1.17.98.4 CO2 + reduced benzyl viologen - Escherichia coli formate + benzyl viologen - r 443386 1.17.98.4 formate + acceptor - Escherichia coli CO2 + reduced acceptor - ? 402641 1.17.98.4 formate + acceptor formate dehydrogenase H (FDHH) catalyses the first step in the formate hydrogen lyase (FHL) system Escherichia coli CO2 + reduced acceptor - ? 402641 1.17.98.4 formate + acceptor the transfer of the formate proton, H+(formate), from formate to the active site base Y- is thermodynamically coupled to two-electron oxidation of the formate molecule, thereby facilitating formation of CO2. Under normal physiological conditions, when electron flow is not limited by the terminal acceptor of electrons, the energy released upon oxidation of Mo(IV) centers by the Fe4S4 is used for deprotonation of YH(formate) and transfer of H+(formate) against the thermodynamic potential. This mechanism of proton release from FDH(Se) may play a physiological role in delivery of the formate proton H+(formate) to hydrogenase 3, which is the natural terminal acceptor of electrons for FDH(Se) Escherichia coli CO2 + reduced acceptor - ? 402641 1.17.98.4 formate + acceptor the reinterpretation of the crystal structure suggests a new reaction mechanism: In step I, formate binds directly to Mo, displacing Se-Cys140. In step II, the alpha-proton from formate may be transferred to the nearby His141 that acts as general base. In this step the CO2 molecule can be released and two electrons transferred to Mo. Alternatively, step II may involve a selenium-carboxylated intermediate. In step III, electrons from Mo(IV) are transferred via the [4Fe-4S] center to an external electron acceptor and the catalytic cycle is completed Escherichia coli CO2 + reduced acceptor - ? 402641 1.17.98.4 formate + benzyl viologen - Escherichia coli CO2 + reduced benzyl viologen - ? 189133 1.17.98.4 formate + benzyl viologen - Archaeoglobus fulgidus CO2 + reduced benzyl viologen - ? 189133 1.17.98.4 formate + benzyl viologen - Escherichia coli CO2 + reduced benzyl viologen - r 189133 1.17.98.4 formate + benzyl viologen the transfer of the formate proton, H+(formate), from formate to the active site base Y- is thermodynamically coupled to two-electron oxidation of the formate molecule, thereby facilitating formation of CO2. Under normal physiological conditions, when electron flow is not limited by the terminal acceptor of electrons, the energy released upon oxidation of Mo(IV) centers by the Fe4S4 is used for deprotonation of YH(formate) and transfer of H+(formate) against the thermodynamic potential. This mechanism of proton release from FDH(Se) may play a physiological role in delivery of the formate proton H+(formate) to hydrogenase 3, which is the natural terminal acceptor of electrons for FDH(Se) Escherichia coli CO2 + reduced benzyl viologen - ? 189133 1.17.98.4 formate + benzyl viologen FDH-H remains essentially unchanged when deuteroformate is used as a substrate Escherichia coli CO2 + reduced benzyl viologen - ? 189133 1.17.98.4 formate + benzyl viologen formate oxidation is not rate-limiting in the overall coupled reaction of formate oxidation and benzyl viologen reduction Escherichia coli CO2 + reduced benzyl viologen - ? 189133 1.17.98.4 formate + benzyl viologen ping-pong bi-bi kinetic mechanism Escherichia coli CO2 + reduced benzyl viologen - ? 189133 1.17.98.4 formate + benzyl viologen the enzyme may have a role in formate reuptake Archaeoglobus fulgidus CO2 + reduced benzyl viologen - ? 189133 1.17.98.4 formate + FAD - Methanococcus vannielii CO2 + FADH2 - ? 189144 1.17.98.4 formate + FAD - Methanococcus vannielii DSM 1224 CO2 + FADH2 - ? 189144 1.17.98.4 formate + FMN - Methanococcus vannielii CO2 + FMNH2 - ? 189143 1.17.98.4 formate + FMN - Methanococcus vannielii DSM 1224 CO2 + FMNH2 - ? 189143 1.17.98.4 formate + HycB the hydrogenase 3 Fe-S subunit HycB may represent the electron transfer partner of FDH-H Escherichia coli CO2 + reduced HycB - ? 402643 1.17.98.4 formate + methyl viologen - Escherichia coli CO2 + reduced methyl viologen - ? 189138 1.17.98.4 formate + oxidized coenzyme F420 - Methanococcus vannielii CO2 + reduced coenzyme F420 - ? 427444 1.17.98.4 formate + oxidized coenzyme F420 - Methanococcus vannielii DSM 1224 CO2 + reduced coenzyme F420 - ? 427444 1.17.98.4 formate + [NiFe]-hydrogenase 3 - Escherichia coli CO2 + a [reduced hydrogenase] - ? 457160 1.17.98.4 formate + [NiFe]-hydrogenase 3 - Escherichia coli CO2 + reduced [NiFe]-hydrogenase 3 - ? 457978 1.17.98.4 additional information Escherichia coli possesses two hydrogenases, Hyd-3 and Hyd-4. These, in conjunction with formate dehydrogenase H (Fdh-H), constitute distinct membrane-associated formate hydrogenlyases, FHL-1 and FHL-2, both catalyzing the decomposition of formate to H2 and CO2 during fermentative growth. FHL-1 is the major pathway at acidic pH. At alkaline pH formate increases an activity of Fdh-H and of Hyd-3 both but not of Hyd-4 Escherichia coli ? - ? 89 1.17.98.4 additional information hydrogenase 3 but not hydrogenase 4 is the major enzyme in hydrogen gas production by Escherichia coli formate hydrogenlyase at acidic pH and in the presence of external formate Escherichia coli ? - ? 89 1.17.98.4 additional information physiological role of FSH-O is to ensure rapid adaptation during a shift from aerobiosis to anaerobiosis Escherichia coli ? - ? 89 1.17.98.4 additional information the enzyme catalyzes carbon exchange between carbon dioxide and formate in the absence of other electron acceptors, confirming the ping-pong reaction mechanism Escherichia coli ? - ? 89 1.17.98.4 additional information no activity with NADP+ or NAD+ Methanococcus vannielii ? - ? 89 1.17.98.4 additional information no activity with NADP+ or NAD+ Methanococcus vannielii DSM 1224 ? - ? 89