H2-uptake activity of the MoFe protein component of Azotobacter vinelandii nitrogenase

The MoFe protein from Azotobacter vinelandii catalyzes the reduction of methylene blue and other oxidants by H2 under anaerobic conditions. H2 uptake followed manometrically or by 3H2 transfer from the gas to aqueous phase occurs concomitantly with methylene blue disappearance monitored optically or coulometrically. The stoichiometry was found to be 1:1 methylene blue/H2. MoFe protein oxidized by transfer of approximately 4 e- seems to be the redox state of the protein most active in the catalytic step, although both the S2O4(2-)-reduced and 6-e- oxidized state have been shown to react, but at a much lower rate. The presence of H2 in the atmosphere above the MoFe protein offers increased protection against O2 inactivation.