Glycolysis and the Pasteur Effect 217 



certain that this is not a preparative artifact. Moreover, we 

 could not find appreciable amounts of phosphofructokinase 

 or of the other glycolytic enzymes in the particles. Almost 

 all of their activities were recovered in the supernatant 

 fraction after high-speed centrifugation (Wu and Racker, 

 1959). As a general phenomenon mitochondrial glycolysis of 

 tumours, though representing the basis of an attractive 

 hypothesis, is in our opinion non-existent. 



There are two features of the metabolism of ascites tumour 

 cells which favour an alternative explanation for their high 

 aerobic glycolysis. First of all, the high potential capacity of 

 the glycolytic enzymes, especially the shght excess of G-3-p 

 dehydrogenase and the preponderance of the transphos- 

 phorylating enzymes permits the effective competition of 

 glycolysis for ADP and Pi. Secondly, although Pi has been 

 demonstrated to be a limiting factor of glycolysis in ascites 

 cells, the apparent intracellular concentration is rather high 

 in reference to the K^^ of Pi for G-3-p dehydrogenase (Wu and 

 Racker, 1959). Even at the lowest Pi concentration observed 

 intracellularly a reconstructed system of glycolysis functions 

 almost maximally. It appears that we are confronted with a 

 problem of availability of intracellular phosphate. Since 

 time does not permit dwelling on this subject matter, it may 

 suffice to propose that {a) compartmentation controls the 

 availability of Pi and other intracellular components, and {h) 

 compartmentation is less rigid in tumour cells than in "nor- 

 mal" cells. It will be of interest to make comparative studies 

 in tumour and normal cells of compartmentation of the type 

 discussed by Prof. Lynen and also to explore some other 

 known phenomena (Cori, 1956) which indicate compartmenta- 

 tion. It is possible also that a diminished rigidity of the intra- 

 cellular structure may find an expression in increased penetra- 

 tion of extracellular phosphate and other compounds which 

 enter with difficulty. Some of these possibilities are being 

 investigated at the present time. 



Whatever the reason for the increased glycolytic rate of 

 tumour cells may be, we believe that this feature should be of 



