PHOSPHORYLATING ACTIVITY OF 

 MITOCHONDRIA AFTER TOTAL BODY 



IRRADIATION 



D. VV. VAN Bekkum 



Medical Biological Laboratory of the National Defence Research Council, Rijswijk, 



Netherlands 



The interference with mitosis and the death of living cells after exposure 

 to ionizing radiation are commonly assumed to be the outcome of some 

 primary damage to the cell nucleus. Most morphological and biochemical 

 changes so far described after irradiation have been localized in the nucleus. 

 Pycnosis and karyorrhexis, structural damage to chromosomes and inhibition 

 of DNA synthesis are among the most widely recognized cellular effects of 

 irradiation. There are however reasons to question the assumption that 

 radiation damage is primarily to the nucleus (Trowell^ and Mole-). 



Therefore some years ago studies were initiated in this laboratory with the 

 object of collecting information on the effect of ionizing radiation on metabolic 

 processes in the cytoplasma. It was postulated that the interference with 

 nuclear function, e.g. cell division and DNA synthesis, which follows exposure 

 to irradiation, might well be the consequence of damage to biochemical 

 reaction systems outside the nucleus. Since synthetic processes in the nuclei 

 are generally supposed to be dependent on energy-generating reactions which 

 occur in the cytoplasma, the oxidative phosphorylation of mitochondria 

 seemed to present the most obvious subject for investigation. 



In preliminary experiments with mitochondrial preparations from various 

 tissues, it was found that spleen mitochondria showed a decreased phosphate 

 uptake shortly after total body irradiation. Most of our subsequent work 

 has been carried out with rat spleen tissue because of its radiosensitivity and 

 its relative abundance per animal. A decrease of oxidative phosphoryla- 

 tion of isolated spleen mitochondria following total body exposure to X-rays 

 has since been reported by several investigators. In 1952 Potter and 

 Bethel^ described a decrease of phosphate uptake by mitochondria, isolated 

 from rat spleen after total body irradiation with 800 r. Similar observations 

 were reported shortly afterwards by ourselves (van Bekkum et al^). In these 

 experiments also rather large doses of X-radiation, namely 800 r and l,100r, 

 were administered to rats and spleen mitochondria were isolated 2, 4 and 

 24 hours afterwards. In addition to a diminished phosphate uptake, some 

 decrease of oxygen consumption was observed in most experiments, although 

 the latter effect has been generally of lower magnitude. Thus a decrease 

 of P/O ratios has been consistently found with several substrates. 



Maxwell and Ashvvell-^ have published comparable results obtained 

 with mitochondrial preparations from mouse spleen at 1-7 days after a 

 lethal dose of total body X-irradiation. It should be pointed out that in 

 general the study of biochemical reactions in highly radio-sensitive tissues 



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