624 



URIC-ACID METABOIJ^M A\D GOUT 



reptiles so far examined. The significance of this distribution of iiri- 

 case will be discussed at greater length a little later. 



The following graphic expression of the series of steps leading to 

 the formation of uric acid has been presented by Amberg and Jones:'' 





0--P'-Q CsHjOj Cs HjN, (NHj) 



^u.n.n 



Uric add 



/OH 



C,HN-OH 



oxidcie Xanthine ^ 



adenosine 



[anrhlne 



ypm, 

 C.HjN^O H 



Another possible source of uric acid is through synthesis. In birds, 

 which eliminate most of their nitrogen in the form of uric acid, syn- 

 thesis of uric acid undoubtedly occurs. It must also be considered 

 that young mammals can synthesize the purines necessary for their 

 growth from foods which contain no purines.^*' It would seem pos- 

 sible, therefore, for synthesis of uric acid to occur in adult mammals, 

 but as yet satisfactory experimental evidence is lacking that such 

 synthesis does occur, although an apparently reversed reaction, 

 whereby uric acid destroyed by liver tissue can be resj^nthesized by 

 the same tissue acting upon it in the absence of oxygen, has been de- 

 scribed by Ascoli and Izar.^^ Their work has not been repeated suc- 

 cessfully by others. I have failed in several attempts to secure re- 

 synthesis of uric acid by dog livers, and Spiers/^'' who made a more 

 extensive investigation, was unable to corroborate their findings. 



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

 body is bound in the form of nucleic acid. A considerable amount is 

 present in a free condition, or at least not bound in luicleic acid, espe- 

 cially in muscle tissue. Uric acid can be fonned as well from 

 the free purine bases as from purine bases liberated from nucleic acid 

 — indeed, evidence has been brought forward indicating that a large 

 proportion of the uric acid arising during metabolism (endogenous) 

 comes from the free hypoxanthine of the muscles. 



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

 different animals different organs arc chiefly coiu'erned. for it has 



oZeit. plivsiol. Chvm., 1011 (7.S), 407. 

 lOMK'olluin, .Amcr. .lour. Plivsiol.. 100!) (2r>). 120. 

 11 Sf'c Zeit. physiol. Clicin.. 1010 (05), 78. 

 iiaBiochem. .lour., l!)l.'i (0), -.VM. 



