Nickel Tetrapyrroles in Methanogenic Bacteria: Structure, Function and Biosynthesis

Abstract

Most methanogenic bacteria can grow on H₂ plus CO₂ as sole energy source; CO₂ is reduced to methane: 4 H₂ + CO₂ → CH₄ + 4 H₂O. The exergonic step in this process is probably the reduction of methyl CoM to methane. This reaction is catalyzed by the methyl CoM reductase, the prosthetic group of which is factor F₄₃₀. This factor contains nickel and has been shown to have a nickel tetrapyrrole structure. The involvement of a nickel tetrapyrrole in methane formation explains why growth of all methanogens is dependent on nickel.