Properties of ubiquinol oxidase reconstituted from ubiquinol-cytochrome c reductase, cytochrome c and cytochrome c oxidase

• Published in: Biochemical journal 1982-02, Vol.202 (2), p.527-534
• Main Authors: Diggens, R J, Ragan, C I
• Format: Article
• Language: English
• Subjects: Antimycin A - analogs & derivatives; Antimycin A - pharmacology; Binding Sites; Buffers; cytochrome c; Cytochrome c Group - metabolism; cytochrome c oxidase; Electron Transport Complex III; Electron Transport Complex IV - metabolism; Hydrogen-Ion Concentration; Multienzyme Complexes - metabolism; NADH, NADPH Oxidoreductases - metabolism; Phospholipids - pharmacology; Protein Binding; Quinone Reductases - metabolism; ubiquinol-cytochrome c reductase
• ISSN: 0264-6021; 0306-3283; 1470-8728
• DOI: 10.1042/bj2020527

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.