FERMENTATIONS OF NITROGENOUS COMPOUNDS 77 



nature of the observed fermentation products that aspartic 

 acid is converted either to fumarate or oxalacetate which is 

 then partly oxidized to acetate and carbon dioxide, and 

 partly reduced to succinate. The energy-yielding steps 

 could be the decomposition of the ureido group and the 

 oxidation of pyruvate; however, no phosphorylation reac- 

 tions have yet been demonstrated in this organism. 



Both the reduction of orotic acid and the conversion of 

 the latter to ureidosuccinic acid are readily reversible reac- 

 tions and therefore permit the synthesis of the pyrimidine 

 orotic acid from non-pyrimidine precursors. Considerable 

 evidence now indicates that this reaction sequence repre- 

 sents a major path of pyrimidine synthesis in living 

 organisms. 51 



Purine Fermentations by Clostridia. Clostridium 

 acidi-urici and CI. cylindrosporum readily ferment xan- 

 thine, uric acid, guanine, and 6,8-dihydroxypurine, and 

 decompose hypoxanthine, guanosine, and inosine more 

 slowly or after a period of adaptation. 52 Chemical studies 

 of purine fermentations by growing cultures have estab- 

 lished that the main products formed by CI. acidi-urici are 

 ammonia, carbon dioxide, and acetate; in addition a small 



N=COH 



I I 

 HOC C N 



\ 



CH+6H2O — ►■ 



/ 

 N— C— NH 



4NH 3 +3CQ 2 +lCH 3 COOH (11) 



amount of formate accumulates. If, as a first approxima- 

 tion, we disregard the formate, the decomposition of xan- 

 thine is represented by equation 11. With uric acid, the 

 yield of carbon dioxide is increased and the yield of acetate 



