose the existence of a single acceptor site for phenazine methosulfate at the succinate dehydrogenase complex, not involved in the physiological electron flux across ubiquinone. Estimation of the enzymatic activities mentioned above allows differential investigation of the functional integrity of a large part of the respiratory chain in patients suspected of suffering from a neuromuscular disorder.