VOL. 4 (1950) METABOLISM OF NUCLEATED RED CELLS 289 



DISCUSSION 



5. Mechanism of the aerobic glycolysis in the hemolysate 



On the basis of our expeiiments we can draw the conclusion that the aerobic 

 metabohsm in nucleated erythrocytes consists of several distinct enzymatic systems. 

 If no glucose is added to the hemolysate no significant amounts of preformed hexoses 

 are available for oxidation, but adenosine-5-phosphate, derived from ATP, breaks 

 down and its ribose disappears. This process and oxidation of fat and protein should 

 be responsible for the observed respiration of the hemolysate in absence of glucose. 

 The increase after addition of glucose can be traced again to at least two different 

 reactions, namely, complete oxidation to CO2 and oxidation of glucose to a phosphoric 

 ester, whereby one atom of oxygen combines with one mol of glucose. It is probable 

 that the latter reaction consists in the oxidation of glucose to phosphogluconic acid. 



The powerful aerobic glycolysis in the hemolysate in presence of glucose can be 

 due to the fact that the oxidation of one molecule of glucose is coupled with the phos- 

 phorylation of many molecules of this sugar and the triosephosphate dehydrogenase 

 is much more efficient in the hemolysate than the system oxidizing pyruvate. The 

 excess of the latter is therefore reduced to lactic acid. As the hemolysate contains the 

 enz5nne system of the tricarboxylic acid cycle it is reasonable to assume that the oxida- 

 tion of glucose to CO2 goes over this cycle. It is known from experiments on other tissue 

 extracts that the oxidation of i mol of glucose in this way can be coupled with the 

 phosphorylation of 18 molecules of glucose to hexose diphosphate. This would explain 

 the fact that the addition of all those acids which increase the turnover of the Krebs 

 cycle, and of Mg which is an activator of the oxidation of pyruvic acid, considerably 

 increases the aerobic glycolysis. 



The inability of the hemolysate to glycolyse anaerobically can be explained easily. 

 The hemolysis of nucleated erythrocytes is accompanied by an explosive increase in 

 the activity of ATPase. At room temperature practically all of ATP originally present 

 in the cells is dephosphorylated in a few minutes; the glycolysis of one molecule of 

 glucose can maximally resynthesize 2 molecules of ATP. As long, therefore, as the 

 speed of the simple dephosphorylation of ATP exceeds the speed of transphosphoryla- 

 tion with glucose the latter process must stop in anaerobiosis due to the total disappear- 

 ance of ATP. The efficiency of the oxidative breakdown of glucose as far as synthesis 

 of ATP is concerned makes it possible to keep up under aerobic conditions a certain 

 minimum concentration of ATP necessary for the phosphorylation of glucose. This 

 amount, however, is very small, even under aerobic conditions, and not detectable 

 by the usual colorimetric procedures of determination. 



Point of attack of ions 



The realization of this multitude of enzymatic processes involved in the aerobic 

 metabolism is important for the consideration of the possible mechanism of the inhibi- 

 tory effects of ions on this metabolism. It appears significant that all ions, cations as well 

 as anions, are able to suppress not one but many of the enzyme reactions constituting 

 the oxidative metabolism. On the other hand, the degree of inhibition is different for 

 different enzyme reactions or systems of reactions. The aerobic glycolysis is in general 

 more strongly inhibited than the oxidation of glucose, which in turn suffers more than 

 the O2 consumption without glucose. The oxidation of succinate and a-ketoglutarate 

 References p. zgz. 

 19 



