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

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.