Metabolic Activation of the Potent Mutagen, 2-Naphthohydroxamic Acid, in Salmonella typhimurium TA981

The objective of the present study was to explore the mechanisms responsible for the strong, direct-acting mutagenicity of 2-naphthohydroxamic acid (NHA) for Salmonella typhimurium TA98. NHA was converted to its O-acetate (O-Ac-NHA) by acetyl-CoA, in the presence of competent or heat-treated cell-free bacterial preparations. O-Ac-NHA, which is more mutagenic than NHA, reacted nonenzymatically with tRNA in neutral solutions with retention of both the naphthyl and carbonyl groups in the products, but NHA did not react. Enzymatic sulfate conjugation was not demonstrated. TA98 cells converted NHA to 2-aminonaphthalene, presumably through a Lossen rearrangement fol lowing 0-acetylation or conjugation by other metabolic pathways. TA98 cells reduced O-Ac-NHA to 2-naphthamide, and NADH and NADPH were shown to be cofactors for reduction in the presence of a cell-free bacterial preparation. Although horseradish peroxidase and Ilo, cata lyzed the binding of these compounds to tRNA, no evidence of oxidation of NHA or O-Ac-NHA was obtained with H2O2 and cell-free prepara tions of TA98 or the cells themselves, as judged by the lack of formation of the peroxidative product, 2-naphthoic acid. Both NHA and O-AcNHA reacted with DNA of TA98 with retention of both naphthyl group and carbonyl of the naphthoyl moiety in the adduct(s). These results suggest that NHA may be activated in TA98 by esterification, and the resulting metabolites may amidate or carbamoylate nucleic acids.