Enzymes in Irradiated Tissues 41 



radiation that prevents cell division. This does not lend 

 support to the view that the gradual decay of enzymes after 

 irradiation of animals is due to failure of synthesis, but the 

 evidence is far too scanty to be taken as refuting such a view. 



It seems useless to attempt to catalogue all the work that 

 has been done which shows delayed effects of radiation on cell 

 enzymes. This includes my own work on lens metabolism. 

 It would appear to be more profitable to make a few bald 

 statements which can be amphfied, if necessary, in discussion. 

 This may lead to oversimplification but a detailed presenta- 

 tion leads only to confusion. 



Within the boundaries of our ignorance it seems true to say 

 that lethal doses of radiation do not immediately change the 

 overall oxygen consumption of the animal or the major 

 respiratory enzymes. There is no change in oxygen consump- 

 tion of guinea pigs after an LD50 of X-rays (Smith, Budding- 

 ton and Greenan, 1952) or of the rat during the first four 

 days after a lethal dose (Mole, 1953). On the other hand, liver 

 dispersions examined 6 hours after whole body X-ray show 

 increased endogenous respiration (Kunkel and Phillips, 1952), 

 as do also bone marrow cells from the rabbit examined as 

 soon as possible after radiation (Altman, Richmond and 

 Solomon, 1951). These increases may indicate that there has 

 been a change in substrate concentration or another form of 

 enzymic activation. They are evidently insufficient to alter 

 the oxygen consumption of the whole animal. With Esch. coli, 

 Billen, Stapleton and Hollaender (1953) found that with one 

 strain a killing dose made no immediate difference to respira- 

 tion with glucose, succinate and pyruvate. With another 

 there was an immediate fall in oxygen uptake with pyruvate. 



Cytochrome oxidase and succinic dehydrogenase, two major 

 respiratory enzymes of the mitrochondria, have been widely 

 investigated and in no case has any change been found as a 

 result of radiation, even hours or days later (Powell and 

 Pollard, 1955; Ashwell and Hickman, 1952; LeMay, 1951; 

 Hagen, 1955; Ryser, Aebi and Zuppinger, 1954; Thomson, 

 Tourtellottc and Carttar, 1952; Fischer, Coulter and Costello, 



