Mitochondria were isolated from wild type, respiratory deficient cor1 null mutant, Q-less coq3 null mutant, Q-replete coq10 null mutant and coq10 null mutant harboring plasmids expressing the designated proteins. NADH-cytochrome c reductase activity was determined in the absence (white bars) or presence (black bars) of 1 μM coenzyme Q2 (performed in triplicate for each sample). NADH-cytochrome c activity of the yeast coq3 null mutant, coq10 null mutant and coq10 null mutant expressing empty vector and V70K is significantly rescued by the addition of 1 μM coenzyme Q2; a, p < 0.0175; b, p < 6.1 E−04; c, p < 3.3 E−03. Values are given as the average ± standard deviation.