Briefly Describe the Reductive Acetyl-CoA Pathway

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The Answer is The reductive acetyl-CoA pathway seems to be the most ancient CO₂ fixation and biomass assimilation; for example, in methanogens, up to 5% of the CO₂ they absorb is used in biosynthesis. It consists in the formation of an acetyl group using two CO₂ molecules converging from two different pathways. Formate is produced by reduction of CO₂ and transfer to tetrahydrofolate (THF), thus forming a C1 unit. The C1 unit is reduced to a methyl group, -CH₃. In methanogens, methane is formed from this C1 unit for energy gain. The methyl group can be fixed into biomass after being transferred to a tetrapyrrole (called TB and related to vitamin B₁₂). The second CO₂ molecule becomes

\mathrm{CO}_{3}^{-}

via carbon dioxide dehydrogenase

\mathrm{CO}_{3}^{-}

. is condensed with coenzyme A and the methyl group carried by TB to form acetyl-CoA.

Briefly Describe the Reductive Acetyl-CoA Pathway

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