UNCOUPLING OF OXIDATIVE PHOSPHORYLATION BY IONIZING RADIATION: II. THE STABILITY OF MITOCHONDRIAL LIPIDS AND CYTOCHROMEc

Mitochondria isolated from the thymus of rats or rabbits 4 hours after 800 rads of ionizing radiation show uncoupling of their oxidative phosphorylation. There are no significant differences in the contents of phospholipids, neutral lipids, or total fatty acids between normal and uncoupled mitochondria. There was no evidence of the formation of any lipid uncoupling factor in thymus mitochondria from irradiated animals.Heart or liver mitochondria isolated from animals irradiated up to 12 hours previously showed no uncoupling of oxidative phosphorylation although preparations in various media could be made with reduced cytochrome c contents. No effect of irradiation upon endogenous cytochrome c or its binding in these mitochondria could be detected.Thymus mitochondria would appear to contain very low quantities of cytochrome c (less than 0.2 μg per mg protein), yet still be tightly coupled. It is suggested that this low level may indicate a critical condition at which radiation damage could become manifest.