Wolfe cycle

Methanogenic pathway
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.[1] 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.[1] The pathway begins with the reducing carbon dioxide to formylmethanofuran.[1] The last step uses heterodisulfide reductase (Hdr) to reduce heterodisulfide into Coenzyme B and Coenzyme M using Fe4S4 clusters.[1][2] Evidence suggests this last step goes hand-in-hand with the first step, and feeds back into it, creating a cycle.[1] At various points in the Wolfe Cycle, intermediates that are formed are taken out of the cycle to be used in other metabolic processes.[1][3] 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.[1] Overall, including the replenishing reaction, the Wolfe Cycle has a total of nine steps.[1] 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.[4] 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.[4]

Steps

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

steps reactants Enzymes[4] 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. ^ a b c d e f g h 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. ^ a b c 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