182 



J. BADDILEY 



CO-NHj 



N' 



-OH 

 -OH 



CHj-OH 



XLII 



Nicotinamide riboside 



Q 



CO-NHo 



-OH 

 -OH 







N 



N^N 



NHj 



N 



-OH 

 -OH 



0- OH 

 i I 

 CHj-O-P-O-P-O-CHs 

 II II 

 O 

 XLIII 

 DPN 



OCO-NHj 



1 



N' 



u 



N-^N^ 



-OH 

 -OH 



-PO3H, 



■OH 



0- OH 



I I 

 CH2-0-P-0-P-0'CH2 



II II 

 



XLIV 

 TPN 



POjHj 



-1-0 — 



OH 



l-CH-CH-CH-CH-CHs-OPOaHj 



j^N_N. 



Yh.n 



XLV 



Adenosine-2',5'-diphosphate 





hydrolyzed by a dinucleotide pyrophosphatase to give nicotinamide nucleo- 

 side-5'-phosphate. The coenzyme is resynthesized by this enzyme in the 

 presence of ATP. Also it has been shown that TPN may be synthesized by 

 enzymic phosphorylation of DPN. When TPN (XLIV) is hydrolyzed by 

 the pyrophosphatase a diphosphate of adenosine is obtained. This is adeno- 

 sine-2',5'-diphosphate (XLV), since it can be hydrolyzed by a specific 

 5'-nucleotidase to adenylic acid a (adenosine-2'-phosphate) .^''^ 



The coenzyme responsible for the oxidation of cysteinesulfinic acid to 

 cysteic acid is called coenzyme III.^*^ Although not yet isolated pure, ultra- 

 violet spectra of the reduced and oxidized forms of the coenzyme suggest 

 that it is a derivative of nicotinamide riboside. Furthermore, it is rapidly 

 destroyed by a pyrophosphatase; thus, it probably contains a pyrophos- 

 phate residue. The tentative formula, nicotinamide riboside-5'-pyrophos- 

 phate (XLVI) has been assigned to this substance. 



2« A. Kornberg and W. E. Pricer, Jr., /. Biol. Chem. 186, 557 (1950). 



2" T. P. Singer and E. B. Kearney, Biochim. et Biophys. Acta 8, 700 (1952). 



