Electron Transport and Oxidative Phosphorylation in Arum Spadix Mitochondria |
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Authors: | PASSAM, H. C. PALMER, J. M. |
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Abstract: | Arum spadix mitochondria exhibited a rapid cyanide-resistantoxygen uptake when oxidizing malate, NADH2 or succinate, anda slower, cyanide-sensitive oxygen uptake when oxidizing ascorbate+tetramethylphenylenediamine(TMPD). Cytochrome oxidase does not therefore appear to functionas the terminal oxidase in the presence of cyanide, and therather low cytochrome c oxidase activity obtained using ascorbate+TMPDmay exclude it from possessing a major role even in the absenceof cyanide. ATP synthesis has been shown to accompany substrateoxidation. In the presence of antimycin A the P: O ratio accompanyingmalate oxidation was reduced by half, while phosphorylationaccompanying NADH2 or succinate oxidation was almost completelyabolished. It is proposed that electrons from exogenous NADH2enter the electron transport chain at a site after that whereendogenous NADH2 donates electrons and that electrons from exogenousNADH2 are not coupled to ATP synthesis at site 1. The cyanide-resistant,non-phosphorylating electron-transport pathway may functionin the absence of cyanide and account for the low efficiencyof energy conservation observed in this tissue. |
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