Oxidation of carbon compounds by Methylococcus capsulatus

The effect of various potential Inhibitors on methane oxidation was tested on whole-cell suspensions of Methylococcus capsulatus (strain Texas) (TRMC ) and Methylococcus capsulatus (strain Bath) (MC). Methane oxidation by TRMC was specifically inhibited by a large number of metal-chelating/binding agents and suggested the involvement of a metal ion(s) with the methane mono -oxygenase.\ud \ud The whole-cell results of MC showed a much more restricted specific inhibitor pattern for methane oxidation, which was confirmed by cell-free studies. The inhibitor pattern of MC was compared with that of TRMC and with reported patterns for other methane-utilisers. The effect of a number of acetylenic compounds on methane oxidation by MC was tested and the results discussed.\ud \ud The substrate specificity of the methane mono-oxygenase from MC was determined and found to be very non-specific. It catalysed the oxidation of various substituted methane derivatives, including methanol. C₁ -C₈ n-alkanes were hydroxylated to the corresponding 1- and 2-alcohols, carbon monoxide to carbon dioxide, terminal alkenes to the corresponding 1, 2-epoxides and internal alkenes to a variety of products. Ethers, alicyclic, aromatic and heterocyclic compounds were also oxidised. The significance of the various oxidations are discussed. Only NADPH could replace NADH as electron donor for methane mono-oxygenase activity.\ud \ud The subject of non-growth substrate oxidation by micro-organisms is discussed and the terminology of the area critically reviewed. Whole-cell oxidation studies with MC revealed five fortuitously oxidised non-growth substrates (chloromethane, bromomethane, dimethyl ether, ethene and propene) and seven cometabolic non-growth substrates (carbon monoxide, diethyl ether, ethane, propane, but-1 -ene, cis but-2-ene and trans but-2-ene). From these, dimethyl ether, bromomethane and carbon monoxide were selected to study in detail their effect on cellular metabolism of MC.\ud \ud During the oxidation studies it was suspected that an NAD(P)⁺ -linked aldehyde dehydrogenase was present. Confirmative tests proved positive. Activity in crude cell-free extracts was lost on dialysis, but could be restored by supplementing with inactive, heat-treated extract. The non-dialysable, heat-sensitive component was isolated and purified. The heat-stable component/co-factor was presumed to be a low molecular weight protein or polypeptide.\ud \ud The enzymic potential for an NAD(P)⁺ -linked cyclic scheme for the complete oxidation of formaldehyde was detected in crude cell- free extracts of MC. The relative Importance of the different formaldehyde oxidation systems found is discussed.\ud