178 A SYMPOSIUM ON RESPIRATORY ENZYMES 



adenylic acid has practically no basal oxygen consumption and that 

 addition of 2 micromoles of succinic acid, a catalytic amount, has 

 very little effect on oxygen consumption. The addition of 50 micro- 

 moles of glucose had a very marked effect on oxygen consumption, 



Table 1.— Glucose balance in dialyzed heart muscle extract* 



(1 cc. of extract supplemented with Mg"*"*" ions, inorganic phosphate, and a trace of 



adenylic acid. Incubated 60 minutes at 37° C. All values are 



expressed in micromoles.) 



Addition 



Glucose Oxygen Phosphate Total glucose 



disappearing consumed esterified accounted for 



None 1.5 



2 succinate 2.6 



50 glucose + 



2 succinate 24.4 22.3 36.1 3.5+18 = 21.5 



*J. Biol. Chem., 137, 343 (1941). 



and there can be no doubt that glucose was the substrate under- 

 going oxidation. Detennination of the respiratory quotient in other 

 experiments showed that it was unity for added glucose and 1.25 

 for added pyruvate. It is to be noted that an oxygen consumption of 

 22 micromoles corresponds to one-sixth as much glucose, that is to 

 3.5 micromoles, while the glucose which actually disappeared ac- 

 cording to sugar analysis was 24.4 micromoles. The glucose which 

 disappeared without being oxidized was largely recovered as hexose- 

 diphosphate, 36 micromoles of phosphate esterified corresponding 

 to 18 micromoles of glucose. Lactic acid formation was not deter- 

 mined. The balance indicates that for each mole of glucose oxidized 

 an additional 6 moles of glucose disappear, 5 of which are present 

 as phosphate ester. This means that about one atom of phosphate is 

 esterified for each atom of oxygen consumed. Ochoa (7) and Belitzer 

 and Tsibakova (8) observed even higher ratios, namely, from 2 to 3 

 atoms of phosphate esterified for each atom of oxygen consumed. 

 This would indicate that not only the primary removal of hydrogen 

 from the substrate but also one or even two subsequent hydrogen 

 transfers over intermediate catalysts may cause phosphorylation. 



Aerobic phosphorylation is a mechanism by which oxidative 

 energy is utilized in the cell. The oxidative energy is converted into 

 phosphate bond energy, to use Lipmann's (5) terminology, and the 

 adenylic acid system serves as the mediator of this energy transfer. 

 When glucose is the phosphate acceptor, the system, once started, is 



