EFFECT OF PHOSPHOLIPID ON THE REDOX POTENTIAL AND ENZYMIC PROPERTIES OF CYTOCHROMES-B

The effects of phospholipid on the redox behavior of b cytochromes in succinate-cytochrome c reductase, the cytochrome b-c1 complex, and an isolated cytochrome b preparation were investigated by the oxidative and reductive titrations. Three Em values of cytochrome b were observed in the phospholipid-sufftcient and -depleted succinate-cytochrome c reductase. Their midpoint potentials at pH 7.4 are 75, 75, and -100 mV for the sufficient and 10, -30, and -160 mV for the depleted reductase. The molar distribution of the b cytochromes of these Em values correspond to 30, 30, and 40%, respectively. The Em values of the isolated cytochrome b preparations were not affected by addition of phospholipids. The isolated b preparation contained two components of equal concentration with Em values of -85 and -200 mV. No direct correlation between enzymic activity and the amount of high potential b cytochromes present in the systems was demonstrated. Very little difference was observed in redox behavior of b cytochromes between the aged inactive preparations of phospholipid-depleted reductase and that of freshly prepared reconstitutively active enzyme. © 1979.