Dissimilatory Nitrate Reductase from Bradyrhizobium sp. (Lupinus): Subcellular Location, Catalytic Properties, and Characterization of the Active Enzyme Forms

Subcellular location, chlorate specificity, and sensitivity to micromolar concentrations of azide suggest that most of the anaerobically induced nitrate reductase (NR) activity in Bradyrhizobium sp. (Lupinus) could be ascribed to the membrane type of bacterial dissimilatory NRs. Two active complexes of the enzyme, NR_I of 140 kDa and NR_II of 190 kDa, were detected in membranes of the nitrate-respiring USDA strain 3045. Both enzyme forms were purified to homogeneity. Obtained specific antibodies showed that these native species were immunologically closely related and composed of largely similar 126-kDa, 65-kDa, and 25-kDa subunits. The finding that NR_I and NR_II share common epitopes suggests that they may not be different species, but rather two forms of the same enzyme.