NUCLEIN OR PURINE METABOLISM 



821 



This was one of the earliest facts discovered in the metabolism of purines. 

 Horbaczewski showed that, if spleen pulp be digested with blood for some time, it is 

 possible to extract a considerable amount of xanthine from the mixture. If however 

 oxygen be bubbled through the fluid, the xanthine disappears, its place being taken 

 by uric acid. 



From the more complex nucleic acids the amino-purines, adenine and 

 guanine, are set free. These first undergo deamination under the action 

 of special ferments, adenase and guanase, and are thus converted into 

 hypoxanthine and xanthine respectively. These bodies subsequently, 

 under the action of oxidases, may be converted into uric acid. 



All these changes occur in the living body, though not necessarily in the order just 

 set out. Thus when the pyrimidine derivatives are administered to dogs, they pass 

 out unchanged. If however free nucleic acid be administered to the animal, no trace 

 of these derivatives can be found in the urine, so that they must have undergone com- 

 plete oxidation. In the same way the dog's liver is able to deaminise completely 

 the adenine group of nucleic acid, converting it into hypoxanthine, but is without 

 effect on free adenine. It is evident therefore that the various ferments which have 

 been described act partly on the whole nucleoside molecule, partly on the products 

 of its decomposition, and that the results of the action of the body ferments are not 

 the same in the two cases. 



If we make this reservation, namely, that the constituent parts of the nucleic acid 

 molecule may undergo changes while still bound to the other parts, we may represent 

 diagrammatically the formation of uric acid from nucleic acid as follows : 



Ferments 

 Nuclease 



Nucleic acid 



Phosphoric acid Guanosine Adenosine Uiidine Cytidine 



Deaminase Xanthosine Inosine 



Hydrolysis 



Oxidase 



Fate unknown 



Xanthine Hypoxanthine 

 Xanthine 



Oxidase 



Oxidase . 

 (Uricase) 



or 

 Nuclease 



_l 



Purine nuclease 



Pentose-phosphoric acid Guanine 

 Deaminase 

 (Guanase and adenase) 



Uric acid 



I 



Allantoin (in dogs) 

 Nucleic acid 



I 



4 Mononucleotides 



Oxidase 

 Oxidase 



Adenine Pyrimidine bases 

 Xanthine Hypoxanthine 

 Xanthine 





Uric acid 



