THE EFFECT OF LETHAL DOSES OF X-IRRADIATION ON THE ENZYMATIC ACTIVITY OF MITOCHONDRIAL CYTOCHROME c
The coupling of the tetrazolium salts triphenyltetrazolium chloride and nitro-blue tetrazolium to the electron transport chain in mitochondria of thymus, spleen, liver, kidney, and Ehrlich ascites carcinoma cells has been studied with several substrates. In experiments on succinate–triphenyltetrazolium chloride reductase activity it has been possible to demonstrate a radiation lesion in the electron transport chain of mitochondria from thymus and spleen, but not in those from other tissues. This lesion is evident 4 hours after 25 rad of whole-body irradiation, or earlier with higher doses. It is not prevented by the prior administration of aminoethylisothiouronium bromide, serotonin, vitamin K1, or vitamin E, but is reduced by anoxic conditions.Lower levels of cytochrome c are found in irradiated mitochondria isolated from thymus, and the radiation lesion is believed to be produced by loosening the binding of cytochrome c to the mitochondrial membrane after X-irradiation. Decreased levels of ATP occur in thymus, spleen, and ascites cells following irradiation.