252 Van R. Potter and Hermann Niemeyer 



form of the coenzyme decreased glycolysis, an effect that was 

 enhanced markedly by the simultaneous addition of liver 

 mitochondria, which can oxidize the TPNH. 



The results are explained by an accumulation of 6-phospho- 

 gluconate, which inhibits phosphohexoisomerase. This block 

 would permit an accumulation of glucose-6-phosphate which, 

 in turn, would inhibit hexokinase. The relative activities of 

 glucose-6-phosphate and 6-phosphogluconic dehydrogenases 

 and the presence of a TPN-lactic dehydrogenase in the system 

 contribute to the operation of this mechanism. 



Note added in proof. The following summary of data relevant to our findings 

 is taken from a recent publication (Neufach, S. A., and Melnikova, M. P. 

 (1958). Biochimia, 23, 4>40): 



"It is assumed that rates of glycolysis may be determined by different 

 factors under varying functional conditions of the cell and varying levels of 

 glycolysis. The maximal level for rates of glycolysis in muscle in situ (about 

 1500 (J.M lactic acid per g. per hour) can be reproduced in vitro by means of a 

 reconstructed system consisting of dialysed muscle extract ATP, DPN, Mg2+, 

 F-di-P, orthopiiosphate, nicotinamide, cysteine and glycogen. When the 

 rate of glycolysis follows a linear course, the "slowest" enzyme of glycolysis 

 may be identified directly by the acceleration of the process which occurs on 

 introducing the purified enzyme. It is shown that none of the enzymes, 

 aldolase, 3-phosphate dehydrogenase or lactic dehydrogenase, hitherto 

 believed to to be the slowest enzymes of glycolysis, act as such in reality when 

 their activity is displayed in a medium with sufficient coenzyme content. 

 This is the condition prevailing in the body when muscle work is highly 

 active. Depending on the value of 6-phosphofructokinase power, a 4- to 8-fold 

 increase in the rate of glycogen disintegration follows, when purified PFK is 

 introduced. Linear growth of the effect accompanies increasing increments of 

 PFK. The rate of glucose disintegration may even increase to 10-14 times the 

 original value when purified hexokinase has been introduced. The same result 

 has been obtained with a fresh, non-dialysed muscle extract. 



It is suggested that, while the rate of glycolysis in skeletal muscle does 

 depend upon PFK power, it is a function of hexokinase in nervous tissue, 

 heart, erythrocytes and tumours." 



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AiSENBERG, A. C, and Potter, V. R. (1957). .7. biol. Chem., 224, 1115. 

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 Barker, S. B., and Summerson, W. H. (1941). J. biol. Chem., 138, 535. 

 BoNSiGNORE, A., Pontremoli, S., and Vergnano, C. (1957). G. Biochim., 



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