Observations on the oxidoreduction of the two cytochromes b in cytochrome c-deficient mitochondria and submitochondrial particles.
1. In cytochrome c depleted mitochondria cytochrome bT is reduced rapidly upon addition of ATP or slowly during state 4 respiration, but cytochrome bK is effectively reduced in such mitochondira respiring upon glutamate plus malate in all energy states. In mitochondria or in submitochondrial particles oxidized NADH or succinate, cytochromes bK and bT were always reduced and oxidized independently. 2. Difference spectra for the two b cytochromes were obtained in the presence of respiratory chain inhibitors. Reduced cytochrome bK in the presence of cyanide can be reoxidized by CoQ2. Cytochrome bT reduced in the presence of antimycin can be reoxidized by O2 if rotenone is added to an NADH-reduced sysem or malonate to a succinate-reduced system. There is no evidence for electron transfer between the two b cytochromes. 3. It is suggested that there is no electron transfer from cytochrome bT to cytochrome bK, but that a cytochrome bKbT dimer accepts electrons from the CoQ pool jointly with cytochrome c1 and another acceptor, perhaps the FeS centre. The major steady state species is b2K+b3T+, and a Q-loop occurs with reduction of CoQ by the fully reduced species b2K+b2T+. All proposed interactions between CoQ and Complex III are 2-electron processes and the change from 2-electrons to 1-electron transfer occurs within Complex III itself.
D000968:Antimycin A / Q000494:pharmacology; D002474:Cell-Free System; D003486:Cyanides / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism*; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D010084:Oxidation-Reduction; D012402:Rotenone / Q000494:pharmacology; D013057:Spectrum Analysis; D014451:Ubiquinone / Q000494:pharmacology
D003486:Cyanides; D003574:Cytochrome c Group; D003580:Cytochromes; D012402:Rotenone; D014451:Ubiquinone; D000968:Antimycin A