636 



METABOLISM 



By milder oxidation by means of potassium permanganate in the 

 cold, uric acid becomes quantitatively converted to allantoin: 



C 5 H 4 N 4 3 + H 2 + = C 4 H 6 N 4 3 + C0 2 . 

 (uric acid) (allantoin) 



The importance of this transformation lies in the fact that in most 

 animals, man and the higher apes being exceptions, uric acid is thus 

 decomposed in the animal body. The structural formulas for the other 

 purine bodies in relationship with those of purine and uric acid are given 

 below. 

 Purine itself has the following structural formula: 



IN 

 I 



Cc H 



I 

 O - NHr 



C8- II 



I! I! / 



sN - O - N 

 (For convenience of description the atoms in purine are numbered as shown.) 



HN-C=0 



I I 

 H- C C-NH 



O 



HN-C=O 

 C-NH 



=<! 



C-H 



N - C - N 

 (hypoxan thine) (6-oxypurine) 



N = C-NH 2 



I 



H - C C-NH 



I 



HN-C- N 

 (xanthine) 



HN-C=0 

 H 2 N = C C-NH 



C-H 



(2-6-oxypurine) 



I 



C-H 



/ 



\ 

 / 



C-H 



-C- N N-C- N 



(adenine) (6-amino-purine) (guanine) (2-amino-6-oxypurine) 



HN-CO 



OC C-NH 



I li \ 



CO 



HN- C -NH 



Uric acid (2-6-8-trioxypurine) 



The substances with which the purine bases are most closely related 

 are the pyrimidine bases. Three of these are known: 



cytosine ( N = C-NH 2 



I 

 CO CH 



thymine (NH-CO 



I ! 

 CO C.CH 3 



and uracil (NH-CO 

 CO CH 



NH-CH 



NH-CH) ; 



NH-CH). 



