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Wolfe cycle

The Wolfe Cycle is a methanogenic pathway used by archaea; the archaeon takes H2 and CO2 and cycles them through a various intermediates to create methane. The Wolfe Cycle is modified in different orders and classes of archaea as per the resource availability and requirements for each species, but it retains the same basic pathway. The pathway begins with the reducing carbon dioxide to formylmethanofuran. The last step uses heterodisulfide reductase (Hdr) to reduce heterodisulfide into Coenzyme B and Coenzyme M using Fe4S4 clusters. Evidence suggests this last step goes hand-in-hand with the first step, and feeds back into it, creating a cycle. At various points in the Wolfe Cycle, intermediates that are formed are taken out of the cycle to be used in other metabolic processes. Since intermediates are being taken out at various points in the cycle, there is also a replenishing (anaplerotic) reaction that feeds into the Wolfe cycle, this is to regenerate necessary intermediates for the cycle to continue. Overall, including the replenishing reaction, the Wolfe Cycle has a total of nine steps. While Obligate CO 2 {\displaystyle {\ce {CO2}}} reducing methanogens perform additional steps to reduce CO2 to CH 3 {\displaystyle {\ce {CH3}}} .

Discovery

In 1971, in a review published by Robert Stoner Wolfe, information regarding methanogenesis in M. bryantii was published. At the time, the only thing known about this process was that Coenzyme M was involved. In addition, methanogenesis was thought to follow a linear pathway. It was not until 1986 that the reduction of CO 2 {\displaystyle {\ce {CO2}}} to CH 4 {\displaystyle {\ce {CH4}}} was proposed to occur in a cycle when it was shown that Steps 8 and 1 are coupled.

Steps

The Wolfe Cycle follows multiple pathways, depending on the microbe. Below are generalized steps in the Wolfe Cycle.

steps reactants Enzymes Products used in cycle
1 CO 2 + MF + 2 H + {\displaystyle {\ce {CO2 + MF +2H+}}} Formyl-methanofuran dehydrogenase Formyl − MFR {\displaystyle {\ce {Formyl - MFR}}}
2 N − Formyl − MFR + H 4 MPT {\displaystyle {\ce {N-Formyl - MFR + H4MPT}}} Formyltransferase N − Formyl − H 4 MPT {\displaystyle {\ce {N-Formyl-H4MPT}}}
3 Formyl − H 4 MPT + H + {\displaystyle {\ce {Formyl - H4MPT + H+}}} methenyl-H4MPT cyclohydrolase methenyl − H 4 MPT {\displaystyle {\ce {methenyl-H4MPT}}}
4 Methenyl − H 4 MPT + F 420 H 2 {\displaystyle {\ce {Methenyl - H4MPT + F420H2}}} methylene-H4MPT dehydrogenase methylene − H 4 MPT {\displaystyle {\ce {methylene-H4MPT}}}
5 Methylene − H 4 MPT + F 420 H 2 {\displaystyle {\ce {Methylene - H4MPT + F420H2}}} methylene-H4MPT reductase methyl − H 4 MPT {\displaystyle {\ce {methyl-H4MPT}}}
6 methyl − H 4 MPT + HS − CoM {\displaystyle {\ce {methyl-H4MPT + HS-CoM}}} methyl-H4MPT/HSCoM methyl transferase CH 3 − S − CoM {\displaystyle {\ce {CH3-S-CoM}}}
7 CH 3 − S − CoM + HS − CoB {\displaystyle {\ce {CH3-S-CoM + HS-CoB}}} methyl-S-CoM reductase CoM − S − S − CoB {\displaystyle {\ce {CoM-S-S-CoB}}}
8 CoM − S − S − CoB + Fdx ( ferredoxin ) {\displaystyle {\ce {CoM-S-S-CoB + Fdx (ferredoxin)}}} electron bifurcating hydrogenase-heterodisulfide reductase complex Fdx 2 − + HS − CoB + HS − CoM {\displaystyle {\ce {Fdx^2- + HS-CoB + HS-CoM}}}
9 F 420 + H 2 + HCO 2 H {\displaystyle {\ce {F420 + H2 + HCO2H}}} F420-reducing hydrogenase CO 2 + F 420 H {\displaystyle {\ce {CO2 + F420H}}}

References

  1. ^ Thauer, Rudolf K. (2012-09-18). "The Wolfe cycle comes full circle". Proceedings of the National Academy of Sciences. 109 (38): 15084–15085. Bibcode:2012PNAS..10915084T. doi:10.1073/pnas.1213193109. ISSN 0027-8424. PMC 3458314. PMID 22955879.
  2. Wu, Jue; Chen, Shi-Lu (2022-02-18). "Key Piece in the Wolfe Cycle of Methanogenesis: The S–S Bond Dissociation Conducted by Noncubane [Fe 4 S 4 ] Cluster-Dependent Heterodisulfide Reductase". ACS Catalysis. 12 (4): 2606–2622. doi:10.1021/acscatal.1c06036. ISSN 2155-5435.
  3. Vo, Chi Hung; Goyal, Nishu; Karimi, Iftekhar A; Kraft, Markus (January 2020). "First Observation of an Acetate Switch in a Methanogenic Autotroph ( Methanococcus maripaludis S2)". Microbiology Insights. 13: 117863612094530. doi:10.1177/1178636120945300. ISSN 1178-6361. PMC 7416134. PMID 32843840.
  4. ^ Balch, William E.; Ferry, James G. (2021-01-01), Poole, Robert K.; Kelly, David J. (eds.), "Chapter One - The Wolfe cycle of carbon dioxide reduction to methane revisited and the Ralph Stoner Wolfe legacy at 100 years", Advances in Microbial Physiology, 79, Academic Press: 1–23, doi:10.1016/bs.ampbs.2021.07.003, PMID 34836609, S2CID 244550528, retrieved 2023-11-27
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