54 



CELLULAR BIOCHEMISTRY 



Frederick G. Sherinan 



The discussion yesterday was encouraging because it is becoming evi- 

 dent that it may be possible to construct some models of the interaction of radi- 

 ation with complex molecules that might be applicable to living systems. It is 

 encouraging, too, that radiobiologists are beginning miore and more to utilize 

 technics that can uncover some of the physiologicfal effects that take place rela- 

 tively soon after irradiation. Evidence for short-term effects of irradiation has 

 been obtained with a wide variety of organisms. The period I have in mind as 

 being covered by "short-term" ranges from a few minutes to not more than a 



few hours. 



20 60 100 140 



TIME( MINUTES) 



Figure 1. The respiratory activity of X- 

 irradiated Escherichia coli, Strain B/r, 

 on several substrates. The control cups 

 contained 20 x 108 and the experimentals, 

 20 X 1 0** colony -forming organisms . 

 Filled circles represent the controls; tri- 

 angles, the irradiated cells. 



A good place to start the discus- 

 sion would be to consider some of the ex- 

 periments done by Billen et al. (1) They 

 have observed an inhibitory effect on 

 respiration in E. coli with exposures as 

 low as 5, 000 r. This effect varies with 

 the carbon source in the medium. (Fig- 

 ure 1). 



They observed a period of normal 

 respiration in the B/r strain in every 

 instance. This was longer with succinate 

 or pyruvate than with glucose as the sub- 

 strate. However, in the Texas strain, 

 the difference was in the opposite direc- 

 tion. When the substrate was pyruvate, 

 respiration was inhibited immediately. 

 The length of the period of normal respi- 

 ration was a function of temperature. 

 When the cells were incubated at 26°C, 

 respiration stayed at the control level 

 for 1 to 2 hours, whereas at 37 C, the 

 period of normal respiration was reduced 

 to 20 to 40 minutes. (Figure 2) 



The explanation advanced was 

 that enzyme synthesis is interfered with 

 by radiation. Under the conditions of 



