Studies on the accumulation of 4-amino-5-imidazole carboxamide in Escherichia coli.

When cultures of Escherichia coli are partially inhibited by sulfonamides they accumulate a diazotizable and nonacetylable amine in the medium (Fox, 1942). The amine was isolated by Stetten and Fox (1945) and characterized by Shive et al. (1947) as 4-amino-5-imidazole carboxamide. The latter authors suggested that the amine was a precursor of purines as it only required the addition of a one carbon fragment for completion of the purine skeleton. Its transformation to purines is mediated by p-aminobenzoic acid (PABA) and sulfonamides interfere in this conversion. The nature of this amine for purine synthesisin E. coli has since been amply confirmed. Some purine requiring mutants of this organism accumulate it (Gots, 1950). Ben-Ishai et al. (1951) have reported that certain other purine auxotrophs of E. coli can utilize the amine for growth, though higher concentrations of it are needed. Woolley and Pringle (1950) observed that the amine accumulated during growth inhibition of E. coli by aminopterin, suggesting that PABA acted through folic acid (FA) in the conversion of the amine to purine. The implication of FA in purine synthesis has been suggested by other lines of investigation. Purines have been shown to be active in decreasing or replacing the FA requirement for growth (Mitchell and Snell, 1941; Snell and Mitchell, 1941; Stokstad, 1941; Stokes, 1944; Krueger and Peterson, 1945) and in overcoming growth inhibition of a variety of microorganisms caused by FA analogue antagonists (Rogers and Shive, 1948). Vitamin B12 has also been implicated in purine biosynthesis. Shive (1950) has shown that in the presence of vitamin B12 high concentrations of sulfanilamide are required to inhibit the synthesis of purines. Purine auxotrophs of E. coli utilize the amine for growth better in the presence of vitamin B12 (Ben-Ishae et al., 1951). The involvement of vitamin B12 and FA in purine synthesis discussed above suggested a study of the effects of pteroylglutamic acid (PGA), leucovorin (5-formyl, 5-6-7-8-tetrahydrofolic acid; LV) and vitamin B12 on amine accumulation under cultural conditions of restricted growth in E. coli. Methionine has also been included in the experiments for a study of its effects in view of the replaceability (Davis and Mingioli, 1950) of methionine and B12 for growth of certain induced mutants of E. coli.