THE EFFECTS OF IONIZING RADIATIONS 

 ON ENZYMES IN VITRO 



W. M. Dale 



Department of Biochemistry, Christie Hospital and Holt Radium, Institute, 



Manchester 



One important task for the biologist is to correlate the 

 radiation effects obtained in experiments in vitro with those 

 in living matter. Since enzymes are essential constituents of 

 cells, this short survey of radiation effects on enzymes in vitro 

 is meant to form a background against which the action of 

 radiation in vivo should be viewed, and I hope that the follow- 

 ing papers and their discussion will open new ways of approach 

 to decide what part enzymes may play in the mode of action 

 of radiation in living matter. As you will presently see, we 

 shall have to consider not only radiation effects on enzymes 

 themselves but also radiation effects on non-enzymic sub- 

 stances in their relation to enzymes. 



Although enzymes are not, in their response to radiation, 

 fundamentally different from other substances capable of 

 reacting with radicals, their inactivation may have more far- 

 reaching biological consequences because of their catalytic 

 properties and the fact that they are present in cells in only 

 small amounts. It has been shown that they are subject to the 

 indirect action of radiation in aqueous solution (Dale, 1940), 

 i.e. via radicals, as well as to direct action in the dry state 

 (Lea, et al., 1944). 



When solutions of a crystalline enzyme are irradiated the 

 number of molecules inactivated to a given proportion of re- 

 maining activity by a given dose is constant and independent 

 of the initial concentration. In consequence the percentage 

 destruction in a dilute solution is greater than in a concen- 

 trated solution, and therefore a dilute solution would appear to 

 be radiosensitive and a concentrated one radioresistant. Thus 



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