SUBUNIT STRUCTURES OF PURIFIED BEEF MITOCHONDRIAL CYTOCHROME BC(1) COMPLEX FROM LIVER AND HEART

The existence of tissue-specific isozymes of cytochrome c oxidase has been widely documented. We have now studied if there are differences b etween subunits of mitochondrial bc1 complexes isolated from liver and heart. For this purpose, we have developed a method for the purificat ion of an active ubiquinol-cytochrome c oxidoreductase from adult bovi ne liver that includes solubilization of submitochondrial particles wi th deoxycholate, ammonium acetate fractionation, resolubilization with dodecyl maltoside, and ion exchange chromatography. The electrophoret ic pattern of the liver preparation showed the presence of 11 subunits , with apparent molecular weights identical to the ones reported for t he heart complex. Western blot analysis and isoelectric focusing follo wed by two-dimensional gels of bc1 complexes from liver and heart were compared, and no qualitative differences were observed. In addition, the high-molecular-weight subunits of the purified complexes from both tissues, subunits I, II, V, and VI, were isolated by PAGE in the pres ence of Coomasie Blue and subjected to limited proteolysis and to chem ical digestion with cyanogen bromide and BNPS-skatol, and the peptide patterns were compared. Finally, two of the small-molecular-weight sub units from the liver complex were isolated (subunits VII and X), parti ally analyzed by amino terminal sequencing, and found to be identical with the reported sequence of their heart counterparts. The data sugge st that, in contrast to the case of cytochrome c oxidase, bc1 complexe s from liver and heart do not exhibit tissue-specific differences.