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 reducing methanogens perform additional steps to reduce CO2 to .
Discovery
In 1971, in a review published by Robert Stoner Wolfe, information regarding methanogenesis in M. bryantii was published. The only thing known about this process, at the time, was that Coenzyme M was involved at some point of the pathway.[4] It was though that this was done through a linear cycle. It was not until 1986 that the reduction of to was proposed as a cycle when it was shown that the Steps 8 and 1 were coupled together.[4]
Steps
The Wolfe Cycle can be run in multiple ways depending on what microbe is using it, multiple pathways are available for different things to be produced. These are a generalized cycle of 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 |
