THE METABOLISM OF THE PURIN BODIES 391 



remembered, however, that uric acid is only the highest oxida- 

 tion product of a whole series of organic substances, several of 

 which occur in the tissues and are common ingredients of our 

 food-stuffs. The most important of these bodies, besides uric acid, 

 are hypoxanthin, xanthin, adenin, guanin, caffein, theobromine, 

 and thein. The first four of these occur both in the tissues and 

 the food, the last three only in food. These substances are called 

 purin bodies because they all contain, as their nucleus of con- 

 struction, a body called purin. This has the empirical formula 

 C 5 H 4 N 4 . By placing beside it the formulse of the other members 

 of the group, their relationships to one another are clearly 

 seen : 



Purin, C 5 H 4 N 4 

 ( Hypoxanthin, C 5 H 4 N 4 O 

 Purin bases Adenin, C 5 H 4 N 4 - NH 

 1 Xanthin, C 5 H 4 N 4 O 

 iGuanin, C 5 H 4 N 4 O - NH 



Thein and Caffein, C 5 H(CH 3 ) 3 N 4 O 2 



Theobromine, C 5 H 2 (CH 3 ) 2 N 4 O 2 



Uric acid, C 5 H 4 N 4 O 3 



Purin is only of theoretical interest. Of the others, hypo- 

 xanthin, xanthin, and uric acid may be considered as oxides of 

 purin, adenin as hypoxanthin in which the oxygen atom is 

 replaced by an amido group, and guanin as xanthin with one 

 oxygen atom replaced by an amido group. In thein and caffein 

 all three of the hydrogen atoms of xanthin are replaced by 

 methyl groups, and in theobromine two of them are thus 

 replaced. 



Adenin and guanin are constituents of nucleic acid, in which 

 they are in combination with phosphoric acid and usually with 

 a carbohydrate group. Nucleic acid is further combined with 

 albumin to form the nuclein of the tissues. In the nuclein of 

 the thymus gland adenin is most plentiful, whereas that of the 

 pancreas contains almost exclusively guanin. By the break-down 

 of the nucleins in the tissues, adenin and guanin lose their amido 

 groups and become converted into xanthin and hypoxanthin. 

 In their further passage through the organism these bodies are 

 mostly oxidised to uric acid, and as this they are excreted in 

 the urine. The methyl purins, when they are taken into the 

 organism, lose their methyl groups and become converted into 



