42 Antoinette Pirie 



1953). Cytochrome c itself is not affected in Tlsch. coli (Hagen, 

 1955), nor is the uptake of radioactive ^^Fe into cytochrome b 

 of the liver (Bonnichsen and Hevesy, 1955). 



The citric acid cycle accounts for a large part of the oxida- 

 tive metabolism of the tissues. The activity of the enzymes 

 of this system can be determined by determining the formation 

 of fluorocitric acid after injection of fluoroacetate. DuBois, 

 Cochran and DouU (1951) have found that a lethal dose of 

 X-rays to the rat inhibits fluorocitric acid accumulation in the 

 spleen, thymus and kidney within three hours. A dose of 100 r 

 inhibits synthesis temporarily in the spleen only. Now within 

 three hours these tissues will be already grossly altered struc- 

 turally and hence one cannot conclude that radiation has had 

 a direct or indirect effect on the enzymes concerned. That it is 

 a secondary effect is suggested by the fact that if the spleen 

 is exteriorized and it alone is irradiated (Table I) the fall in 

 citric acid synthesis does not occur (Petersen, Fitch and 

 DuBois, 1955). 



Table I 

 Citrate Synthesis in Rat Spleen 



Next, to consider coenzymes. These substances are 

 ubiquitous and function in many different metabolic processes 

 so that change in activity could have wide effects. Diphospho- 

 pyridine nucleotide coenzymes are thought to be synthesized 

 in the nucleus and change might indicate change of nuclear 

 function. No immediate change in their activity has, however, 

 been found. Eichel and Spirtes (1955) found no change in 

 the oxidized or reduced DPN content of rat liver 1 • 5 min. 

 after a lethal dose to the whole animal. Coenzyme A activity, 

 measured as the power of the animal to acetylate sulphanil- 



