Formation and disappearance of an endogenous uncoupling factor during swelling and contraction of mitochondria

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.

THE UNCOUPLING OF OXIDATIVE PHOSPHORYLATION BY IONIZING RADIATION

Whole body irradiation of rabbits or rats with X-rays or Co60γ-rays causes uncoupling of oxidative phosphorylation in thymus mitochondria, which is not prevented by the prior administration of AET. Whole body irradiation was not found to affect oxidative phosphorylation in liver or mouse ascites cell mitochondria. The radiation lesion can be repaired in vitro by the addition of cytochrome c, bovine serum albumin, or vitamin K1to mitochondria. Vitamin E and coenzyme Q10 were without effect. Both phosphorylating steps in the electron transport chain associated with succinate oxidation are affected by irradiation. The diphosphopyridine nucleotide dependent steps in the oxidation of α-ketoglutarate by thymus mitochondria are damaged by in vivo irradiation. Diphosphopyridine nucleotide levels of thymus and spleen but not liver or ascites cells are reduced by in vivo irradiation. No effect of in vitro irradiation on oxidative phosphorylation could be found for thymocyte cell suspensions, isolated thymus or liver mitochondria, or ascites or HeLa cell suspensions. Respiration of ascites or thymocyte cells was unaffected by in vitro irradiation.

THE UNCOUPLING OF OXIDATIVE PHOSPHORYLATION BY IONIZING RADIATION

Whole body irradiation of rabbits or rats with X-rays or Co60γ-rays causes uncoupling of oxidative phosphorylation in thymus mitochondria, which is not prevented by the prior administration of AET. Whole body irradiation was not found to affect oxidative phosphorylation in liver or mouse ascites cell mitochondria. The radiation lesion can be repaired in vitro by the addition of cytochrome c, bovine serum albumin, or vitamin K1to mitochondria. Vitamin E and coenzyme Q10 were without effect. Both phosphorylating steps in the electron transport chain associated with succinate oxidation are affected by irradiation. The diphosphopyridine nucleotide dependent steps in the oxidation of α-ketoglutarate by thymus mitochondria are damaged by in vivo irradiation. Diphosphopyridine nucleotide levels of thymus and spleen but not liver or ascites cells are reduced by in vivo irradiation. No effect of in vitro irradiation on oxidative phosphorylation could be found for thymocyte cell suspensions, isolated thymus or liver mitochondria, or ascites or HeLa cell suspensions. Respiration of ascites or thymocyte cells was unaffected by in vitro irradiation.