title: Low-potential cytochrome b as an essential electron-transport component of menaquinone reduction by formate in Vibrio succinogenes.
abstract: Incorporation of the electron-transport enzymes of Vibrio succinogenes into liposomes was used to investigate the question of whether, in this organism, a cytochrome b is involved in electron transport from formate to fumarate on the formate side of menaquinone. (1) Formate dehydrogenase lacking cytochrome b was prepared by splitting the cytochrome from the formate dehydrogenase complex. The enzyme consisted of two different subunits (Mr 110 000 and 20 000), catalyzed the reduction of 2,3-dimethyl-1,4-naphthoquinone by formate, and could be incorporated into liposomes. (2) The modified enzyme did not restore electron transport from formate to fumarate when incorporated into liposomes together with vitamin K-1 (instead of menaquinone) and fumarate reductase complex. In contrast, restoration was observed in liposomes that contained formate dehydrogenase with cytochrome b (Em = -224 mV), in addition to the subunits mentioned above (formate dehydrogenase complex). (3) In the liposomes containing formate dehydrogenase complex and fumarate reductase complex, the response of the cytochrome b of the formate dehydrogenase complex was consistent with its interaction on the formate side of menaquinone in a linear sequence of the components. The low-potential cytochrome b associated with fumarate reductase complex was not reducible by formate under any condition. It is concluded that the low-potential cytochrome b of the formate dehydrogenase complex is an essential component in the electron transport from formate to menaquinone. The low-potential cytochrome b of the fumarate reductase complex could not replace the former cytochrome in restoring electron-transport activity.
mesh_terms: D003573:Cytochrome b Group / Q000378:metabolism*; D004579:Electron Transport; D005560:Formate Dehydrogenases / Q000378:metabolism; D005561:Formates / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism; D008970:Molecular Weight; D009097:Multienzyme Complexes / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors; D014733:Vibrio / Q000201:enzymology*; D014812:Vitamin K / Q000378:metabolism*
chemical_list: D003573:Cytochrome b Group; D005561:Formates; D008081:Liposomes; D009097:Multienzyme Complexes; C030544:formic acid; D014812:Vitamin K; D010088:Oxidoreductases; D005560:Formate Dehydrogenases; D044925:Oxidoreductases Acting on CH-CH Group Donors; C020155:fumarate reductase (NADH)