title: Properties of ubiquinol oxidase reconstituted from ubiquinol-cytochrome c reductase, cytochrome c and cytochrome c oxidase.
abstract: Ubiquinol-cytochrome c reductase (Complex III), cytochrome c and cytochrome c oxidase can be combined to reconstitute antimycin-sensitive ubiquinol oxidase activity. In 25 mM-acetate/Tris, pH 7.8, cytochrome c binds at high-affinity sites (KD = 0.1 microM) and low-affinity sites (KD approx. 10 microM). Quinol oxidase activity is 50% of maximal activity when cytochrome c is bound to only 25% of the high affinity sites. The other 50% of activity seems to be due to cytochrome c bound at low-affinity sites. Reconstitution in the presence of soya-bean phospholipids prevents aggregation of cytochrome c oxidase and gives rise to much higher rates of quinol oxidase. The cytochrome c dependence was unaltered. Antimycin curves have the same shape regardless of lipid/protein ratio, Complex III/cytochrome c oxidase ratio or cytochrome c concentration. Proposals on the nature of the interaction between Complex III, cytochrome c and cytochrome c oxidase are considered in the light of these results.
mesh_terms: D000968:Antimycin A / Q000031:analogs & derivatives / Q000494:pharmacology; D001665:Binding Sites; D002021:Buffers; D003574:Cytochrome c Group / Q000378:metabolism*; D014450:Electron Transport Complex III; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D009097:Multienzyme Complexes / Q000378:metabolism*; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D010743:Phospholipids / Q000494:pharmacology; D011485:Protein Binding; D011808:Quinone Reductases / Q000378:metabolism*
chemical_list: D002021:Buffers; D003574:Cytochrome c Group; D009097:Multienzyme Complexes; D010743:Phospholipids; C032456:antimycin; D000968:Antimycin A; D009247:NADH, NADPH Oxidoreductases; D011808:Quinone Reductases; D003576:Electron Transport Complex IV; D014450:Electron Transport Complex III