99 



DUBOIS: No, the characteristics of the enzyme splitting ATP in 

 spleen seem to be different from those of liver. For one thing, the activation 

 curves with calcium and magnesium are identical. If we replace calcium with 

 manganese the activity is much lower. 



Analysis of the residue after incubation shows that the ATP is convert- 

 ed mainly to ADP. The phosphorus liberated has cotne from the single reaction 

 consisting of the conversion of ATP to ADP. There is no appreciable kinase 

 present and as a result, very little adenylic acid is formed. The sum of the 

 residual ATP, ADP and adenylic acid accounts for the original amount of sub- 

 strate. 



POTTER: I don' t think you have latent ATP-ase in the spleen. If you 

 consider that this effect is not due to a changing cell population, then you have 

 to start considering an increased amount of enzyme. 



DUBOIS: We do not believe that this is entirely explainable on the basis of 

 cell population but we still need to do additional experiments on that aspect of 

 the problem. This effect does not occur in liver, brain, heart, kidney or other 

 radioresistant tissues regardless of the X-ray dose. 



A point of interest is that the rate of hydrolysis of ADP by homogenates 

 of irradiated spleen is not increased to nearly the same extent as the hydrolysis 

 of ATP. 



CHARGAFF: You have based it all on the amount of tissue. If you did 

 it on the nucleai' count or the DMA would it look the same? Did you get the same 

 type of increase if you took another base line? 



DUBOIS: It has been done on the basis of nitrogen and the increase is 

 still obtained. That was done by Ashwell and Hickman (10). It has not been 

 done in terms of DNA. 



KAPLAN: This is a very pertinent question because Leonard Cole 

 has recently shown that if you compare splenic weight reduction on a mg. basis 

 with the reduction in DNA content of the whole spleen following radiation, there 

 is a far greater decrease in DNA content than one can account for by change in 

 weight. In other words, the number of nuclei left are far fewer than the weight 

 change would lead you to believe because the most radiosensitive cells are the 

 smallest cells. There are a lot fewer nuclei and fewer cells in those spleens 1, 

 3 and 5 days after irradiation than there were before. 



SPIEGELMAN: If this is true, the other enzymes should go up. It 

 does not seem likely that this type of explanation is going to be the answer. 



KAPLAN: No, but this is still a better way of expressing it. 



SPIEGELMAN: Yes, I will agree with you, but I think that probably 

 you will not iron out this difference if he does not see it with other enzymes. 



DUBOIS: And we don't with the enzymes that have been studied. To 

 proceed with the discussion, the question of the influence of radiation on oxida- 

 tive phosphorylation by the spleen should, perhaps, be mentioned. Although 

 there is a decrease in phosphorylation by spleen homogenates and preparations 

 of spleen tissue, I think the increase in adenosine triphosphatase activity is a 

 complicating factor and that we should now re-examine the phosphorylation 

 picture. One reason for this is that in the phosphorylation setup that is ordinari- 



