IV. BIOCHEMICAL SYSTEMS 489 



bersome isolation procedure used by Warburg (p. 482) and the small yields 

 inhibited research on this subject. However, as improved methods of pre- 

 paring TPN were developed, the subject was again attacked so that the 

 structure has now been clarified to some extent. 



Two principal possibilities were considered. One that the three phos- 

 phates were linked in a chain^- or, as later suggested by Schlenk et al.^^ 

 that the third phosphate group was attached to the pentose of the adenosine 

 portion of the molecule. This matter was not definitely settled until Rom- 

 berg and associates^"* • ^^ subjected TPN to the action of a nucleotide pyro- 

 phosphatase which split the coenzyme into two fragments, nicotinamide 

 ribose phosphate and a diphosphoadenosine fragment which was not adeno- 

 sinepyrophosphate. Kornberg and Pricer^^ were then able to hydrolyze 

 specifically the phosphate esterified to carbon 5 of the diphosphoadenosine 

 fragment leaving an adenosinemonophosphate. They then compared this 

 monophosphate derivative to known samples of adenylic acid "a" and 

 adenylic acid "b."^^- ^^ Kornberg and Pricer could show that the mono- 

 phosphate compound from TPN was not adenyhc acid "b" and was indis- 

 tinguishable from adenylic acid "a." This finding has been confirmed 

 independently by Wang ei al}^ Adenylic acids "a" and "b" were thought 

 at first to be adenosine-2-phosphate and adenosine-3-phosphate, respec- 

 tively, but this is now uncertain.^"- ^^ The 2 and 3 positions of ribose seem 

 the only likely places where the third phosphate could be attached, since 

 carbon 1 is in a glycosidic linkage with adenine, carbon 5 is esterified wdth 

 the second phosphate, and carbon 4 is part of a furanose ring. However, 

 the formula as shown above must be regarded as tentative until the struc- 

 tures of adenylic acid "a" and "b" are proved. 



h. Properties 



Many of the properties of TPN have already been listed (see Table VIII). 

 In general its properties are similar to DPN. It has the same absorption 

 spectrum. This might be expected, since the phosphates contribute little 

 to absorption in the usual ultraviolet range. As with DPN, the absorption 

 at 2G0 m^u is due principally to the adenylic acid moiety.*' "^ Nicotinamide 



*^ H. von Euler and F. Schlenk, Hoppe-Seyler's Z. physiol. ('hem. 246, 64 (1937). 

 " F. Schlenk, B. Hogberg iind S. Tingstam, Arkiv Kemi, Mineral. Geol. 13A, No. 11 



(1939). 

 " A. Kornberg, J. Biol. C'hem. 174, 1051 (1948). 

 " A. Kornberg and W. E. Pricer, Jr., ./. Biol. Chem. 182, 763 (1950). 

 56 A. Kornberg and VV. E. Pricer, Jr., ./. Biol. Chem. 186, 557 (1950). 

 " C. E. Carter, J. Am. Chem. Soc. 72, 1466 (1950). 

 iis W. E. Cohn, /. Am. Chem. Soc. 72, 1471 (1950). 



^3 T. P. Wang, L. Shuster, and N. O. Kaplan, J. Am. Chem. Soc. 74, 3204 (1952). 

 6" D. M. Brown and A. R. Todd, J. Chem. Soc. 1952, 44. 

 " D. M. Brown, O. I. Magrath, and A. R. Todd, /. Chem. Soc. 1952, 2708. 



