88 D. W. VAN Bekkum 



of cytochrome c being aggravated as a result of irradiation, 

 the cytochrome c effect was estimated at 2 hours after 

 irradiation in unwashed mitochondria. A comparison of the 

 results (Table IV) wdth those obtained on twice washed 



Table IV 



Effect of the Addition of Cytochrome c and of DPN on Oxidative 



Phosphorylation of Unwashed Spleen Mitochondria from Control 



and Irradiated Rats (2 Hours after 700 r)* 



Phosphate uptake Og uptake 



control irradiated control irradiated 



119 360 102 195 



% stimulationt by cyto- 

 chrome c in succinate 

 system 



% stimulationt by DPN 

 in a-ketoglutarate 

 system 8 5 7 13 



• Values represent means of 3 experiments; 4 control and 4 irradiated rats were used per 



t Stimulation is expressed in percentage of the values obtained in the absence of the stimulat- 

 ing substance. Concentrationof cytochrome c: 2-8 x 10-*m; DPN: 4 x 10-*M. 



mitochondria (Table III) shows that the cytochrome c effect is 

 not increased by washing. Therefore this simple explanation 

 cannot be applied. It is also to be noted that irradiation does 

 not result in an increased leakage of DPN. 



Conclusions 



At present we are still far from a complete understanding 

 of the biochemical changes that take place in spleen mito- 

 chondria after irradiation. However, it seems fairly certain 

 that these changes occur shortly after irradiation and that the 

 cytochrome system is somehow involved. It is tempting to 

 connect the fact that irradiation affects this part of the respi- 

 ratory chain with the well-known observations on the oxygen 

 effect in irradiation experiments with living organisms. 



In this connection it is of interest that Laser (1954) has 

 also suggested the involvement of the cytochromes in the 

 biochemical effect of radiation. However, much additional 

 information is required before the nature of this involvement 

 can be more accurately defined. 



