BACTERIAL FERMENTATIONS 



In support of this scheme Beck showed that cells grown 

 on guanine contain an active guanase capable of converting 

 guanine to xanthine. 60 He also found that the decomposi- 

 tion of uric acid by cells grown on this purine is inhibited 

 by 2,4-dinitrophenol without affecting the fermentation of 

 xanthine. Radin and Barker, 61 using both dried-cell prep- 

 arations and cell-free extracts of CI. acidi-urici, further 

 showed that, whereas the decomposition of uric acid was 

 increased by the presence of reducing agents and inhibited 

 by oxidizing agents, the decomposition of xanthine was 

 almost independent of such reagents. These and other 

 types of evidence support the above scheme. 



The study of the enzymatic steps in the decomposition of 

 xanthine was initiated by Radin and Barker 61 and inde- 

 pendently by Bradshaw and Beck. 62 Both groups found 

 that crude cell-free extracts readily convert xanthine to 

 ammonia, carbon dioxide, formate, and glycine, or products 

 which yield these substances in the analytical procedures 

 used. Radin also made the important observation that one 

 or more compounds which react in the Pauly and Bratton- 

 Marshall tests were formed from xanthine in small amounts. 

 The nature of the tests indicated that they were probably 

 aminoimidazoles. These observations suggested that the 

 pyrimidine ring of xanthine was first attacked in such a 

 way as to form an imidazole derivative which was then 

 further degraded. 



The individual enzymatic steps in the conversion of xan- 

 thine to glycine have been extensively studied by Rabino- 

 witz and his collaborators, who have developed methods 

 for the isolation, analysis, and characterization of three 

 imidazole derivatives and have clarified the reactions in- 

 volved in the tetrahydrofolic acid dependent formation of 

 glycine and formate. 



The decomposition of xanthine occurs by a hydrolytic 



