182 NUCLEIC ACIDS AND THE NITROGENOUS BASES 



the phosphoric acid radicals of adenine and uracil mononucleotids 

 are not utilized in binding these constituents of the nucleic acid mole- 

 cule together. 



When a Purine Nucleotid is heated with dilute sulphuric acid, phos- 

 phoric acid is liberated rapidly and completely. On the contrary, 

 when a Pyrimidine Nucleotid is similarly treated, phosphoric acid is 

 split off slowly. Yeast nucleic acid yields one-half of its phosphoric 

 acid rapidly, and the remaining half slowly. Now if we compare the 

 relative rates of splitting off phosphoric acid by adenine-uracil dinu- 

 cleotid and by the whole yeast nucleic acid when treated in this 

 manner, we find the relative rates of yielding phosphoric acid are 

 identical. Hence, so far as phosphoric acid is concerned, the nucleic 

 acid molecule consists of two symmetrical parts. Union of the two 

 dinucleotid fractions to form whole nucleic acid does not in the slight- 

 est degree affect the rate of yield of phosphoric acid by the component 

 dinucleotids, and hence, phosphoric acid cannot be concerned in their 

 union, and the phosphoric-acid linkage (2) in the subjoined diagram 

 evidentlv does not exist in nucleic acid. 



(i) 



(2) 



(3) 



The molecule of yeast nucleic acid having thus been shown to 

 consist of two symmetrically constructed halves, so far as phosphoric 

 acid is concerned, it follows that if linkage (3) exists, then linkage 

 (1), which would unite the adenine, and uracil mononucleotids must 

 also exist, but this linkage has been shown not to exist, by the compo- 

 sition of the brucine salt of the adenine-uracil dinucleotid. Hence 

 linkage (3) does not exist either and, in short, no phosphoric-acid link- 

 ages exist which bind molecules of mononucleotid together to form the 

 tetranucleotid yeast nucleic acid. 



Between the two remaining forms of linkage, by the carbohydrate 

 or by the purine or pyrimidine radical it has not yet been possible to 

 certainly decide. P. A. Levene, however, concludes that in Cystosine- 

 uracil Dinucleotid only two possibilities exist, either constituent mono- 

 nucleotids are connected by ribose to ribose, or else by uracil (not by 

 cystosine) to ribose. W. Jones believes yeast nucleic acid to be 

 constituted as follows: 



