Role of coenzyme Q in the mitochondrial respiratory chain. Reconstitution of activity in coenzyme Q deficient mutants of yeast

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Abstract
The reduction of cytochrome c by the reduced form of the 6-decyl analog of coenzyme Q [Saccharomyces cerevisiae] follows 1st-order kinetics with respect to cytochrome c and increases in a linear manner with added mitochondrial protein. The activity is completely sensitive to antimycin A in whole cell extracts of yeast and in isolated mitochondria and fractionates with markers for the mitochondrial electron-transport chain. The presence of both cytochrome b and c1 in an approximately 2:1 ratio appears essential for enzymatic activity. Reduced coenzyme Q:cytochrome c reductase obeys Michaelis-Menten kinetics when assayed in mitochonrida obtained from a yeast strain lacking coenzyme Q. Both reduced NADH and succinate:cytochrome c reductase activities were not detectable in 6 coenzyme Q deficient strains tested, but were restored after addition of the oxidized form of the coenzyme Q analog. No marked difference in the concentration of the analog required to restore the 2 activities was observed.