Mg2+ induces intermembrane electron transport by cytochrome c desorption in mitochondria with the ruptured outer membrane

[摘要]

The mechanism of external NADH oxidation in rat liver mitochondria is not clear yet, but it evidently includes the intermembrane electron transport (IMET). We showed that Mg²⁺ significantly stimulated IMET insensitive to rotenone–antimycin A–myxothiazol in mitochondria with the hypotonically damaged outer membrane, even in the absence of exogenous cytochrome c. This effect was more specific than simply ionic strength increase. Direct evidence for cytochrome c desorption from mitochondrial membranes under 4 mM Mg²⁺ influence was obtained to explain the stimulatory effect of Mg²⁺ on external NADH oxidation that was coupled to the inner membrane potential generation. Obtained data suggest that cytochrome b ₅ is normally oriented towards the cytosol in the outer membrane, and can be accessible for endogenous cytochrome c reduction only through the outer membrane rupture or permeabilization, to activate external NADH oxidation.

[学科分类] 生物化学/生物物理

[关键词] Liver mitochondrion;Exogenous NADH;Cytochrome c;Apoptosis;IMET;the intermembrane electron transport;MSHG;the medium composed of 210 mM mannitol;70 mM sucrose;0.02 mM EGTA;5 mM HEPES/Trizma;pH 7.4;HG;the medium composed of 5 mM HEPES/Trizma;0.02 mM EGTA;pH 7.4;RAM;rotenone–antimycin A–myxothiazol