30 



THE IN VITRO EFFECTS OF RADIATIONS ON 

 MOLECULES OF BIOLOGICAL IMPORTANCE 



E.S.G. Barron 



We have heard Dr. Pollard's very thorough discussion about the action 

 of ionizing radiations on "dry" matter. I am now going to speak on the action of 

 ionizing radiations on aqueous solutions and the role of oxygen. As Dr. Pollard 

 has already stated, the living cell contains about 80 percent water. Moreover, 

 in most cases, it is oxygen-saturated water. The biologist is therefore mainly 

 interested in the action of ionizing radiations upon oxygen-saturated aqueous so- 

 lutions. 



I have been asked to talk about the action of ionizing radiations upon 

 substances of biological importance and to attempt to draw from these studies 

 conclusions that are of interest to the cell physiologist. I will start with the ox- 

 idation-reduction reactions that are brought about by ionizing radiations. In oxygen- 

 ated aqueous solutions, we have the formation of three powerful oxidizing agents: 

 the radicals OH, O2H, and H^O^. Atomic hydrogen seems to recombine quick- 

 ly to form the unreactive molecular hydrogen. The only reduction reactions, 

 reported to be caused by irradiation, have been reductions of inorganic com- 

 pounds, such as eerie sulfate in acid solutions, and permanganate, bromate, 

 chromate, iodate, systems with an Eo above +0,9 v, which are of no biological 

 interest. Substances of biological importance, such as the respiratory pigments, 

 ascorbic acid, glutathione, lactic acid, ethanol, dihydrodiphosphopyridine nu- 

 cleotide (DPNH), coenzyme A, and formic acid are all oxidized, whereas the ox- 

 idized states are not reduced at all (1). 



The hydrogen atoms, which are presumably formed by irradiation of 

 water, show little activity. Probably the rate of recombination to molecular hy- 

 drogen is too fast. For example, ferricytochrome £, which is easily reduced by 

 black platinum and hydrogen, is not reduced by X irradiation up to 100, 000 r, 

 the maximum exposure that can be used without producing protein denaturation 

 (2). The same thing occurs with glutathione. Whereas reduced glutathione is 

 oxidized by irradiation, oxidized glutathione is not reduced (3). 



KAMEN: Did you see any hydrogen produced? 



BARRON: We did not measure hydrogen production. What we say is 

 that it has been impossible for us to produce reduction reactions by irradiating 

 aqueous solutions of substances of biological importance. 



