206 E. Racker and^R. Wu 



here in detail. It may suffice to say that we have simulated 

 phenomena such as the Pasteur and Crabtree effects in arti- 

 ficial mixtures of respiring mitochondria and glycolytic 

 enzymes. We have reconstructed a pentose phosphate cycle 

 which oxidizes all six carbons of glucose-6-phosphate (Couri 

 and Racker, 1958, unpublished) and it has been possible to 

 demonstrate formation of fructose-1 : 6-diphosphate from 

 pyruvate, thus reversing a segment of glycolysis (Krimsky, 

 1959). But we would emphasize that we regard these recon- 

 structed systems as models only, from which we can learn, 

 by variation of their components, how these phenomena might 

 be brought about. In order to gain information as to how these 

 processes are actually accomplished within the cell, we must 

 turn to the cell itself. 



We have chosen for study the ascites tumour cells (Ehrlich, 

 tetraploid) because they exhibit both Pasteur and Crabtree 

 effects and because they are very suitable for metabolic 

 studies. Although various ascites tumours have been exten- 

 sively studied, we have found little information regarding the 

 limiting factors of their carbohydrate metabolism. 



We proceeded, therefore, to explore systematically their 

 enzymes, coenzymes and metabolites. The profile of the 

 glycolytic enzymes in extracts obtained by centrifugation at 

 100,000 g for 30 minutes, and in mitochondrial particles 

 centrifuged down at 10,000 g was determined by measuring 

 enzyme activities under standard conditions at pH 7 • 4 in the 

 presence of excess substrate and coenzymes. The experi- 

 mental data, which are being published elsewhere, can be 

 summarized as follows. The bulk of the glycolytic enzymes 

 was found in the high-speed supernatant solution (extract). 

 Only hexokinase was found to be concentrated in the particles 

 (up to 60 per cent of the total) and to have a specific activity 

 four- to nine-fold that of the extract. Small amounts of phos- 

 phofructokinase and aldolase activity were also associated 

 with the particles; the activities of the other glycolytic 

 enzymes could be accounted for by the amount of trapped 

 supernatant fluid in the washed mitochondria. The profile 



