Arrangement of the electric potential-generating redox chain in the mitochondrial membrane.

Abstract

The intramembrane arrangement of the respiratory chain generating electric potential difference across the mitochondrial membrane has been studied. The accessibility of various respiratory carriers to the non-penetrating electron donors and acceptors, such as ferri-and ferrocyanide, cytochrome c. fumarate and nicotinamide nuclcotides has been used as a test for surface localization of the carrier in the membrane of mitochondria and “inside-out” (sonicated) submitochondrial particles. Membrane potential formation was detected by measuring the transmembrane flows of the penetrating anion, phenyl dicarbaundecaborne (PCB−). It is shown that ferricyanide reduction can support PCB− movement if this electron acceptor interacts with intact mitochondria in the region localized on the oxygen site of the antimycin-sensitive point. The same region is accessible for ferrocyanide whose oxidation by O2 can be also coupled with PCB− translocation. Added nicotinamide nuclcotides cannot be utilized by mitochondria for supporting PCB− movement. PCB− movement in the “inside-out” submitochondrial particles can be supported by reduction of ferricyanide or fumarate by NADH, and of NAD+ by NADPH, the former process being sensitive to rotenone but not to antimycin. Antimycin-insensitive reduction of feericyanide or of CoQ6 by succinate is not coupled with PCB− transport. Neither ferrocyanide nor ferrocytochromec can be used as electron donors in the particles. Penetrating electron donors (TMPDH2, succinate) and acceptors (menadione) are effective both in mitochondria and particles. It is coucluded that flavin and transhydrogenase regions of the potential-generating redox chain are localized near the inner surface, cytochromec region-near the outers surface of the internal membrane of intact mitochondria. It means that the redox chain includes at least one act of the transmembrane transfer of reducing equivalents between flavins and cytochromec.