Discussion 189 



Schmidt-Thannhauser method to a whole tissue but to extracted nucleic 

 acid, which is a very different thing. 



Brown: The experiment I am now quoting was done by an older 

 technique, which was to use desiccated tissue which had been extracted 

 with fat solvent and trichloracetic acid. 



Davidson: In such an experiment there might well be the additional 

 phosphate ester. 



Leblond: I wanted to clarify the meaning of the curve of Dr. Szafarz. 

 In your interpretation of that slope, do you mean that all the radio- 

 activity comes in at the beginning, and then when particles duplicate 

 themselves they retain the same activity, and since they increase in 

 quantity, the radioactivity per particle decreases? 



Szafarz: In the beginning all the fractions of the ribonucleic acid are 

 marked equally and have the same specific radioactivity. Then at the 

 beginning of this graph we add non-labelled phosphate. At that time 

 the culture begins to grow again and the cells multiply exponentially, 

 so the specific activity of the RNA begins to decrease. If we try to 

 establish a relation between the specific radioactivity and the quantity 

 of RNA we see that this regularity in the slope of the specific 

 radioactivity doesn't correspond to the evolution of the quantity of 

 RNA. The quantity of RNA doesn't begin to increase just at the 

 moment when the specific radioactivity begins to decrease. If we 

 plot the quantity of protein synthesized, the proteins begin to in- 

 crease at the same time. We have found this behaviour of RNA in 

 all our experiments. In the beginning we thought it was a mistake, but 

 we regularly find the same thing. So the specific radioactivity is inde- 

 pendent of the quantity of RNA present, and this can be explained 

 by assuming that the quantity of RNA synthesized is at any instant 

 proportional to the quantity of RNA present. It is an autocatalytic 

 multiplication. 



Popjak: In connection with the differences of the specific activities 

 of the nucleic acid fractions found in the large and small granules, 

 it might be worth mentioning that Mr. Ada, who worked in Dr. 

 McFarlane's laboratory some years ago, studied with ^^p the phospho- 

 lipid turnover in the mitochondria and microsomes of the liver cell. 

 He found that the specific activity of the phospholipids of the micro- 

 somes was always higher than that of the mitochondria. The two types 

 of particles seem to have been quite independent of each other as 

 regards phospholipid metabolism. 



