282 LECTURE XIII. 



and has the following structural formula: 



HN - C . NH 2 



I II 

 CO CH 



I I 

 N = CH 

 Cytosine = 6-amino-2-oxypyrimidine 



Carbohydrates in fact mostly pentoses have also been obtained 

 from the nucleic acids in conjunction with the purine, and pyrimidine bases, 

 and phosphoric acid. Such a typical pentose is xylose. Yeast nucleic acid 

 is supposed to contain an hexose. It is also assumed that an hexose par- 

 ticipates in the constitution of the thymus nucleic acid. Lsevulic acid 

 is obtained therefrom by an energetic decomposition. 



It has recently become questionable whether all of the above com- 

 pounds are to be regarded as primary cleavage-products of the nucleic 

 acids. Steudel l has shown it to be probably true that adenine and guanine 

 are the only primary building stones of the purine bases, and thymine 

 and cytosine of the pyrimidine bases. Hypoxanthine, xanthine, and 

 uracyl are formed secondarily by oxidation in the breaking down of the 

 nucleic acids. This discovery lessens the value of the numerous inves- 

 tigations concerning the purine and pyrimidine bases in the different 

 nucleic acids. It also explains why different authors have obtained 

 divergent results in the study of nucleic acids from the same source. 

 Although this indicates a great gap in our knowledge concerning the 

 amount of individual building stones present in the nucleic acids, which 

 can be filled only by the assumption of secondary transformations, still 

 on the other hand, it is very good news to find that Neuberg and Brahn 2 

 and Bauer 3 have succeeded in clearing up the constitution of inosic acid. 

 From the latter, one molecule each of hypoxanthine, phosphoric acid, 

 and xylose or arabinose is always obtained. It is at present an open 

 question whether the purine bases here observed are to be regarded as 

 of primary or secondary formation, and whether perhaps adenine is not 

 here also the primary building stone. The question that next arises is 

 with regard to the way the components of the nucleic acids are held 

 together in the molecule. Undoubtedly this again will only be answered 

 when synthesis has established the relations. 



Burian 4 attempted to decide how the purine bases are held in the 

 nucleic acid molecules. In one case he based his observations upon the 

 fact that the purine bases, unlike the other components of the nucleic 



1 H. Steudel: Z. physiol. Chem. 49, 406 (1906). 



2 C. Neuberg and B. Brahn: Biochem. Z. 5, 438 (1907). 



3 Friedrich Bauer: Beitr. chem. Physiol. Path. 10, 345 (1907). 



4 R. Burian: Ber. 37, 696 and 708 (i904); Z. physiol. Chem. 42, 297 (1904). 



