Oxidative Phosphorylation in Irradiated Cells 79 



include detailed results. Maxwell and Ashwell (1953) have 

 reported a decrease in oxidative phosphorylation of mouse 

 spleen mitochondria at 1-7 days after a lethal dose of total 

 body irradiation. The cellular composition of the spleen has 

 undergone radical changes at the time of their studies, so 

 that the results do not throw much light on the significance of 

 the disturbance with regard to the initial radiation effect. 



Most of our own observations have been made 4 hours or 

 less after irradiation and considerable attention has been paid 

 to simultaneously occurring cytological effects. Part of the 

 results, which have already been published, will be reviewed 

 briefly below. 



Methods 



To enable the reader to evaluate our data, a few remarks 

 on the methods employed will be made. The animals — rats in 

 most of the experiments — were irradiated with penetrating 

 X-rays (H.V.L. : 1-8 mm. Cu, dose rate 45 r/min.) under 

 conditions of maximum backscatter. The mitochondria were 

 isolated by differential centrifugation of the homogenates in 

 0-25 M sucrose solution. Generally the mitochondria were 

 washed twice. The preparations thus obtained from spleen 

 and thymus contain a certain amount of impurities, part of 

 which consists of small nuclear fragments. With the various 

 homogenating techniques it has not been possible to disrupt 

 the majority of the cell membranes without simultaneously 

 breaking a significant number of nuclei. In view of the fact 

 that most of the cells of these tissues have only a narrow 

 brim of cytoplasm surrounding a large nucleus, this may 

 be expected. Oxidative phosphorylation has been measured 

 in a medium containing succinate or a-ketoglutarate as a 

 substrate. Adenylic acid was added to provide phosphate 

 acceptors, and hexokinase plus glucose were employed as a 

 trap for the terminal phosphate group of ATP. MgClg, 

 fluoride, ethylenediamine tetracetate and cytochrome c were 

 present in the system. DPN was added when a-ketoglutarate 



