Purification and characterization of a membrane-bound hydrogenase from Sporomusa sphaeroides involved in energy-transducing electron transport.

Abstract

Hydrogenase was solubilized from the cytoplasmic membrane fraction of betaine-grown Sporomusa sphaeroides, and the enzyme was purified under oxic conditions. The oxygen-sensitive enzyme was partially reactivated under reducing conditions, resulting in a maximal activity of 19.8 μmol H2 oxidized min-1 (mg protein)-1 with benzyl viologen as electron acceptor and an apparent Km value for H2 of 341 μM. The molecular mass of the native protein estimated by native PAGE and gel filtration was 122 and 130 kDa, respectively. SDS-PAGE revealed two polypeptides with molecular masses of 65 and 37 kDa, present in a 1:1 ratio. The native protein contained 15.6 +/- 1.7 mol Fe, 11.4 +/- 1.4 mol S2-, and 0.6 mol Ni per mol enzyme. The hydrogenase coupled with viologen dyes, but not with other various artificial electron carriers, FAD, FMN, or NAD(P)+. The amino acid sequence of the N-termini of the subunits showed a high degree of similarity to eubacterial membrane-bound uptake hydrogenases. Washed membranes catalyzed a H2-dependent cytochrome b reduction at a rate of 0.18 nmol min-1 (mg protein)-1.