# Formylmethanofuran dehydrogenase
**Formylmethanofuran dehydrogenase** is a molybdenum- or tungsten-containing enzyme complex of methanogenic archaea that catalyzes the reductive fixation of carbon dioxide onto the one-carbon carrier methanofuran (MFR), forming formyl-methanofuran, according to the equation CO₂ + MFR + 2[H] ⇌ CHO-MFR + H₂O under anoxic conditions[1](https://onlinelibrary.wiley.com/doi/10.1002/9781119951438.eibc2621). It performs the first step of the methanogenesis pathway from CO₂ and H₂ and is one of the few known enzymes, together with formate dehydrogenase and CO dehydrogenase, that directly reduce CO₂[2](https://pubs.acs.org/doi/10.1021/acs.chemrev.2c00581).
| Key fact | Detail |
|---|---|
| Reaction | CO₂ + MFR + 2[H] ⇌ CHO-MFR + H₂O, reversible, under anoxic conditions[1](https://onlinelibrary.wiley.com/doi/10.1002/9781119951438.eibc2621) |
| Isoenzymes | Fmd (molybdenum-dependent) and Fwd (tungsten-dependent)[1](https://onlinelibrary.wiley.com/doi/10.1002/9781119951438.eibc2621) |
| Architecture | Fwd from *Methanothermobacter wolfei* is a (FwdABCDFG)₄ tetramer of 24 subunits with 46 [4Fe–4S] clusters supporting electron transfer to the tungsten CO₂-reducing module (FwdB), while the di-zinc condensation module (FwdA) catalyzes non-redox condensation[3](https://pubs.acs.org/chreay/article/126/14/8034/5168303/Semiartificial-CO2-Fixation-Using-Metal-Dependent) |
| Active carbon species | CO₂, not bicarbonate, as shown for the *Methanosarcina barkeri* enzyme[4](https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1432-1033.1997.00919.x) |
| Energetics | ΔG°′ for formyl-methanofuran formation from CO₂ and H₂ is +16 kJ/mol[5](https://academic.oup.com/femsre/article/23/1/13/575607) |
| Electron donor | Reduced ferredoxin[3](https://pubs.acs.org/chreay/article/126/14/8034/5168303/Semiartificial-CO2-Fixation-Using-Metal-Dependent) |
| First structure | Tungsten-dependent Fwd complex from *M. wolfei*, solved by Tristan Wagner, Ulrich Ermler, and Seigo Shima (Science, 2016)[1](https://onlinelibrary.wiley.com/doi/10.1002/9781119951438.eibc2621) |
## Role in methanogenesis
Methanogenic archaea produce methane from CO₂ and H₂, acetate, or C₁ compounds such as methanol in an energy-gaining process[6](https://www.sciencedirect.com/science/article/abs/pii/S1389172302802328). In the hydrogenotrophic pathway, reduction of CO₂ to formyl-methanofuran is the entry step, and the entire energy metabolism of these organisms relies on this CO₂ capture[7](https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.00486/full). The formyl group is then transferred to tetrahydromethanopterin by formylmethanofuran:tetrahydromethanopterin formyltransferase and carried through consecutive pterin intermediates to the methyl level[5](https://academic.oup.com/femsre/article/23/1/13/575607).
The reaction is endergonic under standard conditions (ΔG°′ = +16 kJ/mol) and becomes more positive at the low H₂ partial pressures found in the environment, so it is proposed that a sodium or proton gradient generated elsewhere in the pathway drives it[5](https://academic.oup.com/femsre/article/23/1/13/575607). In cytochrome-lacking hydrogenotrophic methanogens such as *Methanobrevibacter*, a cytoplasmic complex of heterodisulfide reductase (HdrABC), the non-F₄₂₀-reducing hydrogenase (MvhADG), and formylmethanofuran dehydrogenase (FmdABCDFG or FwdABCDFG) bifurcates electrons from H₂, providing low-potential electrons for formyl-MFR synthesis from CO₂ at a redox potential near −500 mV[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC10658910/).
## Two catalytic modules in one complex
The enzyme combines two chemically distinct reactions in a single protein complex. A formate-dehydrogenase unit containing a bis-pyranopterin guanosine dinucleotide-coordinated Mo or W center reduces CO₂ to formate, and an amidohydrolase unit with a dinuclear Zn²⁺ center condenses that formate with methanofuran[1](https://onlinelibrary.wiley.com/doi/10.1002/9781119951438.eibc2621). Because the methanofuran-binding site lies far from the tungsten center, formate must diffuse through an intraprotein tunnel from the site of CO₂ reduction to the di-zinc site where condensation occurs[9](https://www.jbc.org/article/S0021925820339223/pdf). In many family members, associated (poly)ferredoxin domains carrying iron–sulfur clusters supply electrons to the Mo/W redox module rather than to the non-redox di-zinc condensation module[1](https://onlinelibrary.wiley.com/doi/10.1002/9781119951438.eibc2621) • [17](https://www.nature.com/articles/s41467-024-53338-7).
The tungsten-dependent Fwd complex from *M. wolfei* is built as a tetramer of heterohexameric FwdABCDFG units, 24 subunits in total, with 46 [4Fe–4S] clusters electronically coupling the tungsten redox module responsible for CO₂ reduction: FwdB is a cysteine-ligated tungsten formate-dehydrogenase subunit, while the non-redox di-zinc condensation with the methanofuran cofactor occurs at FwdA, an amidohydrolase subunit harboring the binuclear Zn²⁺ center[3](https://pubs.acs.org/chreay/article/126/14/8034/5168303/Semiartificial-CO2-Fixation-Using-Metal-Dependent). The reaction had been puzzling for decades; earlier mechanisms invoked a carboxy-MFR intermediate that was never detected, and the overall picture became clearer only with the 2016 crystal structure[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC11656701/).
## Isoenzymes and metal choice
Two major variants exist in methanogens, distinguished by the metal in the active site: the tungsten-containing Fwd and the molybdenum-containing Fmd, and multiple paralogs of both occur in organisms such as *Methanosarcina acetivorans*[11](https://journals.plos.org/plosbiology/article?id=10.1371%2Fjournal.pbio.3001508). The *M. barkeri* molybdenum enzyme contains five distinct subunits encoded in the transcription unit fmdEFACDB, uses molybdopterin guanine dinucleotide, and carries 30 nonheme iron atoms and 30 acid-labile sulfide; its FmdB subunit, which resembles bacterial formate dehydrogenase, is considered the catalytic subunit[5](https://academic.oup.com/femsre/article/23/1/13/575607). The tungsten enzyme of *Methanobacterium thermoautotrophicum* has four subunits (FwdABCD) cotranscribed with three further genes (fwdHFGDACB)[5](https://academic.oup.com/femsre/article/23/1/13/575607).
Metal use tracks ecology. Some methanogens express tungsten-containing Fwd in place of molybdenum forms[12](https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2012.00061/full), and the hyperthermophiles *Methanopyrus kandleri* and *Methanococcus jannaschii* encode only tungsten isoenzymes, consistent with the exclusive use of tungsten in enzymes from hyperthermophilic microbes; *M. kandleri* carries two tungsten isozymes, one a novel selenoenzyme[5](https://academic.oup.com/femsre/article/23/1/13/575607).
## Substrate specificity and the active CO₂ species
The molybdenum enzyme from *M. barkeri* is fairly specific. With the activity on N-formylmethanofuran set at 100%, it dehydrogenates N-furfurylformamide at 11%, N-methylformamide at 0.2%, formamide at 0.1%, and formate at 1% of that rate[13](https://pubmed.ncbi.nlm.nih.gov/8125106/). With the same enzyme, CO₂ rather than bicarbonate was shown to be the active species of "CO₂" used by the dehydrogenase[4](https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1432-1033.1997.00919.x), and the enzyme catalyzes a methanofuran-dependent exchange between CO₂ and the formyl group of formyl-MF, consistent with N-carboxymethanofuran as an intermediate[5](https://academic.oup.com/femsre/article/23/1/13/575607).
## Distribution and evolution
Formylmethanofuran dehydrogenases belong to the formate dehydrogenase family of tungsten enzymes and the closely related DMSO reductase family of molybdenum enzymes, which share fundamentally the same active-site metal centers coordinated by two pyranopterin cofactors[14](https://pmc.ncbi.nlm.nih.gov/articles/PMC6295890/). The molybdenum- and tungsten-containing formate dehydrogenases and formylmethanofuran dehydrogenases are considered evolutionarily ancient, and both the acetogenic and methanogenic versions of the [Wood–Ljungdahl pathway](https://www.edgepedia.org/wood-ljungdahl-pathway) begin with CO₂ reduction by a Mo- or W-containing enzyme[14](https://pmc.ncbi.nlm.nih.gov/articles/PMC6295890/). The Mo/W-binding subunits FmdB and FwdB of methanogens are related to formate dehydrogenase of acetogens, while the remaining methyl-synthesis enzymes of the two groups are unrelated[15](https://pmc.ncbi.nlm.nih.gov/articles/PMC3685469/).
The enzyme also runs in reverse in anaerobic methane-oxidizing archaea (ANME), which oxidize methane and must fix the resulting CO₂. Based on homology to *M. acetivorans*, ANME largely contain the Fwd version, detected in proteomic analyses of methane seeps; some ANME-2 lineages also carry the Fmd version, and in ANME-2c the two gene sets occur together in a single large cluster, while the FwdFG subunits are absent from all ANME-1 genomes[11](https://journals.plos.org/plosbiology/article?id=10.1371%2Fjournal.pbio.3001508).
## Biotechnological interest
Because the enzyme captures CO₂ as a bound formyl group in an ATP-independent reaction, it is a target for electroenzymatic CO₂ fixation[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC11656701/). Molybdenum-dependent formylmethanofuran dehydrogenase has been used for bioelectrocatalytic CO₂ reduction, and its properties make it a template for protein engineering aimed at converting the greenhouse gas into formate, a stable, transportable storage medium for renewable energy and a precursor for chemical production[16](https://onlinelibrary.wiley.com/doi/full/10.1002/anie.202311981).
## References
1. [Wagner T., Ermler U., Shima S. Formyl-Methanofuran Dehydrogenase. Encyclopedia of Inorganic and Bioinorganic Chemistry (2018)](https://onlinelibrary.wiley.com/doi/10.1002/9781119951438.eibc2621)
2. [Enzymatic Conversion of CO2: From Natural to Artificial Utilization. Chemical Reviews (2022)](https://pubs.acs.org/doi/10.1021/acs.chemrev.2c00581)
3. [Semiartificial CO2 Fixation Using Metal-Dependent Formate Dehydrogenase. Chemical Reviews (2026)](https://pubs.acs.org/chreay/article/126/14/8034/5168303/Semiartificial-CO2-Fixation-Using-Metal-Dependent)
4. [Vorholt J.A. et al. The Active Species of 'CO2' Utilized by Formylmethanofuran Dehydrogenase from Methanogenic Archaea. European Journal of Biochemistry (1997)](https://febs.onlinelibrary.wiley.com/doi/10.1111/j.1432-1033.1997.00919.x)
5. [Ferry J.G. Enzymology of one-carbon metabolism in methanogenic pathways. FEMS Microbiology Reviews (1999)](https://academic.oup.com/femsre/article/23/1/13/575607)
6. [Structure and function of enzymes involved in the methanogenic pathway utilizing carbon dioxide and molecular hydrogen (ScienceDirect)](https://www.sciencedirect.com/science/article/abs/pii/S1389172302802328)
7. [CO2-Fixation Strategies in Energy Extremophiles: What Can We Learn From Acetogens? Frontiers in Microbiology (2020)](https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.00486/full)
8. [Evolving understanding of rumen methanogen ecophysiology (PMC, 2023)](https://pmc.ncbi.nlm.nih.gov/articles/PMC10658910/)
9. [Active site structures for formate dehydrogenases and formylmethanofuran dehydrogenases. Journal of Biological Chemistry](https://www.jbc.org/article/S0021925820339223/pdf)
10. [All-in-One CO2 Capture and Transformation: Lessons from Formylmethanofuran Dehydrogenases (PMC, 2024)](https://pmc.ncbi.nlm.nih.gov/articles/PMC11656701/)
11. [Comparative genomics reveals electron transfer and syntrophic mechanisms differentiating methanotrophic and methanogenic archaea. PLOS Biology (2021)](https://journals.plos.org/plosbiology/article?id=10.1371%2Fjournal.pbio.3001508)
12. [Trace Metal Requirements for Microbial Enzymes Involved in the Production and Consumption of Methane and Nitrous Oxide. Frontiers in Microbiology (2012)](https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2012.00061/full)
13. [Formylmethanofuran dehydrogenases from methanogenic Archaea: substrate specificity, EPR properties and reversible inactivation by cyanide (PubMed)](https://pubmed.ncbi.nlm.nih.gov/8125106/)
14. [Molybdenum- and tungsten-containing formate dehydrogenases and formylmethanofuran dehydrogenases: Structure, mechanism, and cofactor insertion (PMC, 2019)](https://pmc.ncbi.nlm.nih.gov/articles/PMC6295890/)
15. [Early bioenergetic evolution (PMC, 2013)](https://pmc.ncbi.nlm.nih.gov/articles/PMC3685469/)
16. [Bioelectrocatalytic CO2 Reduction by Mo-Dependent Formylmethanofuran Dehydrogenase. Angewandte Chemie International Edition (2023)](https://onlinelibrary.wiley.com/doi/full/10.1002/anie.202311981)
17. [Ethane-oxidising archaea couple CO2 generation to F420 reduction, Nature Communications](https://www.nature.com/articles/s41467-024-53338-7)
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*Topic: Encyclopedia › Life and health › Microorganisms and fungi › Archaea › Methanogens and methanogenesis › CO2-reduction (hydrogenotrophic) methanogenesis*
*Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 21, 2026 · Edited: Sep 30, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
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