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Bacterial metabolism of 5-aminosalicylic acid. Initial ring cleavage.

ABSTRACT: The metabolism of 5-aminosalicylate (5AS) by a bacterial strain, Pseudomonas sp. BN9, was studied. Intact cells of Pseudomonas sp. BN9 grown with 5AS oxidized 5AS and 2,5-dihydroxybenzoate (gentisate), whereas cells grown with gentisate oxidized only the growth substrate of all substituted salicylates tested. Cell extracts from Pseudomonas sp. BN9 catalysed the stoichiometric reaction of 1 mol of oxygen with 1 mol of 5AS to a metabolite with an intense u.v.-absorption maximum at 352 nm (pH 8.0). This metabolite was accumulated under neutral conditions, but was rapidly destroyed at acid pH. It was identified by m.s. and acid-catalysed deamination to fumarylpyruvate (trans-2,4-dioxohept-5-enedioic acid) as cis-4-amino-6-carboxy-2-oxohexa-3,5-dienoate, thus demonstrating direct cleavage of the monohydroxylated substrate 5AS to a non-aromatic ring-fission product. The enzyme responsible for conversion of 5AS was shown to be Fe(II)-dependent and to be distinct from gentisate 1,2-dioxygenase in strain BN9.

SUBMITTER: Stolz A

PROVIDER: S-EPMC1130840 | biostudies-other | 1992 Mar

REPOSITORIES: biostudies-other

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Project description:Chemical oxidation with hydroxyl radical (HO•) and sulfate radical (SO4•-) is often used to treat water contaminated with aromatic compounds. Although oxidation of aromatics by these radicals has been studied for decades, the commonly accepted transformation pathway-sequential hydroxylation of the ring followed by ring cleavage and mineralization of the resulting products-does not account for the loss of the parent compound observed during the initial phase of the process. To assess the importance of pathways for aromatic compound oxidation that do not result in ring hydroxylation, we identified products formed after the initial reaction between HO• or SO4•- and benzene, toluene, ethylbenzene, and (BTEX) xylene isomers. We quantified products of ring hydroxylation and oxidation of alkyl substituents as well as a suite of ring-cleavage products, including acetaldehyde, formic acid, 6-, 7-, or 8-carbon oxoenals and oxodials. Other ring-cleavage products, which were most likely aldehydes and organic acids, were observed but not quantified. When SO4•- was used as the oxidant, aromatic organosulfates also were formed. Our results indicated that the initial phase of the oxidation process involves radical addition, hydrogen abstraction, or one-electron transfer to the ring followed by reaction with O2. The hydroxycyclohexadienylperoxy radical produced in this reaction can eliminate hydroperoxyl radical (HO2•) to produce a phenolic compound or it can rearrange to form a bicyclic peroxy intermediate that subsequently undergoes ring cleavage. Hydroxylation of the ring and oxidation of the alkyl substituent accounted for approximately 15-40% of the reacted mass of the parent compound. Ring-cleavage products for which quantification was possible accounted for approximately 2 to 10% of the reacted mass. Our results raise concerns about the formation of toxic ring-cleavage products during the initial stage of oxidation whenever HO• or SO4•- is used for the treatment of water containing benzene or alkylbenzenes.

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Bacterial metabolism of 5-aminosalicylic acid. Initial ring cleavage.

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