Thermodynamics of partial reactions

Thermodynamics of partial reactions. On the basis of thermodynamic data (Table 2) the energetics of the reduction of CO2 to CH4 can be divided into three parts, the energy coupling of which can be tested experimentally with cell suspensions the reduction of CO2 to methylene-H4MPT (CH2=H4MPT, formaldehyde level), the conversion of methylene-H4MPT to methyl-coenzyme M (CH3-S-C0M, methanol level), and the reduction of CH3-S-C0M to CH4 (Fig. 4). 

The energetics of the endergonic part of the pathway, the reduction of CO2 to methylene-H4MPT, has been studied by analyzing the reverse reaction, the exergonic conversion of formaldehyde to CO2 and Hz.  

Methanogens catalyze this reaction if methanogenesis was blocked by inhibitors of the CH3-S-C0M reductase [105,106], 

Methyl-coenzyme Mi reduction to CH4 - site of primary AphT generation and of ATP synthesis 

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 

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