FERMENTATIONS OF NITROGENOUS COMPOUNDS |H 



dioxide have confirmed the conclusion, already reached by 

 other methods, that these compounds are not stable end 

 products but are extensively further metabolized. 53 ' 58 The 

 carboxyl carbon of glycine is converted mainly to carbon 

 dioxide, whereas the methylene carbon is extensively incor- 

 porated into both carbons of acetate. Formate is partly 

 oxidized to carbon dioxide and partly incorporated into 

 the methyl group of acetate. Finally, carbon dioxide is 

 rapidly reduced to formate and is extensively incorporated 

 into the carboxyl group of glycine and into both carbon 

 atoms of acetate. Acetate itself is not metabolized to a sig- 

 nificant extent. In addition to establishing the roles of 

 carbon dioxide, formate, and glycine as intermediates, 

 these observations also emphasize the complexity of the 

 fermentation. 



I have already mentioned that xanthine is the purine 

 which probably undergoes ring cleavage in the purine fer- 

 mentation. The evidence for this, which is now fairly 

 conclusive, was obtained in several ways. The first definite 

 indication for the key role of xanthine was obtained by 

 Beck 59 in experiments on the influence of the growth sub- 

 strate on the relative rates of decomposition of xanthine, 

 guanine, uric acid, and hypoxanthine. He found that uric 

 acid, hypoxanthine, and to a lesser extent guanine are de- 

 composed by adaptive enzyme systems, whereas xanthine 

 is rapidly utilized by cells grown on any of the four purines. 

 This suggested that uric acid, guanine, and hypoxanthine 

 are broken down via xanthine as follows: 



Guanine ., 



■NH 3 



Hypoxanthine ~ 2 > Xanthine < 2H Uric acid 



i- 



i 



End products 



