The reduction of the unique co-factor F420 is necessary for methanogenesis because it serves as an electron carrier in the energy metabolism of methanogens. F420 is a flavin derivative that is structurally related to FAD and FMN, but it has a longer isoalloxazine ring and contains a 7,8-dimethyl-8-ribityllumazine (DMRL) moiety instead of an adenine or isoalloxazine. F420 can undergo a one-electron reduction to form F420H2, which has a lower reduction potential than NAD(P)H and can serve as an electron donor for a number of enzymes involved in methanogenesis.
Methanogens are strict anaerobes that use carbon dioxide and/or other substrates such as acetate, methanol, or methylamines as electron acceptors in the process of methane formation. F420H2 is a key electron donor for two of the enzymes involved in this process, namely methyl-coenzyme M reductase (MCR) and heterodisulfide reductase (Hdr). MCR catalyzes the final step in the pathway for methane formation from methyl-coenzyme M (CH3-S-CoM) and coenzyme B (CoB-SH), while Hdr is involved in the reduction of the heterodisulfide CoB-S-S-CoM and the generation of reducing equivalents for ATP synthesis. The reduction of F420H2 by hydrogenases and formate dehydrogenases also provides electrons for the reduction of carbon dioxide to methane.
In summary, the reduction of F420 is necessary for methanogenesis because it serves as a key electron carrier in the energy metabolism of methanogens and plays a crucial role in the conversion of carbon dioxide and/or other substrates to methane.