Nitrogenase of Klebsiella pneumoniae: electron-paramagnetic-resonance studies on the catalytic mechanism

The enzyme nitrogenase has been purified in different laboratories from a number of sources and studied extensively (Burris, 1971; Hardy et al., 1971; Eady et al., 1972). It consists of two proteins, the smaller containing iron and labile sulphur and the larger molybdenum, iron and labile sulphur. Turn- over of the enzyme involves transfer of reducing equivalents from Na2S204 or other reducing sub- strates to the oxidizing substrate, which may be N2 or some other triple-bonded molecules, or H+ ions. The latter are always reduced to H2, although in the presence of other oxidizing substrates the rate of this reaction is inhibited to 20-25% of that in their absence. A bivalent cation, and ATP, which is hydrolysed to ADP, are always required.