The Subunit Composition of Sweet Potato Cytochrome b-c₁ Complex

Abstract

Attempts to solubilize active ubiquinol : cytochrome c reductase, cytochrome b-c₁ complex, from the submitochondrial particles from sweet potato root tissue ended in failure because all detergents tested caused inactivation of this enzyme complex. Consequently, the complex was isolated with the content of cytochrome b as the marker for purification after solubilization with deoxycholate though it was inactive. Deoxycholate had no effect on two α-bands at 555 and 558nm but caused a blue shift of an α-band at 563nm in the reduced-minus-oxidized difference spectrum of the submitochondrial particles at low temperature. The purified complex exhibited the same difference spectra at low and room temperatures as the submitochondrial particles in the presence of deoxycholate, which suggests that the complex has three (at least two) cytochrome b components with different spectroscopic properties and that the apparent molar ratio of cytochrome b to c₁ is 1.5. The purified complex consisted of eight subunits: I, 51kDa ; II, 49kDa ; III, 33kDa ; IV, 32kDa ; V, 27kDa ; VI, 17kDa ; and VII and VIII, 10kDa. Subunits III and IV were cytochrome c₁ and b, respectively.