Coenzyme B (CoB)

Coenzyme B is a coenzyme required for redox reactions in methanogens. 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 CH₃-S-CoM), to release methane in methanogenesis: CH₃-S-CoM + HS-CoB → CH₄ + CoB-S-S-CoM

This conversion is catalyzed by the enzyme methyl coenzyme M reductase, which contains cofactor F430 as the prosthetic group. A related conversion that utilizes both HS-CoB and HS-CoM is the reduction of fumarate to succinate, catalyzed by fumarate reductase:

CH₃-S-CoM + HS-CoB ^-O₂CCH=CHCO₂^- → ^-O₂CCH₂-CH₂CO₂^- + CoB-S-S-CoM