54 Antoinette Pirie 



Perhaps enzymes are stable once formed, or perhaps they 

 wear out in use. Miller (1950) finds that depletion of protein 

 in the diet leads to loss of liver enzymes and replacement of 

 protein leads to their rapid restoration. Enzyme synthesis is 

 therefore possible in the non-dividing mammalian cell and 

 presumably takes place. In a number of experiments the 

 manifestation of radiation damage has depended on meta- 

 bolic activity and this could be imagined to be related to 

 wearing out and non-replacement of enzymes. In bacteria, 

 adaptive enzyme formation is not affected by doses that 

 prevent division but one wonders whether one can equate 

 bacteria that are extremely radioresistant with mammalian 

 cells that are radiosensitive. But at present we have no 

 evidence for failure of enzyme synthesis or failure of a key 

 enzyme after radiation of a mammalian cell. 



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