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V. N. TARUSOV 



for survival. In higher animals this effect is masked due to the toxic 

 effect. Nevertheless, Zhuravlev (1959) in our laboratory has shown on 

 much material that irradiation of mice does not increase the toxic effect 

 of oxygen at pressures close to one atmosphere, and a slight increase 

 of the ability to survive has been noted. The curve in this case may be 

 regarded as a sum total of the toxic and the protective effects (Fig. 3). 



0-6 1-0 1-4 



Oxygen tension (P atm) 



Fig. 3. 



The protection of yeast at high oxygen pressures reveals the nature 

 of at least one of the primary reactions. If protection at low oxygen 

 pressure can be explained by the decrease in the products of water 

 radiolysis (if we ignore the peculiar features of the kinetics of the pro- 

 cess) it is difficult to connect with it protection at increased pressure. 

 With an increase of oxygen jiressure the amount of the products of 

 water radiolysis, especially of oxidizing products, must increase to a 

 threshold saturation at high pressures. 



On the basis of kinetic data we should suppose that the kinetic 

 tlu'eshold of oxygen protection is determined by an inhibition of the 

 oxidizing reaction developing in the organic lipid structural phases of 

 cells (Zhuravlev. 1959). 



Experiments with various biogenic components show that this type 

 of reaction could hardly arise on a different substrate. In that connec- 

 tion we have undertaken a wide investigation of protective action in 

 two lines of yeast, haploid and diploid, at high oxygen pressures. These 

 two lines greatly differ in radiosensitivity, 3,000 r for haploid LD50 and 

 40,000 r for diploid LD50. 



It has been established that both these lines behave differently at 



