i'()h'M.['H(>.\ OF I inc Ar/n 023 



C\.II,N,0 + ILO >-C',n,X,(),, + XII3 



guanine ;;uaua!!K xantliiiiu 



or, hi case the guanine glueoside is present: 



C5HA-C,H4N„0 + H,0 >- CJIA - C,H3N A + ^ih 



suanosinc guanosinc-deaniinasc xanthosine 



lu the latter case a hydrolytic euzynie, xaiithosine-hydrolase, then 

 splits off the xanthine, so that by either route the end result is the 

 same. By a similar series of changes the adenine radical is converted 

 into hypoxanthine, either directly by adenase: 



C5H3N, + ILO >-Cjr,N,0 + XH3 



adenine aden;:se h\ poxanthine 



or by adenosine-deaminase the hypoxanthine-glucoside (inosine) is 

 formed, and later the hypoxanthine is split off. 



We now have hypoxanthine and xanthine, which, in the presence of 

 oxygen, are oxidized to form uric acid, thus : 



QH^N.O + O ^ >^C,H,N,Oo 



hypoxanthine hypoxanthine-oxidase xanthine 



CH^NA + O y C-,H,N,03 



xanthine xanthine-oxidase uric acid 



Further oxidation of the uric acid causes its conversion into the 

 much more soluble allantoin, thus : 



C5H,N,03 + + H,0— >-C,HeN,03 + CO^ 



uric acid uricase allantoin 



It is thus evident that the steps of the disintegration of nucleic acid 

 are numerous, but that each separate process is a simple one ; and also, 

 that it has been possible to follow out and distinguish the several steps 

 and to establish the fact that each step depends on a distinct and 

 specific enzyme. Not every tissue possesses all the enzymes of purine 

 destiniction, and in different species of animals the distribution of the 

 enzymes is different. For example, the enzyme xanthine-oxidase, 

 which oxidizes xanthine into uric acid, is found in man only in the 

 liver, and also in other animals it is of limited distribution, being 

 found usually only in the liver or in the liver and kidney, but in the 

 dog it seems to be present in several tissues. The deaminizing en- 

 zymes, adenase and guanase, are much more widely distributed, but by 

 no means universally. Adenase, for example, is not present in the 

 tissues of the rat, and not in the tissues of adult human beings.^ 

 Guanase is absent from the spleen and liver of the pig and from 

 human spleen, although present in most other tissues. Uricase, the 

 enzyme which destroys uric acid, also has peculiarities of distribution, 

 being seldom found in any other tissue than the liver or kidney, and 

 being absent entireh- from the tissues of man, and from the birds and 



8 There liave l)cen some rejiorts indicatiiisj tlie presence of adenase in fetal liuman 

 tissues (Long, Jour. Biol. Chem., 101.3 (la), 440). 



