298 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



The Biological Relationship of the Purines. 



Adenine and guanine are constituents of the nucleic acid of 

 animals and plants. Whilst still in combination in the molecule of 

 nucleic acid they may be acted upon by enzymes in the tissues and 

 converted respectively into hypoxanthine and xanthine. Nucleic acid 

 on decomposition in the tissues will yield adenine and guanine, or 

 hypoxanthine and xanthine. Adenine and guanine are acted upon 

 by the enzymes, adenase and guanase, in the tissues and converted 

 into hypoxanthine and xanthine. These enzymes are present in 

 most organs, but not in all organs ; sometimes an organ contains 

 both enzymes, sometimes only one enzyme, sometimes neither 

 enzyme. Hypoxanthine is oxidised by the tissues to xanthine and 

 xanthine is oxidised to uric acid (xanthine oxidase). In some 

 animals, but not in man, uric acid is oxidised to allantoine (uricase). 

 The changes may be brief y represented as follows : 



Nucleic acid 

 i 



adenine 

 hypoxanthine *- xanthine >. uric acid 



allantoine 



The mechanism of these transformations has been difficult to eluci- 

 date and much confusion as to the origin of uric acid has existed. 

 A full account of the work is given in W. Jones' monograph on 

 " Nucleic Acids ". 



