PROTEINS AND NUCLEIC ACIDS IN SOLUTION 



55 



the thin separating RNA layer (Fig. 3, curve 1). The second half of the 

 enzyme suspension in acetate buffer was exposed to X-irradiaton with 

 various doses; thereafter the substrate was added to this half of the 

 suspension and the rate of enzymic oxidation of ascorbic acid through 

 the RNA layer damaged by radiation was determined in the same way 

 (Fig. 3, curve 2). In the second case the oxidation of ascorbic acid 

 always proceeded faster. The activity of pure aqueous solutions of 

 peroxidase changed but little with the doses of irradiation used, 

 (28,000 to 70,000 r); besides, inactivation of the enzyme could only 

 lead to the slowing down of the rate of ascorbic acid oxidation but not 

 to an increase in this rate. In control protein RNA suspensions, where 

 the enzyme preparation was rej^laced by human serum albumin or on 

 mixing RNA and ascorbic acid solutions, radiation did not alter the 

 course of spontaneous ascorbic acid oxidation (Fig. 4), very much unlike 





50 



t (mm) 

 Fig. 4 



100 



the course of the curves in Fig. 3. Therefore, it seems that the accelera- 

 tion of the enzymic oxidation of ascoi'bic acid in irradiated peroxidase- 

 RNA suspension could be regarded as a result of an increased perme- 

 ability of the damaged thin RNA layer separating the enzyme and the 

 substrate, and of an acceleration of the diffusion stage of enzymic 

 reaction. Applying as the measure of acceleration of enzymic reaction 

 the ratio of the areas of curves 2 and I in Fig. 3 (and in similar experi- 

 ments with other doses) one can plot a further curve (Fig. 5) characteriz- 

 ing the dependence of the effect observed on the dose of radiation. 

 The dotted part of the curve in Fig. 5. corresponds to scattering of 

 points (about 7 per cent) in the control, in various unirradiated enzyme 

 suspensions. Thus, the dose of about 18,000 r can be seen to be the thres- 

 hold of the experimentally observable effect. It may seem that this 

 threshold lies above the doses of biological importance; it should be 

 taken into consideration, however, that in the suspensions tested the 



