Ionizing Radiations and Enzymes 



27 



The ionic yield of the esterase activity was three times greater 

 than that of protease activity. A possible explanation given 

 was that there are two active centres in the molecule. 



The initial ionic yields for various enzymes generally lie 

 between 1 and 0-1. An example of a very low yield is catalase 

 which is of the order of 10"^, though there is, according to 

 Forssberg (1946), some dose-rate dependence. A low ionic 



INDIRECT 



u 



< 

 o 



< 



cc: 



>IRECT| 

 I S 10 IS 



g. ENZYME PER lOOg. SOLUTION 



Fig. 2. Relative contribution of "Indirect" and 



"Direct" action to the total effect of X-rays on car- 



boxypeptidase in solution (Dale, 1947. Reproduced by 



permission of Brit. J. Radiol.). 



yield of this powerful enzyme may be of importance to its 

 survival and its consequent availability for decomposing 

 HgOo formed by radiation. 



Returning to Fig. 1, it will be seen that the constancy of the 

 yield extends to a concentration of 15 per cent, at which the 

 enzyme is no longer soluble. It will be useful to demonstrate 

 how much of the radiation effect has to be assigned to the 

 direct and to the indirect actions respectively, at the various 

 concentrations. 



Fig. 2 demonstrates the respective contributions to the 

 observed effect, at various concentrations, of both the direct 



