86 D. W. VAN Bekkum 



between the control and the irradiated groups. Similar results 

 have been obtained with this technique in thymus glands. 



An increase of ATPase activity in spleen homogenates 

 after total body irradiation has been reported by several 

 authors (Ashwell and Hickman, 1952; Dubois and Petersen, 

 1954) and the question arose whether the depression of oxida- 

 tive phosphorylation might be related or even secondary to 

 this phenomenon. A more detailed investigation showed that 

 the increase of ATPase activity appears several hours after 

 the disturbance of oxidative phosphorylation has become 

 established. Furthermore, normal ATPase activities were 

 found in mitochondria that exhibited a markedly decreased 

 phosphorylating capacity (van Bekkum, 1955b). Finally 

 Petersen, Fish and Dubois (1955) reported that the ATPase 

 effect is absent after irradiation of the exteriorized spleen 

 exclusively and it should therefore be classified among the 

 secondary radiation effects. 



The decrease in anaerobic glycolysis which was described 

 by Hickman and Ashwell (1953) in mouse spleen homogenates 

 one or more days after a total body irradiation, was found to 

 be absent at 2 and 4 hours after irradiation, when oxidative 

 phosphorylation was severely depressed (van Bekkum, 1955a). 

 It was concluded that different mechanisms are probably 

 involved in the development of these biochemical changes. 



At present we are engaged in an investigation of the various 

 phosphorylative steps in spleen mitochondria from irradiated 

 rats. So far, some interesting data have been obtained on 

 the relation of cytochrome c to the depression of oxidative 

 phosphorylation. When cytochrome c is omitted from the 

 succinate reaction system both phosphate uptake and oxygen 

 consumption drop about 50 per cent in the control prepara- 

 tions. In other words the addition of cytochrome c causes an 

 appreciable stimulation (cytochrome c effect). This cyto- 

 chrome c effect is found to be consistently increased after 

 irradiation (Table III). 



Even at 30 minutes after irradiation (700 r) a slightly 

 increased cytochrome c effect has been observed. If the 



