The Hydrogenase-Nitrogenase Relationship in Nitrogen-Fixing Organisms

Abstract

Historically, an enzyme catalyzing the reaction 2H⁺+2e^-→H² was first demonstrated by Stephenson and Stickland (1931) using extracts from Escherichia coli. A relationship between H²-metabolism and N²-fixation was recognized in the early 1940’s by P.W. Wilson and his coworkers (Phelps and Wilson, 1941; Wilson et al., 1942; Lee and Wilson, 1943; Green and Wilson, 1953; Hyndman et al., 1953). They detected a hydrogenase in Azotobacter and Rhizobium bacteroids which catalyzed the uptake of molecular hydrogen and which was particularly active under nitrogen-fixing conditions. In the past few years, the hydrogenase-nitrogenase relationship has been investigated with increasing efforts. Such renewed interest mainly comes from considerations to use H₂ -formation by photosynthetic organisms in projects of solar energy conversion. Consequently, since several agencies gave financial support to investigations in this field, the Output of publications has recently been increased explosively. It is not the scope of this communication to review the vast literature, particularly since articles on H₂ -metabolisms by different groups of microorganisms have recently become available. The reader is referred to the review articles by Schlegel and Schneider (1978) or Mortenson and Chen (1974) for fermentative bacteria, by Meyer et al. (1978) or Schlegel and Schneider (1978) for photosynthetic bacteria, by Dixon (1978), Albrecht et al. (1979) or Walker and Yates (1978) for Rhizobium and Azotobacter, by Hallenbeck and Benemann (1979) or Bothe et al. (1978) for blue–green algae and by Kessler (1974), Bishop et al. (1977) or Ben-Amotz (1979) for green algae. This communication will summarize aspects of the hydrogenase-nitrogenase relationship with special emphasis on blue-green algae which are in the centre of our own interest.