Wood–Ljungdahl pathway

The Wood–Ljungdahl pathway is a set of biochemical reactions used by some bacteria. It is also known as the reductive acetyl-coenzyme A (Acetyl-CoA) pathway. This pathway enables these organisms to use hydrogen as an electron donor, and carbon dioxide as an electron acceptor and as a building block for biosynthesis.

In this pathway carbon dioxide is reduced to carbon monoxide and formic acid or directly into a formyl group, the formyl group is reduced to a methyl group and then combined with the carbon monoxide and Coenzyme A to produce acetyl-CoA. Two specific enzymes participate on the carbon monoxide side of the pathway: CO Dehydrogenase and acetyl-CoA synthase. The former catalyzes the reduction of the CO₂ and the latter combines the resulting CO with a methyl group to give acetyl-CoA.

Some anaerobic bacteria use the Wood–Ljungdahl pathway in reverse to break down acetate. For example, Sulfate reducing bacteria oxidize acetate completely to CO₂ and H₂ coupled with the reduction of sulfate to sulfide. When operating in the reverse direction, the acetyl-CoA synthase is sometimes called acetyl-CoA decarbonylase.

Not to be confused with the Wood-Ljungdahl pathway, an evolutionarily related but biochemically distinct pathway named the Wolfe Cycle occurs exclusively in some methanogenic archaea called methanogens. In these anaerobic archaea, the Wolfe Cycle functions as a methanogenesis pathway to reduce CO₂ into methane with electron donors such as hydrogen and formate.