EFFECT OF X RAYS ON BIOLOGICAL SYSTEMS 



299 



small amounts of catalase previous to irradiation. Whatever part H2O2 

 has taken in the inhibition will be abolished by catalase (catalase is resist- 

 ant to irradiation). Complete protection of the enzymes is obtained on 

 addition of glutathione. The effect of ionizing radiations on a number 

 of other enzymes has been studied. In general, increasing the dose of 

 radiation will bring about inhibition of very dilute solutions. Trypsin 

 (Hussey and Thompson, 1922-23; Barron, Dickman, Muntz, and Singer, 

 1949); pepsin (Northrop, 1934); ribonuclease (Lea et al., 1944; Barron, 

 Dickman, Muntz, and Singer, 1949) ; catalase (Forssberg, 1947) ; urease 

 (Tytell and Kersten, 1941 ; Barron and Dickman, 1949) ; carboxypeptidase 

 (Dale, 1940); D-amino acid oxidase (Dale, 1942); papain (Feigenbaum, 

 1950) ; desoxyribonucleic acid depolymerase (Manoilov and Semenov, 

 1950) ; and serum phosphatase (Albers, 1940), are inhibited by irradiation. 

 The ionic yield of some of these enzymes is given in Table 5-4. 



Table 5-4. Ionic Yield of Enzymes Inhibited by X Rays 

 Enzyme Ionic yield 



Alcohol dehydrogenase 1 . 05 



Phosphoglyceraldehyde dehydrogenase . 93 



Trypsin 0.025 



Ribonuclease . 03 



Carboxypeptidase 0.16 



D- Amino acid oxidase 0.1 



Catalase 0.0027 



There is little information on the relative efficiency of different radia- 

 tions toward enzyme systems. In reactions in the gaseous state the 

 ionic yields with different ionizing radiations are in general similar. In 

 the production of H2O2 on irradiation of water saturated with oxygen, 

 Frilley (1947) reported similar ionic yields for X-ray and for a-ray irra- 

 diation. On irradiating carboxypeptidase with a and mth X rays, Dale, 

 Gray, and Meredith (1949) found the efficiency of a rays only 5 to 9 per 

 cent of that of X rays. In irradiation of the sulfhydryl enzyme phos- 

 phoglyceraldehyde dehydrogenase, the efficiency of a, ^, and X rays is 

 about the same, while in irradiation with 7 rays the ionic yield is some- 

 what lower (Barron and Dickman, 1949) (Table 5-5). The equal effi- 



Table 5-5. Ionic Yields of Enzyme Inhibition by X, a, /3, and 7 Rays 



Enzyme 



Phosphoglyceraldehyde dehydrogenase 

 Phosphoglyceraldehyde dehydrogenase 

 Phosphoglyceraldehyde dehydrogenase 

 Phosphoglyceraldehyde dehydrogenase 



Carboxypeptidase 



Carboxypeptidase 



Ionizing 

 radiation 



X rays 

 a rays 

 (3 rays 

 7 rays 

 X rays 

 a rays 



Ionic yield 



0.93 



1.0 



1.2 



0.7 



0.16 



0.01 



