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 $C O_{2}$ reducing methanogens perform additional steps to reduce CO₂ to $C H_{3}$ .

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 $C O_{2}$ to $C H_{4}$ 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	$C O_{2} + M F + 2 H^{+}$	Formyl-methanofuran dehydrogenase	$F o r m y l - M F R$
2	$N - F o r m y l - M F R + H_{4} M P T$	Formyltransferase	$N - F o r m y l - H_{4} M P T$
3	$F o r m y l - H_{4} M P T + H^{+}$	methenyl-H₄MPT cyclohydrolase	$m e t h e n y l - H_{4} M P T$
4	$M e t h e n y l - H_{4} M P T + F_{420} H_{2}$	methylene-H₄MPT dehydrogenase	$m e t h y l e n e - H_{4} M P T$
5	$M e t h y l e n e - H_{4} M P T + F_{420} H_{2}$	methylene-H₄MPT reductase	$m e t h y l - H_{4} M P T$
6	$m e t h y l - H_{4} M P T + H S - C o M$	methyl-H₄MPT/HSCoM methyl transferase	$C H_{3} - S - C o M$
7	$C H_{3} - S - C o M + H S - C o B$	methyl-S-CoM reductase	$C o M - S - S - C o B$
8	$C o M - S - S - C o B + F d x (f e r r e d o x i n)$	electron bifurcating hydrogenase-heterodisulfide reductase complex	$F d x^{2 -} + H S - C o B + H S - C o M$
9	$F_{420} + H_{2} + H C O_{2} H$	F₄₂₀-reducing hydrogenase	$C O_{2} + F_{420} H$

References

↑ ^1.0 ^1.1 ^1.2 ^1.3 ^1.4 ^1.5 ^1.6 ^1.7 Template:Cite journal
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↑ ^4.0 ^4.1 ^4.2 Template:Citation

[:1-1] 1.0 ^1.1 ^1.2 ^1.3 ^1.4 ^1.5 ^1.6 ^1.7 Template:Cite journal

[:0-2] Template:Cite journal

[3] Template:Cite journal

[:2-4] 4.0 ^4.1 ^4.2 Template:Citation

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Wolfe cycle

Discovery

Steps

References

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