title: Coenzyme Q analogues reconstitute electron transport and proton ejection but not the antimycin-induced "red shift" in mitochondria from coenzyme Q deficient mutants of the yeast Saccharomyces cerevisiae.
abstract: Mitochondria isolated from coenzyme Q deficient yeast cells had no detectable NADH:cytochrome c reductase or succinate:cytochrome c reductase activity but contained normal amounts of cytochromes b and c1 by spectral analysis. Addition of the exogenous coenzyme Q derivatives including Q2, Q6, and the decyl analogue (DB) restored the rate of antimycin- and myxothiazole-sensitive cytochrome c reductase with both substrates to that observed with reduced DBH2. Similarly, addition of these coenzyme Q analogues increased 2-3-fold the rate of cytochrome c reduction in mitochondria from wild-type cells, suggesting that the pool of coenzyme Q in the membrane is limiting for electron transport in the respiratory chain. Preincubation of mitochondria from the Q-deficient yeast cells with DBH2 at 25 degrees C restored electrogenic proton ejection, resulting in a H+/2e- ratio of 3.35 as compared to a ratio of 3.22 observed in mitochondria from the wild-type cell. Addition of succinate and either coenzyme Q6 or DB to mitochondria from the Q-deficient yeast cells resulted in the initial reduction of cytochrome b followed by a slow reduction of cytochrome c1 with a reoxidation of cytochrome b. The subsequent addition of antimycin resulted in the oxidant-induced extrareduction of cytochrome b and concomitant oxidation of cytochrome c1 without the "red" shift observed in the wild-type mitochondria. Similarly, addition of antimycin to dithionite-reduced mitochondria from the mutant cells did not result in a red shift in the absorption maximum of cytochrome b as was observed in the wild-type mitochondria in the presence or absence of exogenous coenzyme Q analogues.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000968:Antimycin A / Q000031:analogs & derivatives* / Q000494:pharmacology; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D003573:Cytochrome b Group / Q000378:metabolism; D003575:Cytochromes c1 / Q000378:metabolism; D004579:Electron Transport; D007700:Kinetics; D008928:Mitochondria / Q000378:metabolism*; D009154:Mutation; D009245:NADH Dehydrogenase / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D013053:Spectrophotometry; D013384:Succinate Cytochrome c Oxidoreductase / Q000378:metabolism; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000235:genetics / Q000494:pharmacology*
chemical_list: D003573:Cytochrome b Group; C032456:antimycin; D014451:Ubiquinone; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000968:Antimycin A; D003575:Cytochromes c1; D013384:Succinate Cytochrome c Oxidoreductase; D009245:NADH Dehydrogenase