Coenzyme B is a coenzyme required for redox reactions in

methanogen Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They are prokaryotic and belong to the domain Archaea. All known methanogens are members of the archaeal phylum Euryarchaeota. Methanogens are com ...

s. The full chemical name of coenzyme B is 7-mercaptoheptanoylthreoninephosphate. The molecule contains a thiol, which is its principal site of reaction. Coenzyme B reacts with 2-methylthioethanesulfonate (methyl- Coenzyme M, abbreviated ), to release methane in

methanogenesis Methanogenesis or biomethanation is the formation of methane coupled to energy conservation by microbes known as methanogens. Organisms capable of producing methane for energy conservation have been identified only from the domain Archaea, a group ...

: : + HS–CoB → + CoB–S–S–CoM This conversion is catalyzed by the enzyme

methyl coenzyme M reductase In enzymology, coenzyme-B sulfoethylthiotransferase, also known as methyl-coenzyme M reductase (MCR) or most systematically as 2-(methylthio)ethanesulfonate:N-(7-thioheptanoyl)-3-O-phosphothreonine S-(2-sulfoethyl)thiotransferase is an enzyme that ...

, which contains cofactor F430 as the prosthetic group. A related conversion that utilizes both HS-CoB and HS-CoM is the reduction of

fumarate Fumaric acid is an organic compound with the formula HO2CCH=CHCO2H. A white solid, fumaric acid occurs widely in nature. It has a fruit-like taste and has been used as a food additive. Its E number is E297. The salts and esters are known as f ...

to succinate, catalyzed by fumarate reductase: :HS–CoM + HS–CoB + ⁻ → ⁻ + CoB–S–S–CoM

Importance of Coenzyme B in Methanogenesis

Coenzyme B is an important component in the terminal step of methane biogenesis. It acts as a two electron-donor to reduce coenzyme M (methyl-coenzyme) into two molecules a methane and a heterodisulfide. Two separate experiment that were performed, one with coenzyme B and other without coenzyme B, indicated that using coenzyme B before the formation of the methane molecule, results in a more efficient and consistent bond cleavage.

References

Coenzymes Thiols Carboxamides {{Enzyme-stub