MAURICE ERRERA 



Respiration also responds in some instances to irradiation. The most 

 systematic studies were performed b)' Barron who showed a decrease in the 

 respiration of irradiated tissue sHces and grasshopper eggs. This effect was 

 attributed to the radio-oxidation of the — SH groups of succinic dehydro- 

 genase (Barron, Gasvoda and Flood ^".) Similar results were obtained 

 on liver respiration by Marsili and Paleotti^'. However Le May^- did not 

 find any inhibition of succinoxidase, succinic-dehydrogenase or cytochrome 

 oxidase, and Dubois also found no inhibition-^. In some cases, as reported 

 by BiLLEN, Stapleton and Hollaender, respiration of E. coli is even 

 increased after irradiation^*. 



An effect of the Krebs cycle seems nevertheless apparent after in vivo 

 irradiation of mice injected with radioactive glucose : there is a marked 

 decrease in the radioactive CO2 produced (Hevesy and Forssberg^^). 

 However all tissues do not respond similarly : C^^Og production is increased 

 immediately after irradiation in the bone marrow (Altman, Richmond and 

 Salomon^). Dubois and Kochran^" have, on the other hand, shown an 

 inhibition of citric acid synthesis in bone marrow. These results indicate 

 that, at least in some tissues, the large cytoplasmic granules (mitochondria) 

 have been affected ; this has also been shown cytochemically by Janus 

 green staining*'*. This is also supported by the numerous instances of inhibi- 

 tion of phosphorylation. Ashwell and Hickman^ showed that spleen 

 homogenates of irradiated animals synthesize less energy rich P bonds, 

 althouarh their succinoxidase is not affected. This inhibition increases 

 during the first 3 days after irradiation, but may in some instances be demon- 

 strated as early as one hour after irradiation (Potter and Bethell^"). 

 Van Bekkum obtained similar results in spleen'*, but in E. coli no inhibition 

 of phosphorylations seems to occur, although one does find a leakage of ATP 

 into the medium^* and Florsheim found no inhibition of phosphorylations 

 in mouse brain^". 



These inhibitions may be the result of the inactivation of a single enzyme 

 of the chain of reactions if it exists in limiting amounts and if no protecting 

 agent is available at the time of irradiation, as has already been pointed out 

 by BoELL^'\ Thus most of these complex systems may be, but are not 

 always (it may depend on the tissue or experimental conditions), inhibited by 

 irradiation. 



Very st-imulating experiments by Sherman^^' ^^ may throw some light on 

 these discrepancies. If yeasts are grown on a medium rich in nitrogen, 

 one finds no eflfects of X-rays on glycolysis ; but if these organisms are grown 

 on a synthetic medium poor in nitrogen, dosages of about 30. lO^r will be 

 inhibitory. This may mean that competitive constituents have been 

 eliminated by the low nitrogen diet and the enzymes of glycolysis become 

 more exposed. 



(5) Synthesis of lipids, proteins and nucleic acids 



As we have just seen, radiation eflfects on isolated proteins or on energy 



yielding systems do not appear to be of constant importance : in some cells 



the activity of these systems may even be increased after irradiation. It was 



therefore necessary to look for eflfects on systems of a greater complexity 



still. 



97 H 



