Fig. 2: Metabolic thermodynamic model of the anaerobic oxidation of butane (AOB) and reverse AOB.

A Refined central carbon and energy metabolism during AOB (black arrows) or reverse AOB (light blue arrows). Numbers in the figure correspond to reactions in Table 1. B The reducing equivalents released during AOB/consumed during rAOB include 2 XH₂, 5 NADH, 4 F₄₂₀H₂, and 4 Fd_red, which in total account for 26 electrons. C, D Quasi-equilibrium concentrations (mol L⁻¹) of AOB/rAOB metabolites considering a standard redox potential of XH₂/X of −0.220 V. C The AOB model considers energy recovery at F₄₂₀H₂ and Fd_red oxidation, energy investment at the butyl-CoM/butyryl-CoA conversion and at electron transport between MQ and X, and energy dissipation (∆G_dis) at oxidation of methylene-tetrahydromethanopterin. Metabolite concentrations were calculated under XH₂/X ratios of 2, 4, and 8, corresponding to AOB free energy change (∆G_cat) of −147.23, −124.91, and −102.58 kJ mol⁻¹ butane, respectively. D The rAOB model considers a switch in energy recovery and energy investment, with energy dissipation occurring at acetyl-CoA synthesis. Metabolite concentrations were calculated for XH₂/X ratios of 1000, 2000, 4000, and 8000, corresponding to rAOB ∆G_cat of −66.54, −88.87, −111.19, and −133.52 kJ mol⁻¹ butane, respectively. Δµ_H+ denotes the free energy required to translocate one proton across the membrane (−20 kJ mol⁻¹). Source data are provided as a Source Data file.