Abstract
Cytochrome c is a member of the respiratory chain of the mitochondria. Non-membrane-bound (free) cytochrome c can be reduced by gluthatione as well as ascorbic acid. We investigated the effect of pH, Ca2+, Mg2+ and anionic phospholipids on the reduction of cytochrome c by glutathione.The reduction of cytochrome c by thiols was measured using photometry. Mitochondrial oxygen consumption was detected by use of oxygen electrode. Glutathione does not reduce cytochrome c at pH = 7.0 in the absence of Ca2+ and Mg2+. The reduction of cytochrome c by glutathione is inhibited by anionic lipids, especially cardiolipin. The typical conditions of apoptosis—elevated pH, Ca2+ level and Mg2+—increases the reduction of cytochrome c. Glutathione (5 mM) causes increased mitochondrial O2 consumption at pH = 8.0, in the presence of ADP either 1 mM Mg2+ or 1 mM Ca2+. Our results suggest that membrane bound cyt c does not oxidize glutathione. Free (not membrane bound) cytochrome c can oxidize glutathione. In mitochondria, O2 is depleted only in the presence of ADP, so the O2 depletion observed in the presence of glutathione can be related to the respiratory chain. Decreased glutathione levels play a role in apoptosis. Therefore, membrane unbound cyt c can contribute to apoptosis by oxidation of glutathione.
Highlights
IntroductionThe primary function of mitochondria is ATP production by the respiratory chain
In healthy cells, the primary function of mitochondria is ATP production by the respiratory chain
We tested whether glutathione could increase mitochondrial O2 intake, so could glutathione act as a respiratory substrate?
Summary
The primary function of mitochondria is ATP production by the respiratory chain. Cytochrome c (cyt c) is a member of the respiratory chain proteins, and it is located between complex III and complex IV in the intermembrane space of the mitochondrion. Electrons go to complex III from NADH or from succinate and fatty acids. The primary function of cyt c is electron shuttling in the oxidative phosphorylation process. In physiological conditions cyt c is bound to the inner mitochondrial membrane. At physiologic pH, cyt c is a positively charged protein; it mainly binds to anionic lipids such as phosphatidyl-serine or mitochondric-specific cardiolipin through electrostatic and hydrophobic interactions
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