Biochemical and Immunological Investigation of Quinol-Cytochrome c Reductase

Sammanfattning: In order to understand the mechanism of electron and proton transport within mitochondrial ubiquinol-cytochrome c reductase (Complex III), we have undertaken a biochemical and immunological investigation regarding the structure, function and topology of its subunits. A major part of this investigation deals with the two largest subunits, the so-called core proteins, which make up approximately 50 percent of the total Complex III protein. Based on a comparison of Complex III from different sources, and by the specific localization of subunits I, II, V, VI and VII to Complex III by immunological methods, we suggest that all subunits of the isolated enzyme are specific members of Complex III. Complex III from different tissues was found, by immunological methods, to be very similar. An extensive homology was also found between the core proteins from beef and rat. A stoichiometry of one mole core protein I, two moles core protein II, two moles cytochrome b and one mole cytochrome c was found per mole Complex III. The core proteins were localized to the matrix side of the mitochondrial inner membrane. Modification of fire core proteins by partial proteolysis or antibody binding had no effect on NADH oxidase activity or respiratory control in submitochondrial particles, pl values of 6,3 and 8,5 were obtained for core protein I and core protein II, respectively.