222 Arne Forssberg 



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DISCUSSION 



Poj)jak: I would like to make some comments regarding the rate of 

 metabolism of ascites tumour cells, and the deductions one might make 

 when measuring metabolic events in vivo compared to in vitro. Prof. 

 Davidson mentioned that in vitro he gets excellent labelling with ^ap or 

 with adenine, but no evidence for purine synthesis. In vivo, on the other 

 hand, you get labelling from glycine and from formate. I feel that the 

 in vivo labelling from glycine and from formate may not necessarily 

 mean that purine has been synthesized within the ascites cell. We 

 thought the ascites cell was a very convenient preparation for measuring 

 certain problems of fat metabolism. We carried out some in vitro 

 incubations, and found only minute traces of synthetic ability of these 

 ascites tumour cells, e.g. in vitro they cannot synthesize fatty acids 

 from acetate under conditions of, say, liver slices or mammary gland 

 slices ; that relates to your figures for acetoacetic acid. Dr. Forssberg. 

 They can hardly oxidize acetate to CO 2, from which I must assume that 

 the citric acid cycle is working at a very poor rate indeed. I wonder 

 whether some of the in vivo incorporation data that one observes with 

 the ascites tumour might not be due to the fact that the compounds are 

 synthesized elsewhere and then transferred, because in the case of lipids, 



