STUDIES ON PURINE METABOLISM IN BACTERIA I

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Abstract
That p-aminobenzoic acid (PABA) functions in the synthesis of 4-amino-5-imidazolecarboxamide (AICA) was shown by (1) the accumulation of AICA by a PABA requiring mutant of Escherichia coli and (2) the accumulation of AICA under conditions of inhibition of E. coli by such analogues of PABA as atoxyl, p-aminoacetophone and p-aminosalicylic acid. Compounds structurally related to PABA whose inhibition could not be competitively antagonized by PABA were inactive with respect to AICA accumulation. Methionine and B12, both capable of sparing the PABA requirement of the mutant, depressed the accumulation of AICA but were not completely equivalent in this action. The ability of methionine to relieve AICA accumulation depended on the PABA concn. Methionine may be a necessary factor in the conversion of AICA to purine, probably through its action as a C donor. PABA through its derived co-enzyme mediates this reaction. Formate and other known C donors were inactive.