A C-13-NMR STUDY OF THE MECHANISM OF BACTERIAL METABOLISM OF MONOMETHYL SULFATE

Two different mechanisms have been proposed previously for initiating the biodegradation of monomethyl sulfate (MeSO(4)) in bacteria, For a Hyphomicrobium species, a sulfatase enzyme has been proposed to hydrol yse MeSO(4) to methanol and inorganic sulfate. For an Agrobacterium sp ., an alternative proposal involves monooxygenation of MeSO(4) (hydrox ylation) to produce methanediol monosulfate, which decomposes spontane ously to formaldehyde and inorganic sulfate. In the present study, C-1 3-NMR was used to monitor metabolic intermediates of [C-13]MeSO(4) in real time in each species in order to resolve the issue of mechanism o f biodegradation. Agrobacterium sp. M3C grew on MeSO(4) but not on met hanol. MeSO(4)-grown cells catabolised [C-13]MeSO(4) but not [C-13]met hanol, and [C-13]methanol did not accumulate from MeSO(4) in the prese nce of a known inhibitor of methanol dehydrogenase (cyclopropanol). Hy phomicrobium MS223 grew on MeSO(4) and, in contrast with the Agrobacte rium sp., also on methanol. The normally rapid metabolism of [C-13]met hanol by methanol-grown cells was arrested by cyclopropanol, but metab olism of [C-13]MeSO(4) by MeSO(4)-grown cells was unaffected. Moreover there was no accumulation of [C-13]methanol from [C-13]MeSO(4) under conditions in which methanol dehydrogenase was shown to be inactive. T he results provided strong evidence against the intermediacy of methan ol in the biodegradation of MeSO(4) in either species, and thereby ren der untenable mechanisms involving sulfatase-mediated hydrolysis of Me SO(4). The data are consistent with the hydroxylation of MeSO(4) via a monooxygenation mechanism and subsequent spontaneous hydrolysis of th e methanediol monosulfate intermediate.