496 NIACIN 



complicated process of obtaining energy and building blocks from its nutri- 

 ents or, during anabolic phases of metabolism, of synthesizing appropriate 

 molecules for deposition or incorporation into other tissue substances. Only 

 certain of these steps require the participation of DPN and TPN. Yet, 

 these coenzymes are necessary for the catalysis of steps which are of such 

 importance that, should these reactions be blocked, the cell cannot function 

 and indeed the organism itself cannot survive. 



1. Synthesis of High-Energy Phosphate Bonds 



Phosphoric anhydride compounds such as adenosinetriphosphate occupy 

 a key role in metabolism. They constitute a means whereby the cell can 

 conserve and store energy in a readily transferable form. DPN and TPN 

 are involved in the processes by which these high-energy phosphate bonds 

 are synthesized. For example, if an aldehyde such as 1 , 3-diphosphoglycer- 

 aldehyde is dehydrogenated (i.e., oxidized) by DPN, one of the phosphate 

 groups is converted into a reactive acyl phosphate which can be transferred 

 to adenosinediphosphate (ADP), thus forming adenosinetriphosphate 

 (ATP) as depicted below-i^^-io^ 



H 

 O H H O O 



II III II 



HO— P— O— C— C— C— 0— P— OH + DPN ;:± 



O H O H O 



H H H 



O H H O O 



DPNH2 + HO— P— O— C— C— C— O— P— OH 



OHO 



H H H 



O H H O O 



II I I II II 



HO— P— O— C— C— C— O— P— OH + ADP 



OHO O 



H H H 



O H H O 



II I I II 



ATP + HO— P— 0— C— C— C— OH 



O HO 



H H 



i»* O. Warburg and W. Christian, Biochevi. Z. 301, 221 (1939). 

 106 O. Warburg and W. Christian, Biochem. Z. 303, 40 (1939). 

 i«6 E. Negelein and H. Bromel, Biochem. Z. 303, 132 (1939). 



