PMID: 8294431Jan 21, 1994

Membrane potential-linked reversed electron transfer in the beef heart cytochrome bc1 complex reconstituted into potassium-loaded phospholipid vesicles.

The Journal of Biological Chemistry
T MikiY Orii


The cytochrome bc1 complex purified from beef heart mitochondria was incorporated into potassium (K+)-loaded phospholipid vesicles by a cholate dialysis method to study the reverse reaction of electron transfer in the complex. The reduction of cytochrome b in the presence of sodium ascorbate was observed on addition of valinomycin to the K(+)-loaded proteoliposomes in a medium containing no external KCl; it was followed by the gradual oxidation. Nigericin accelerated the reoxidation of reduced cytochrome b, indicating that a K+ diffusion potential (negative inside) induced the reduction of cytochrome b. The extent of the cytochrome b reduction depended on the magnitude of the diffusion potential across the liposomal membranes, and its maximal reduction was attained at more than 210 mV of the diffusion potential. It was cytochrome b562 that was reduced during the establishment of the K+ diffusion potential in the presence of ascorbate, and about 90% of cytochrome b562 was estimated to be reduced. Antimycin A and myxothiazol inhibited the diffusion potential-induced reduction of cytochrome b562, and ubiquinone was proved to be essential for the reversed electron transfer. The K+ diffusion potential also induced the partial reduct...Continue Reading

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