Electron Transfer and Spectral Changes in Cytochrome b Studied in Mitochondria from Coenzyme Q-Deficient Mutants of the Yeast Saccharomyces Cerevisiae Reconstituted with Coenzyme Q Analogues
Mitochondria isolated from coenzyme Q-deficient yeast cells had no detectable NADH: or succinate: cytochrome c reductase activity, but contained control amounts of cytochromes b and c 1 by spectral analysis. Addition of the exogenous coenzyme Q derivatives Q2, Q6 and the decyl analogue (DB)1 restored the rate of antimycin-sensitive reductase activity to the levels observed with the wild type. Addition of these same analogues to wild type mitochondria increased 2-3 fold the rate of cytochrome c reduction suggesting that the pool of coenzyme Q in the membrane is limiting for electron transport in the respiratory chain.
Addition of succinate and coenzyme Q to mitochondria from the Q-deficient yeast cells resulted in reduction of cytochromes b and c. The subsequent addition of antimycin resulted in the oxidant-induced extra- reduction of cytochrome b and the concomitant oxidation of cytochrome c without the “red shift” observed in the wild type. Similarly, no “red shift” was observed upon addition of antimycin to dithionite-reduced mitochondria from the mutant cells as was observed with wild type mitochondria. Addition of succinate and antimycin to the Q-deficient mitochondria in the absence of exogenous coenzyme Q analogues led to reduction of 68% of the total cytochrome b again with no shift in the absorption maximum. These results suggest that exogenous coenzyme Q analogues may reconstitute electron flow in mitochondria from Q- deficient yeast cells, but may not be reconstituted into the membrane exactly as is the tightly-bound coenzyme Q reported to be an integral part of the cytochrome b-C 1 complex.
KeywordsRespiratory Chain Reductase Activity Isoprene Unit Yeast Mitochondrion Iron Sulfur Protein
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