180 NUCLEIC ACIDS AND THE NITROGENOUS BASES 



There are three conceivable arrangements of the three constituent 

 radicals of Guanylic Acid. They are: 



O 00 



|| II II 



HO P O.CsHsOs.CsI^NaO, C 5 H 9 O4.0 P C 5 H 4 N 5 O, C5H 9 O4.C 5 H3N 5 O P OH 



T k 9 



Of these three arrangements II cannot be the one which actually occurs 

 in guanylic acid, because on neutral hydrolysis under pressure it yields 

 Guanosine C5H 9 O4.C5H4N 5 O, which would be impossible if, in the 

 original molecule, the carbohydrate and basic radicals were separated 

 by the interposition of phosphoric acid. Either I or III must be the 

 correct formula. 



Now on comparing the rates at which phosphoric acid and guanine 

 are liberated from guanylic acid by acid hydrolysis, it is found that 

 guanine is liberated much more rapidly than phosphoric acid. This 

 implies, of course, that during the progress of hydrolysis, while guanine 

 is being split off, phosphoric acid is being held in combination with 

 some other substance from which compound it is detached with relative 

 difficulty. The only substance, guanine being excluded, with which 

 the phosphoric acid can be combined is a-ribose. It follows, there- 

 fore, that phosphoric acid is attached to the molecule through the 

 pentose radical, and formula I must represent the actual arrangement 

 of the groups in guanylic acid. The same reasoning applies to the 

 adenine-uracil dinucleotid which may be split off from yeast nucleic 

 acid by partial enzymatic hydrolysis. We infer, therefore, from these 

 facts and from the general similarity of the various mononucleotids 

 to one another that the arrangement of radicals in all of them is: 

 Phosphoric acid carbohydrate purine or pyrimidine. 



It remains to be considered how these mononucleotid radicals are 

 united together to form the tetranucleotids characteristic, respectively, 

 of vegetable and animal tissues. 



Three alternative possibilities exist, namely, (a) that the mono- 

 nucleotids are united to one another through their phosphoric acid 

 groups, so that the tetranucleotid would be a substituted polyphos- 

 phoric acid. This was the view originally propounded by Kossel and 

 has claimed very general acceptance until quite recently; (6) that the 

 mononucleotids are united to one another through their carbohydrate 

 radicals and (c) that they are united to one another through their 

 purine or pyrimidine radicals. Between the two latter alternatives 

 it has not as yet proved possible to decide with certainty, but the 

 first alternative, that the mononucleotids are united to one another 

 through their phosphoric acid radicals, may be dismissed for the 

 following reasons: 



