EFFECT OF X RAYS ON BIOLOGICAL SYSTEMS 



293 



changes in the absorption spectrum increase with the irradiation dose up 

 to the point when protein denaturation appears, and are more marked in 

 dilute solutions (0.04 per cent egg albumin) (Fig. 5-2). The dose 

 recjuired to reach a given per cent of increase in absorption is proportional 

 to the protein concentration, and the absolute rate of reaction appears to 

 be independent of the protein concentration (Buchanan and Barron, 

 1947). In agreement with the results of Sanigar et al. (1939), a 0.4 per 



240 250 260 270 280 290 300 310 

 WAVE LENGTH, mju 

 Fig. 5-2. Effect of X rays on absorption spectrum of egg albumin. Egg albumin 

 1 X 10^5 M dissolved in water. Curve 1, control. Curve 2, radiation dose of 

 4300 r. Curve 3, radiation dose of 19,260 r. Curve 4, radiation dose of 32,250 r. 



cent solution of egg albumin shows no significant change after irradiation 

 with 19,000 r. Changes in the absorption spectrum at 2800 A depend on 

 the pH of the solution, being minimum at pH 3 and maximum when the 

 protein is irradiated in alkahne solutions. This is due to the dissociation 

 degree of the hydroxyl group of tyrosine (Barron and Gasvoda, 1949a). 

 Early investigators believed that the effects produced by ionizing radia- 

 tions were similar to those produced by heat, acid, and base denaturation 

 and by H2O2. The changes observed in the absorption spectrum of 

 protein resulting from the action of ionizing radiations are different from 

 those observed on irradiation with ultraviolet light, on denaturation by 

 heat or acid, or on addition of base. H2O2 added at a concentration which 

 would be produced by irradiation of water with 250,000 r (5 X 10~^ M) 

 has no effect on the absorption spectrum. If to this solution (albumin + 

 H2O2) FeS04 is added (5 X 10~^ M) in order to produce hydroxyl radicals 



