PROTEINS AND NUCLEIC ACIDS IN SOLUTION 



47 



cent solution) could be revealed after as small an irradiation dose as 

 400 to 500 r. 



The isoto])ic procedure was also a|)])lied to the detection of changes 

 in serum albumin and serum globulin after y-irradiation or after mixed 

 neutron irradiation in a nuclear reactor, as well as to the X-irradiation 

 of lipoproteins isolated from horse serum (Volkova and Passynsky, 

 1955). The data obtained are given hi Table I. 



Table I. Thresholds of detect able radiation action 



Substances 



Irradiation 



Thresholds in thousands of r 

 by trivial phys.-chem. by isotopio method 

 methods (viscosity, elec- 

 trophoresis, etc.) 



Human serum albumin 



Lipoproteins 



(from horse serum) 

 Nucleoproteins 



(from the thymus) 



j^-rays 



y-rays 



Neutrons 



X-rays 



75 to 100 

 100 

 250 



1,000 



005 



0-4 to 0-5 

 5 

 5 



50 



Thus, the threshold of the action observed could be lowered 20-fold 

 for lipoproteins and up to 200-fold for proteins. 



When irradiating a high molecular weight nucleoprotein isolated 

 from the thymus (N/P 3-3; 0-2 per cent solution in 1 M NaCl), no iso- 

 topic measurements were taken, since an appreciable radiation action 

 was observed with as small a dose as 25 to 50 r by the decrease of the 

 relative viscosity (Table I). At this dose the decrease of the relative 

 viscosity was 4-5 per cent, while after 500 r it was 20 per cent (Volkova 

 and Passynsky, 1955). 



Thus, by means of sufficiently sensitive methods, the presence of 

 definite molecular changes in the main classes of biological polymers 

 can be revealed even with sublethal doses, with 400 to 500 r for proteins 

 and 25 to 50 r for nucleoproteins. This result thus deprives the nucleic 

 acids and nucleoproteins of the peculiar position ascribed to them by 

 various theories of the biological action of radiations where these sub- 

 stances appeared to be the sole well-founded target for the action of 

 sublethal doses of radiation, while other substances appeared either as 

 inert media or as objects of secondary changes in the organism. On the 

 conti-ary, protein molecules undergo change after these small doses, and 

 it is evident that primary changes in cellular materials must be of a 

 sufficiently general and wide-spread character. Hundreds and thousands 



