Purine Fermentation by Clostridium Cylindrosporum

Xanthine (I) is converted to carbon dioxide, formic acid, glycine, and ammonia by crude extracts of Clostridium acidi-urici (1) and Clostridium cylindrosporum (2). Conditions under which an intermediate in this process is accumulated in incubation mixtures of xanthine and the crude extract were described in Paper III of this series (3). The compound was identified as 4-amino-5-imidazolecarboxylic acid (III), and its enzymatic decarboxylation to 4-aminoimidazole (IV) by extracts of 6. cylindrosporum was also demonstrated. The close relation of these compounds to 4-amino-5-imidazolecarboxamide is evident and suggested that this purine fermentation parallels the pathway of purine biosynthesis (4) involving the free bases rather than ribotides. However, 4-amino-5-imidazolecarboxamide is not degraded by extracts of the organism which convert xanthine to 4-amino-5-imidazolecarboxylic acid. Another intermediate in the degradative path which was found to accumulate when extracts were incubated with xanthine in the presence of sequestering agents is described in this paper. The isolation and characterization of this compound as 4-ureido-5-imidazolecarboxylic acid (II) provide additional evidence regarding the general scheme of purine degradation in C. cylindrosporum. This scheme, based on the observation presented here and in previous papers of the series (2, 3), is represented in the accompanying diagram.