The reconstitution of oxidative phosphorylation in mitochondria isolated from a ubiquinone-deficient mutant ofSaccharomyces cerevisiae

Mitochondria, isolated from the ubiquinone-deficient nuclear mutant ofSaccharomyces cerevisiae E3-24, are practically unable to oxidize exogenous substrates. Respiratory activity, coupled to ATP synthesis, can, however, be reconstituted by the simple addition of ethanolic solutions of ubiquinones. A minimal length of the isoprenoid side chain (3) was required for the restoration. Saturation of the reconstitution required a large amount of exogeneous ubiquinone, in excess over the normal content present in the mitochondria of the wild type strain. A similar pattern of reconstituted activities could be also obtained using sonicated inverted particles. Mitochondria and sonicated particles are also able to carry out a dye-mediated electron flow coupled to ATP synthesis in the absence of added ubiquinone, using ascorbate or succinate as electron donor. This demonstrates that the energy conserving mechanism at the third coupling site of the respiratory chain is fully independent of the presence of the large mobile pool of ubiquinone in the membrane.