PHOSPHORYLATION OF CARBOHYDRATES 177 



by Warburg and his school (4). Lipmann (5) has described a bac- 

 terial enzyme system in which inorganic phosphate is taken up and 

 acetylphosphate is formed as an intermediate of pyruvate oxidation. 

 In both cases the phosphate group taken up during oxidation is 

 transferred by the adenylic acid system to suitable phosphate ac- 

 ceptors. 



The oxidation of pyruvate in various animal tissues is also linked 

 with the uptake of inorganic phosphate, and the same has been 

 shown to be true for certain steps of the citric acid cycle, particularly 

 for the oxidation of succinic to fumaric acid (6). The primary phos- 

 phorylation products formed in these cases have not been identified. 

 In dialyzed and suitably supplemented tissue dispersions or extracts, 

 the inorganic phosphate taken up during oxidation of pyruvate is 

 transferred by the adenylic acid system to glucose, which is con- 

 verted to hexosediphosphate. It was noted, however, that when no 

 glucose was added to the system, a small amount of an easily 

 hydrolyzable phosphorus compound was formed. This compound 

 has recently been identified in our laboratory in collaboration with 

 Dr. Ochoa. In large-scale experiments with dialyzed rat liver dis- 

 persion and with glutamate, pyruvate, or succinate as oxidizable 

 substrate we have isolated inorganic pyrophosphate as the crystal- 

 hne sodium salt. The orthophosphate which disappeared corres- 

 ponded in amount to the pyrophosphate formed. 



It is too early to evaluate the significance of this observation. There 

 is the possibility that the pyrophosphate group occurs in some or- 

 ganic combination which is split during the process of isolation. It 

 is fairly certain, however, that the pyrophosphate does not originate 

 from adenosinetriphosphate, since we have found no enzyme in liver 

 preparations which splits added adenylpyrophosphate to adenylic 

 acid and inorganic pyrophosphate. Another possibility is that the 

 pyrophosphate group has nothing to do with the primary phos- 

 phorylation product which is formed during the oxidation of the 

 substrate, but is the result of phosphorylation of orthophosphate. 



The phosphorylation of glucose and other phosphate acceptors 

 which is connected with the oxidation of pyruvate has been termed 

 "aerobic phosphorylation" to signify that the energy for the forma- 

 tion of the phosphate bond comes from oxidations. Table 1 illustrates 

 the quantitative relationship between oxygen consumption and 

 phosphorylation. 



This experiment shows that the dialyzed heart extract supple- 

 mented with magnesium ions, inorganic phosphate, and a trace of 



