CHEMISTRY OF NUCLEIC AC J I) V,2\) 



to the "endogenous" uric acid tliat is lormed from the imclco-|)r()t(!ins 

 of the body cells during their catabolism. This may be readily 

 explained by a brief considciration of the composition of the nudeo- 

 proteius. The nucleoprotcins may be looked upon as salts formed 

 through combination of proteins with nucleic acid. Nucleic acid in 

 turn is a compound of phosphoric acid with purine bases, pyrimidine 

 bases, and carbohydrate radicals, constituting a complex sort of glu- 

 coside. 



A long series of careful analytical studies has at last shown us that 

 nucleic acids, are, whatever the source, quite similar in composition, 

 consisting always of a complex containing phosphoric acid, the two 

 amino purines (adenine and guanine), two pyrimidines (either cyto- 

 sine and uracil or cytosine and thymine); and a carbohj'drate, which 

 may be either a pentose or a hexose. Apparently there arc two sorts 

 of nucleic acids, one from plants, wliich contains always uracil and 

 pentose, and one from animal tissues, containing instead thymine and 

 a hexose. So constant are the findings in regard to these compounds 

 that it has seemed feasible to consider their manner of union in the 

 intact nucleic acid molecule, and Levene and Jacobs have proposed as 

 the structure of thymus nucleic acid the following arrangement : 

 H PO3— C6H10O4— CsHsNsO 



I (guanine group) 



o 



H2PO4 -CeHsOo— C5H5N2O2 



I (thymine group) 



o 



I 



H2PO4 -CsHsOo— C4H,N30 



(cytosine group) 



o 



I 



H PO3 — C6H10O4 — C6H4N6 



(adenine group) 



It will be seen that this proposed formula postulates in the nucleic 

 acid molecule, one radical of each of the two purines and pyrimidines, 

 each of these being united by a carbohydrate radical to a phosphoric 

 acid radical. Recognizing that this must be looked upon as a provi- 

 sional formula,^" it will serve as a base of departure from which to 

 consider the metabolism of nucleic acid. 



The grouping of hexose + purine or hexose + pyrimidine is re- 

 ferred to as a "nucleoside," analogous in terminology to "glucoside." 

 The same groupings plus the phosphoric acid radical constitute the 

 "nucleotids," nucleic acid thus being made up of four nucleotids. 

 Emil Fischer has reported^^ the synthetic production of a nucleotide 

 composed of phosphoric acid united to a glucoside of theophyllin, this 



" Jones and Read (Jour. Biol. Chem., 1917 (29), 111) have advanced evidence 

 to indicate that the linkage between the nucleotids is between the carbohydrate 

 radicals rather than between the phosphoric acid groups. See also Thannhauser 

 and Dorfmiiller, Zeit. physiol. Chem., 1917 (100), 121. 



" Sitzungsber. k. .\kad. Wissensch., Berlin, 1914 (33), 905. 



