Hydrogenases from Desulfovibrio are found to catalyze hydrogen uptake with low potential multiheme cytochromes, such as cytochrome c3, acting as acceptors. The production of Fe-only hydrogenase from Desulfovibrio vulgaris Hildenborough was improved with respect to the growth phase and media to determine the best large-scale bacteria growth conditions. The interaction and electron transfer from Fe-only hydrogenase to multiheme cytochrome has been studied in detail by both BLAcore and steady-state measurements. The electron transfer between [Fe] hydrogenase and cytochrome c3 appears to be a cooperative phenomenon (h = 1.37). This behavior could be related to the conductivity properties of multihemic cytochromes. An apparent dissociation constant was determined (2 x 10(-7) M). The importance of the cooperativity for contrasting models proposed to describe the functional role of the hydrogenase/cytochrome c3 complex is discussed. Presently, the only determined structure is from [NiFe] hydrogenase and there are no obvious similarities between [NiFe] and [Fe] hydrogenase. Furthermore, no crystallographic data are available concerning [Fe] hydrogenase. The first results on crystallization and X-ray crystallography are reported.