NICOTINAMIDE NUCLEOTIDE ENZYMES 115 



with any of the typical reagents used in nucleotide chemistry, such 

 as picric acid, picrolonic acid, Reinecke salt, chloroplatinate, and 

 aurichloride. It is difficult, therefore, to remove the last traces of 

 impurities from the nucleoside preparations. The elementary analysis 

 and the quantitative determination of nicotinamide and pentose, 

 however, rule out every other composition except that of a pentose 

 nucleoside. It remains to be determined what pentose we are deal- 

 ing with; for this purpose relatively large amounts of the nucleoside 

 must be prepared, a task which is in progress at present. 



It was of great interest to compare this split product with the 

 model substances of P. Karrer. It was found to be strikingly similar 

 to the synthetic compounds in all respects. In the first place, the 

 reduction with sodium hydrosulfite should be mentioned (see for- 

 mula 5). 



FORMULA 5 



fT^ 



CONH 



KJ ^ 



CONH 



I A I 



Pentose Pentose 



Like the codehydrogenases and the synthetic pyridine derivatives 

 with pentavalent ring nitrogen, the nicotinamide nucleoside yields 

 an o-dihydro compound which has the same characteristic absorp- 

 tion maximum at 340 m[x (see Figure 2). In other respects also the 

 nucleoside has the expected properties. It has in the oxidized form 

 a stability optimum of about pH 3-4, and is extremely labile in 

 alkali, whereas the dihydro derivative is stable in alkali and is 

 sensitive toward acids, as are the dihydro coenzymes. Alkaline as 

 well as acid hydrolysis separates the carbohydrate from the nico- 

 tinamide. 



The nucleoside cannot replace either of the coenzymes in the 

 dehydrogenase systems. The phosphoric acid and adenylic acid 

 which are present in the codehydrogenases are necessary for the 

 combination of the pyridinium compound with the apoenzymes. 



The investigations of Warburg and Karrer, described above, on 

 the linkage between nicotinamide and the rest of the molecule, 

 which were completed by the isolation of the natural nicotinamide 

 nucleoside, justify the claim of a quaternary pyridinium linkage. 

 Beyond this, our knowledge on the combination of the structural 



