508 URIC-ACID METABOLISM AND GOUT 



It should also be mentioned that not all of the purin bases 

 of the body is bound in the form of nucleic acid. A consider- 

 able amount is present in a free condition, or at least not bound 

 in nucleic acid, especially in muscle tissue, where much more of 

 the purin bases is free than combined. Uric acid can be 

 formed equally as well from the free purin bases as from purin 

 bases liberated from nucleic acid indeed, evidence has recently 

 been brought forward indicating that a large proportion of the 

 uric acid arising during metabolism (endogenous) comes from 

 the free hypoxanthin of the muscles. 



As to the place where uric acid is formed, it seems probable 

 that the purin bases and the necessary oxidative enzymes are 

 present in many if not in all varieties of cells ; certainly all 

 the chief visceral tissues and the muscles are capable of form- 

 ing uric acid. 



DESTRUCTION OF URIC ACID 



By no means all of the purin bases that is formed in the 

 tissues, or that is taken into the alimentary canal in the food, 

 appears in the urine as uric acid ; by far the greater part is des- 

 troyed through oxidation, forming urea from the nitrogen-con- 



taming groups, and oxalic acid, from the remaining C 



C 



in case oxidation is not complete. The relation of uric acid to 

 urea can readily be seen by comparing their structural formulae : 



H 2 N HN C = O 



O=C O=C C NH 



I I II >c=o 



H 2 N HN C NH 



(urea) (uric acid) 



Of the purin bases taken in the food, it is estimated that 

 in carnivora, such as dogs, but one-twentieth to one-thirtieth 

 appears in the urine as uric acid ; in herbivora (rabbits), one- 

 sixth ; and in omnivora (man), one-half. Apparently the purin 

 bases taken in the food are first converted into uric acid before 

 being destroyed, for it has been found that if uric acid is injected 

 into an animal, the same amount appears in the urine as when a 

 corresponding quantity of purin bases is given to the same ani- 

 mal by mouth or subcutaneously. 



