Air saturation of the medium reduces the rate of phosphorylating oxidation of succinate in isolated mitochondria

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Abstract
Rat brain mitochondria were isolated and their respiration was polarographically measured without contact with air oxygen. Gas‐saturated experimental mixtures close to the in vivo partial oxygen pressure (normoxic) were compared with the air‐saturated, i.e. hyperoxic, mixtures. The rate of phosphorylating oxidation of added succinate under normoxic conditions was found to be 70–100% higher compared with hyperoxic ones. The addition of succinate dehydrogenase activators results in a more than two‐fold stronger stimulation of succinate oxidation under normoxia than under hyperoxia. Thiol group donors are shown to stimulate respiration under hyperoxia and not under normoxia. Hyperoxic conditions prevented oxidation of the low succinate concentrations corresponding to the physiological ones.