Mitochondrial oxidative phosphorylation is defective in the long-lived mutant clk-1

Abstract

The long-lived mutant of Caenorhabditis elegans, clk-1, is unable to synthesize ubiquinone, CoQ9. Instead, the mutant accumulates demethoxyubiquinone9 and small amounts of rhodoquinone9 as well as dietary CoQ8. We found a profound defect in oxidative phosphorylation, a test of integrated mitochondrial function, in clk-1 mitochondria fueled by NADH-linked electron donors, i.e. complex I-dependent substrates. Electron transfer from complex I to complex III, which requires quinones, is severely depressed, whereas the individual complexes are fully active. In contrast, oxidative phosphorylation initiated through complex II, which also requires quinones, is completely normal. Here we show that complexes I and II differ in their ability to use the quinone pool in clk-1. This is the first direct demonstration of a differential interaction of complex I and complex II with the endogenous quinone pool. This study uses the combined power of molecular genetics and biochemistry to highlight the role of quinones in mitochondrial function and aging.