Oxidative Phosphorylation in Irradiated Cells 81 



were used as substrate (Table I). In the experiments with 

 succinate the oxygen uptake was depressed to a less extent 

 than the phosphate uptake, which resulted in a decreased 



Table I 



Oxidative Phosphorylation of Rat Spleen IMitochondria 4 Hours 



AFTER Irradiation (1100 r.)* 



Phosphate O^ uptake PjO ratio 



uptake [latomslmg.N 



\imolelmg.N 



Substrate: succinate 0-01 m 



controls (18) 32-7±70 28-9±3-8 114+019 



irradiated (19) 171+50 22-8±4-8 0-82±0-23 



P of difference <0001 <0 001 <0 001 



Substrate: cc-ketoglutarate 01 m 



controls (7) 34-9±6-8 19-7±4-0 l-82±0-44 



irradiated (6) 20-9±7-4 130±2-2 1-61 ±0-36 



P of difference <001 <001 <0-2 



* Figures represent means ± s.D. Figures between brackets indicate number of experiments. 



P/0 ratio. With a-ketoglutarate the decrease in oxygen 

 uptake was more pronounced, and the decrease in the P/0 

 ratio was not statistically significant in this relatively small 

 series of observations (van Bekkum et al., 1954). 



Effect of radiation dose 



It was soon realized that the above experiments had been 

 performed on a tissue which contained large numbers of dead 

 and degenerating cells. Therefore the effect of the radiation 

 dose on the disturbance of the oxidative phosphorylation, as 

 well as on the amount of nuclear degeneration, was studied. 

 The interval between radiation and the kiUing of the rats was 

 kept at 4 hours. Doses down to 300 r were found to cause a 

 marked decrease in the phosphate uptake of both spleen and 

 thymus mitochondria. The minimal effective dose appeared 

 to be about 100 r in spleen and 50 r in the case of thymus mito- 

 chondria. The histological sections of these thymus glands, 

 after dosage with 50 r, showed definite changes at 4 hours. 



