PURINES 173 



acid and purines are administered to the intact animal, 

 when these -substances are digested with various tissue 

 extracts, and when tissues are allowed to undergo autolysis. 

 Using these methods, the conversion of nucleic acid into 

 uric acid has been ascribed to a series of enzymes. The 

 change occurs in the following stages : — 



1. By a series of ferments termed nucleases, the tetra- 

 nucleotide is split into mononucleotides, from which are 

 hberated adenine and guanine either directly or through 

 the intermediate formation of nucleosides. 



2. Deaminising ferments, adenase and guanase, convert 

 respectively adenine into hypoxanthine and guanine into 

 xanthine. 



3. The ferment xanthoxidase oxidises hypoxanthine to 

 xanthine and xanthine to uric acid. 



These changes may be thus set forth : — 



' Tetranucleotide (nucleic acid) 



^ . 

 Mononucleotide (phosphoric a cid + hexose + base) 



By 

 nucleases > 



> Nucleoside (hexose + base) 



V Adenine Guanine 



(by I I (by 



adenase) I I guanase) 



Hypoxanthine -> Xanthine -> Uric acid 



(by Xanthoxidase) 



It is not to be imagined that all these ferments exist 

 in every tissue. Indeed, their distribution appears to bo 

 hmited to a few organs, such as the hver, pancreas and 

 spleen, and even in these they are not all present. Wide 



