The interaction between mitochondrial NADH-ubiquinone oxidoreductase and ubiquinol-cytochrome c oxidoreductase. Restoration of ubiquinone-pool behaviour

Abstract

1. In the inner mitochondrial membrane, dehydrogenases and cytochromes appear to act independently of each other, and electron transport has been proposed to occur through a mobile pool of ubiquinone-10 molecules [Kröger & Klingenberg (1973) Eur. J. Biochem. 34, 358–368]. 2. Such behaviour can be restored to the interaction between purified Complex I and Complex III by addition of phospholipid and ubiquinone-10 to a concentrated mixture of the Complexes before dilution. 3. A model is proposed for the interaction of Complex I with Complex III in the natural membrane that emphasizes relative mobility of the Complexes rather than ubiquinone-10. Electron transfer occurs only through stoicheiometric Complex I-Complex III units, which, however, are formed and re-formed at rates higher than the rate of electron transfer.

The effects of lipid phase transitions on the interaction of mitochondrial NADH–ubiquinone oxidoreductase with ubiquinol–cytochrome c oxidoreductase

“…2 do not have very different shapes (for the reasons given above), clearer evidence for restoration of 'Q-pool' behaviour was obtained from titrations performed in the presence of rotenone. As shown by and Heron et al (1978), rotenone decreases the Km for Complex III during 'Q-pool' behaviour, but has no effect in the shape of titration curve obtained in the absence of 'Q-pool' behaviour. This is clearly shown in the experiments of Fig.…”

“…The present paper describes experiments similar to those reported previously Heron et al, 1978), except that endogenous phospho-lipids were replaced by 1,2-ditetradecanoyl-snglycero-3-phosphocholine. …”

“…Theoretical Km values were calculated from V1 and V3, the maximum activity of the Complex III, as described by Heron et al (1978), and compared with the experimental value. This treatment was based on the original description of 'Q-pool' behaviour by Kroger & Klingenberg (1973a,b …”

“…Restoration of' Q-pool' behaviour Supplementation of mixtures of Complex I and Complex III with soya-bean phospholipid and ubiquinone-10 was performed exactly as described by Heron et al (1978 . Theoretical Km values were calculated from V1 and V3, the maximum activity of the Complex III, as described by Heron et al (1978), and compared with the experimental value.…”

“…Arising from studies on the interaction between purified Complex I and Complex III (ubiquinolcytochrome c oxidoreductase; Hatefi et al, 1962b) we have proposed that in the natural membrane, rapidly reversible association of these enzymes into stoicheiometric Complex I-III units takes place Heron et al, 1978). Electron transfer from Complex I to Complex III takes place through these units, and the relative mobility of the separate Complexes in the dissociated state is the basis of 'Q-pool' behaviour as originally described by Kroger & Klingenberg (1973a,b).…”