Isolation and Characterization of Flavoredoxin, a New Flavoprotein That Permits in Vitro Reconstitution of an Electron Transfer Chain from Molecular Hydrogen to Sulfite Reduction in the Bacterium Desulfovibrio gigas

A new FMN-containing fiavoprotein isolated from Desulfovibrio gigas provided maximum coupling efficiency for the reduction of bisulfite from molecular H2. This protein, which is distinct from flavodoxin and for which the name flavoredoxin is proposed, is required for reconstitution of an electron transfer chain between hydrogenase and bisulfite reductase. A Ca2+-binding protein functions as a modulator in the presence of Ca2+ in the process. The finding of a membrane-bound cytochrome c with a molecular weight of 104,000 Da that is also active in this electron transfer chain provides an explanation for the energetic linkage between periplasmic and cytoplasmic proteins in this sulfate-reducing bacterium.