The Fe-Only Nitrogenase from Rhodobacter Capsulatus: 1. Catalytic and EPR-Spectroscopic Properties of the FeFe Protein

Abstract

A very rapid and effective procedure for the separation and purification of the component proteins (Fe protein, FeFe protein) of the iron-only nitrogenase (Fe nitrogenase) from a Rhodobacter capsulatus mutant strain (ΔnifHDK, ΔmodABCD; provided by Prof. Dr. W. Klipp, Universität Bochum) has recently been developed (Schneider et al., 1994; Schneider et al., 1997). Based on this procedure, at Fe protein: FeFe protein molar ratios of approximately 40:1, the following, remarkably high specific activities were achieved: 260 (C₂H₄ from C₂H₂), 350 (NH₃ formation) and 2400 (H₂ evolution) nmol product formed per min/mg of protein. The most striking catalytic characteristic of the Fe nitrogenase is its extraordinary high H₂-evolving activity, in vivo (Krahn et al., 1996) as well as in vitro (Schneider et al., 1997). In the presence of competing substrates (N₂, C₂H₂), the H₂ production is only weakly “inhibited”, resulting in reaction rates which are even severalfold higher than the rates obtained with the conventional Mo nitrogenase under analogous conditions.