BACTERIAL FERMENTATIONS 



The formation of glycine and formate from purines points 

 to a similarity between tlie mechanisms of the bacterial fermenta- 

 tion and the synthesis of purines in animals. This similarity has 

 been further defined by the use of tracer methods (15,26). 

 Nitrogen atoms in the 1, 3, and 9 positions of the purine have 

 been shown to be converted to ammonia, and the nitrogen in 

 position 7 appears in glycine. Carbon from positions 2 and 6 

 goes to carbon dioxide, from positions 4 and 5 to the carboxyl 

 and methylene carbons of glycine, and from position 8 to formate. 

 The only conspicuous difference between the fermentation and 

 synthetic processes with respect to the tracer data is in the fate or 

 source of the carbon in position 2. In the uric acid of the pigeon 

 this carbon atom is derived from formate, whereas in the 

 fermentation it is converted to carbon, dioxide by a path not 

 involving formate. This suggests that the purine which is actu- 

 ally degraded by the bacterial system, as contrasted with the 

 purine added as a substrate, is more oxidized in the 2 position 

 than is the hypoxanthine ribotide which appears to be the first 

 purine derivative synthesized from nonpurine precursors in 

 animals (7). 



Several types of evidence, which will not be given here, 

 indicate that uric acid, guanine, and hypoxanthine are converted 

 to xanthine before the purine ring structure is disrupted. The 

 decomposition of xanthine has been studied with crude cell-free 

 extracts (6,27,30), and has been shown to proceed in accordance 

 with the following equation 



1 xanthine + 6H2O > 



3 ammonia + 2 carbon dioxide + 1 formate + 1 glycine 



which represents a nonoxidative process. Unlike intact cells, 

 the cell-free extracts used in these experiments do not form 

 appreciable amounts of acetate. 



A question of special interest in xanthine decomposition is 

 the point of attack on the purine molecule. Previous studies on 

 purine synthesis in birds indicated that the ribotide of 4-amino- 

 5-carboxamidoimidazole combines with "formate" to yield a 



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