506 URIC-ACID METABOLISM AND GOUT 



the pigments, also aid in its solution. How the uric acid 

 is kept in solution in the blood is not exactly understood, but 

 it seems probable that it is in combination with some organic 

 substance, possibly with some derivative of nucleic acid. 



FORMATION OF URIC ACID 



The origin of uric acid is chiefly, although not exclusively, 

 from the nucleoproteids, and it is customary to refer to uric 

 acid formed from the nucleoproteids of the foods as " exogen- 

 ous " uric acid, in contrast to the " endogenous " uric acid that 

 is formed from the nucleoproteids of the body cells during 

 their catabolism. 



This may be readily explained by a brief consideration of 

 the composition of the nucleoproteids. The nucleoproteids may 

 be looked upon as salts formed through combination of proteids 

 with nucleic acid. Nucleic acid in turn is a compound of 

 phosphoric acid with purin bases, pyrimidin bases, and usually 

 also with carbohydrate radicals. For example, the following 

 structural formulae have been proposed as indicating the com- 

 position of certain nucleic acids, showing (provisionally) how 

 pentose radicals (C,H 9 O 5 ) purin radicals (C 5 H 4 N 5 and C 5 H 4 N 5 O) 

 and pyrimidin radicals (C 4 H 3 N 2 O 2 ) may be grouped about phos- 

 phoric-acid radicals to form various nucleic acids : 



OH OH OH OH OFT 



\ / \ / / 



C 5 H 9 5 - P - C 5 H A C 5 H 4 N 5 - O - P - O - C 3 H 5 \ 



I I C 5 H 9 5 



O O 



HO. \ /OH 



X P-C 4 H 3 N A C 5 H 4 N 5 - O - P - O - C 3 H 5 / 



X' | X C 5 H 9 5 



O 00 



! /OH \/ /OH 



HO P< C 5 H 4 N 5 O - P O C 3 H 5 



I 

 C 5 H,N 6 -0 P x -OH 



OH OH OH 



Triticonucleic acid (from wheat germ) Guanylic acid (from pancreas) 



Nucleic acids of different origins differ from one another in 

 the number and variety of purin bases they contain, and also 

 in their carbohydrate radicals, hence an almost infinite variety 

 of nucleic acids and nucleoproteids may exist. 



Uric acid itself does not exist in the nucleoproteid molecule, 



