ACCELERATED HEAVY IONS ON ENZYMES AND YEASTS 



261 



(1960) and Braams et al. (1958) found variations of radiosensitivity of 

 dry enzymes \\'hen mixed with some inert materials. Figure 2 presents 

 data showing that dextran and ribose increase the cross-section of 

 trypsin, whereas pinacyanole protects and cysteine leaves the cross - 

 section unaltered. It is of interest to note that the protection increases 

 as the concentration of the modifier is increased and that a total of 

 four-fold variation in a has been achieved. The protection afforded by 

 lactose is shown in Fig. 3, and we may note that cysteine can reverse 



c 

 O 



1) 







20 40 60 



mg Lactose/mg Trypsin 



Fig. 3. — Increase of cross-section of dry trypsin by the addition of lactose. 



lactose protection. In looking at the quantitative aspect of protection 

 we may note that pinacyanole and dextran, both small molecules 

 already exert an effect at concentrations where there are insufficient 

 modifier molecules present to cover the entire surface of the trypsin 

 molecules. On the other hand in lactose and ribose enhancement of the 

 radiation effect the cross-section is still increasing after the modifier 

 molecules have covered the entire surface of the trypsin molecules. It 

 would thus appear that in some instances an increase of cross-section is 

 caused by modifier molecules which are as far as 30 A away from the 

 enzyme molecules affected. Interpretations are made more difficult by 

 the circumstance that the enzyme molecules are always dissolved in an 

 aqueous system for assay and one does not know at which stage of the 

 process a protective or enhancing effect occurs. We have also observed 

 an effect of temperature on inactivation cross-sections, as did Hutchin- 

 son (1960). Further the pH of the solution from which the enzyme is 

 dried has an effect. Results such as these make it particularly difficult 

 to estimate how much of the radiation effects on enzymes in living cells 



