488 



NIACIN 



2. Triphosphopyridine Nucleotide (TPN) 



CH 



H— C- 



H— C— OH 



H— C- 



H— C- 



O 



-0— P— OH 



O 



O 



H— C— OH 



I 

 H— C '0- 



H— C— OH 

 O H— C 



OH 



CH2— O— P— O— P— O— CH2 



OH 



As depicted in the above formula, TPN differs from DPN only by having 

 an additional phosphate group. The (dose similarity of DPN and TPN 

 became evident in the early work of Warburg and Christian^ and of von 

 Euler's group,^- -^ not only from their chemical similarity but in the simi- 

 larity of their biochemical action. The fact that DPN can be reversibly 

 converted to TPN also strengthens this close relationship.^-"*^ 



Warburg and Christian-' ^ and Karrer and associates^*- *^"^^ investigated 

 the mode of linkage of nicotinamide with the rest of the molecule. These 

 investigations firmly established the pyridinium linkage as shown above. 



However, the exact linkage of the remainder of the components remained 

 uncertain, especially the position of the third phosphate. The rather cum- 



« E. Adler, S. Elliot, and L. Elliot, Enzymologia 8, 80 (1940). 



« A. Romberg, /. Biol. Chem. 182, 805 (1950). 



^4 H. von Euler and E. Adler, Hoppe-Seyler's Z. physiol. Chem. 252, 41 (1938). 



^^ R. Vestin, Naturwissenschaften 25, 667 (1937). 



46 P. Karrer, F. Kahnt, R. Epstein, W. Jaffe, and T. Ishii, Hclv. Chim. Acta 21, 223 



(1938). 

 " P. Karrer, T. Ishii, F. W. Kahnt, and I. von Bergen, Helv. Chim. Acta 21, 1174 



(1938). 

 ** P. Karrer, B. H. Ringier, J. Biichi, H. Fritzsche, and U. Solmssen, Helv. Chim. 



Acta 20, 55 (1937). 

 48 P. Karrer, G. Schwarzenbach, and G. E. Utzinger, Helv. Chim. Ada 20, 720 (1937). 

 ^^ P. Karrer, G. Schwarzenbach, F. Benz, and U. Solmssen, Helv. Chim. Acta 19, 



811 (1936). 

 " P. Karrer and F. J. Stare, Helv. Chim. Ada 20, 418 (1937). 



