H. A. BARKER 



hyde and the butyryl-CoA-crotonyl-CoA system (21) appears 

 to be of the order of 0.2 v., which is more than enough to permit 

 the formation of one high-energy phosphate bond from ortho- 

 phosphate. Such a coenzyme-hnked phosphorylation could 

 account for the importance of butyrate and caproate synthesis 

 in the metabolism of C. kluyveri. However, as yet there is no 

 evidence for such a mechanism. In fact, it has not been possible 

 to observe a reduction of crotonyl compounds by reduced DPN 

 and TPN, which are formed in the oxidation of ethanol and 

 acetaldehyde. 



Purine Fermentations 



The fermentation of purines by C. acidi-urici and C. cylindro- 

 sporum presents some interesting and as yet partially unsolved 

 biochemical problems. 



The main products of the fermentation of uric acid, xan- 

 thine, or guanine are ammonia, carbon dioxide, and acetate, 

 sometimes accompanied by small amounts of formate and 

 glycine (2,27) . Early experiments with cell suspensions indicated 

 that the mechanism of the purine fermentation is quite different 

 from that of uric acid oxidation via allantoin in animals and 

 aerobic bacteria. This conclusion was based in part on the 

 observation that neither allantoin nor urea is decomposed under 

 conditions in which uric acid is rapidly fermented. 



The first definite indication of the path of uric acid break- 

 down was the discovery that glycine is formed in appreciable 

 amounts and is also decomposed when uric acid is simultaneously 

 available to the organism (2). The dependence of glycine 

 decomposition on the presence of uric acid suggested some sort 

 of interaction between the two substances. This was further 

 supported by the observation that certain cell suspensions of C 

 acidi-urici exhibit a conspicuous lag in uric acid decomposition, 

 which can be eliminated completely by the addition of glycine. 

 Later work (30) suggests that the oxidation of glycine is coupled 

 with a reduction of uric acid to xanthine. 



82 



