Mechanism of Lithoautotrophic Methane Formation Respiration but Not Fermentation

1 Mechanism of Lithoautotrophic Methane Formation Respiration but Not Fermentation 

Although a series of the reactions in the methane formation do not make a cycle as for compounds, as the formation of methane stimulates the reaction of carbon dioxide with methanofuran a series of the reactions seem to make a cycle in a sense of function. So the series of the reactions is called the Q cycle (Fig. 6.5). 

Among the reactions in the C cycle mentioned above, those that liberate enough free energy to form ATP are those catalyzed by methyl CoM reductase [reaction (6.2)] and H2 heterodisulfide oxidoreductase [reaction (6.3)] (Heiden et al., 1993). In the cycle, no organophosphate compounds are found, which can be the intermediate for ATP biosynthesis as observed in the fermentation. 

CH3SC0M + HSCoB Me lc°MRete CH4 + C0MS-SC0B +10.7 kcal (6.2) 

C0MS-SC0B + H2 H2 heterodisulfide oxidoreductase— HSCoM + HSCoB + 9.5 kcal (6.3) 

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