Methanol, methanogenesis from

In contrast, disproportioning of methanol occurs with methanogenesis from methanol as given in Eq. 2. 

Fig. 1. The pathways of methanogenesis. Intermediates are abbreviated as in the text. The thick lines indicate the pathway for H2-CO2 methanogenesis, which is also in common to some extent with methanogenesis from one or more other substrates. The thin lines indicate specialized portions of pathways of methanogenesis from methanol, formate, and acetate, (a) Two different dehydrogenases have been reported, one dependent on H2F420, and one dependent on H2. (b) The source of these electrons may be H2F420 in some cases, but in other cases it is unknown see the text, (c) This is a possible alternative for methanol oxidation to the methylene-RjMPT level see the text for details.

Methanogenesis from methanol occurs by its disproportionation to methane and carbon dioxide (Reactions (5) and (5A), Table 2). Reducing equivalents derived from the oxidation of one methanol to CO2 are used to reduce three methanols to CH4. 

M. barkeri extracts methanogenesis from this labelled protein is at least 100 times faster than the non-enzymatic reaction between CoM and methylcobalamin they postulated that this protein acts as a methyltransferase in methanogenesis from methanol. Finally, Van der Meijden et al. [152-155] resolved the M. barkeri methyl transfer from methanol to CoM into two steps involving methyltransferase 1 and 2, or MTi and MT2. The oxygen-sensitive corrinoid protein MTj in its most reduced state (Co" ) accepts the methyl group from methanol [153,154] ... 

Lovley D. R. and Klug M. J. (1983a) Methanogenesis from methanol and methylamines and acetogenesis from hydrogen and carbon dioxide in the sediments of a eutrophic lake. Appl. Environ. Microbiol. 45, 1310-1315. 

The first evidence for cobalamin involvement in the conversion of methanol to methane was provided by Blaylock and Stadtman [196,216-218] with extracts of methanol-grown M. barkeri they demonstrated enzymatic formation of methylcobalamin from methanol, and subsequent reduction of methylcobalamin to methane. Later Blaylock [196] showed that conversion of methanol to methylcobalamin requires a heat-stable cofactor and at least three proteins, a 100-200 kDa Bi2-enzyme (methyltransferase), a ferredoxin, and an unidentified protein. Blaylock speculated that the role of hydrogen and ferredoxin in the conversion of methanol to methylcobalamin was in the reduction of the Bi2-protein. This work led to the proposal that methylcobalamin was the direct precursor of methane in methanogenesis from various substrates [196,218]. 

Methanogenesis from methylamines (Reaction 6, Table 2) follows almost the same route as methanol to CH4 and CO2 [227], although each system probably requires specific components for substrate transport, and to form a common methylated product. For example, extracts of M. barkeri grown on trimethylamine (TMA) produce methane from TMA + H2, but extracts from methanol- or dimethylamine-grown cells do not [227],... 

Fig. 12. Proposed role of methyl-tetrahydromethanopterin (CH3-H4MPT) coenzymeM (H-S-CoM) methyltransferase in methanogenesis from CO2, acetate and methanol methyltransferase as a reversible Na -translocating membrane protein. During CH4 formation from CO2 and from acetate, methyltransferase is involved in primary Na" extrusion generating A/INa during methanol disproportionation to CH4 and CO2 the enzyme is involved in A/iNa -driven methanol oxidation.

In contrast to Sec-tRNA and fMet-tRNA formation, Pyl-tRNA y formation can occur by direct acylation of pyrrolysine onto tRNA i Pyrrolysine (Pyl), the twenty-second amino acid, was discovered incorporated in methylamine methyltrans-ferases from Methanosarcinaceae, a branch of methanogenic archaea that has the ability to reduce a wide variety of compounds to methane including carbon dioxide, acetate, methanol, methylated thiols, and methylated amines (72). Methanogenesis... 

It was shown later that ATP synthesis can be coupled to methanogenesis at very low A/iH values (—90 to —lOOmV) [103] Proton potentials of defined magnitude, adjusted with K gradient in the presence of valinomycin, were applied to cells of Methanosarcina barkeri and Methanobacterium thermoautotrophicum, and the ATP pool and the rates of methane formation from Hz/methanol and from Hz/COz were followed as a function of... 

In marine sediments below the sulfate zone, methanogenesis is the predominant terminal pathway of organic carbon degradation. Methane may also be formed from acetate or from organic Cj-compounds such as methanol or methylamines ... 

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