190 UNITY AND DIVERSITY IN BIOCHEMISTRY 



7. After the first transfer of phosphate described in 6, 3-phospho- 

 glyceric acid is left. In the presence of phosphoglyceromutase and 

 2,3-diphosphoglyceric acid as coenzyme (see p. 175) an isomerization to 

 2-phosphoglyceric acid occurs. 



8. It is at the level of 2-phosphoglyceric acid that the second internal 

 oxido-reduction appears. In the presence of enolase and Mg++, a molecule 

 of water is removed and a molecular rearrangement generates (see p. 143) 

 an energy-rich bond. 



CH.OH CH2 



I II 



HC— OPO(OH)2 ^ C— 0'-P0(0H)2 + H2O 



I I 



COOH COOH 



2-phosphoglyceric acid phosphoenolpyruvic acid 



9. The phosphoenolpyruvic acid is the subject of the second transfer 

 of phosphate, in the presence of pyruvic phosphokinase, a phosphokinase 

 acting almost at equilibrium (low AF) the transfer is brought about with 

 conservation of the energy-rich bond. 



COOH COOH 



I I 



COPO(OH)o -f ADP?=^ COH + ATP 



CO 



I 



CH, 



pyruvic acid 



10. The pyruvic acid, in the presence of pyruvic carboxylase (the 

 prosthetic group of which is DPT) and Mg++, is decarboxylated to 

 acetaldehyde. 



Mg++ 

 CH3— CO— COOH -> CH3— CHO + CO2 



DPT 



11. When the 1,3-diphosphoglyceric acid is formed, in reaction 5, 

 DPN+ is reduced. The DPNH which results is first of all dehydrogenated 

 by phosphodihydroxyacetone producing 3-phosphoglycerol, which is then 

 hydrolysed by a phosphatase to form glycerol. This is the explanation of 



