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Methanogenic pathway From Wikipedia, the free encyclopedia
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 reducing methanogens perform additional steps to reduce CO2 to .
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 to was proposed to occur in a cycle when it was shown that Steps 8 and 1 are coupled.[4]
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 | Formyl-methanofuran dehydrogenase | ||
2 | Formyltransferase | ||
3 | methenyl-H4MPT cyclohydrolase | ||
4 | methylene-H4MPT dehydrogenase | ||
5 | methylene-H4MPT reductase | ||
6 | methyl-H4MPT/HSCoM methyl transferase | ||
7 | methyl-S-CoM reductase | ||
8 | electron bifurcating hydrogenase-heterodisulfide reductase complex | ||
9 | F420-reducing hydrogenase |
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