INTERMEDIATE CARBOHYDRATE METABOLISM 



11 



the oxidation of phosphoglyceraldehyde* to phosphogly eerie aeid. 

 Even in the presenee of a stoichiometric amount of cozymase, which 

 is simultaneously reduced, the reaction would proceed completely in 

 the direction of oxidation but for the coupling with phosphate up- 

 take by the adenylic system. Thereby a measurable equilibrium is 

 obtained, which was established in 1938 (23) in the Heidelberg Insti- 

 tute and which is shown in Figure 2. The kinetic nature of this 

 equilibrium can be neatly demonstrated by the use of radioactive 

 phosphorus. If radioactive inorganic phosphate is added to the 

 enzymatic mixture after the equilibrium has been established, the 

 adenosinetriphosphate in the solution rapidly takes up radioactive 



loV 



2.0 



1.5 



1.0 



0.5 



\ 

 \ 

 \ 

 \ 

 \ 



to 2040 



C O O 



150 



10 



Figure 3. — Use of radioactive phosphate in the reversible coupling reaction 

 Left: Adjustment of the equilibrium of the coupling reaction; Right: Adjust- 

 ment of the equilibrium of the isotopes 



phosphate, although no chemical change takes place (24), as shown 

 in Figure 3. This reversible coupling reaction was confirmed and ex- 

 plained by Warburg, Christian, and Negelein in the way shown in 

 Figure 4. They isolated the 1, 3-diphosphoglyceric acid as inter- 



* This substance is identical with tlie d-component of the "Fischer-Baer 

 ester" (Chem. Ber. 65, 337, 1932). 



