No abstract

Molybdoferredoxin from Clostridium pasteurianum W5 was fractionated into MoFd with two atoms of molybdenum per 220,000 daltons and a specific activity of 2.6 nmoles C2H2 reduced/min/mg protein and into a catalytically inactive species with an identical protein moiety but an incomplete active centre. Native MoFd is a tetramer composed of two 50,000 and two 60,000 dalton subunits. At low protein concentrations the tetramer is in equilibrium with a dimer. Under low ionic strength and at low pH further dissociation into monomers occurs. MoFd and azoferredoxin have distinct electron paramagnetic resonance spectra.The EPR spectrum of AzoFd and that of the combination of the two nitrogenase components undergoes characteristic changes upon addition of MgATP2-.(0.2 to 0.5 M NaCl in 0.05 Tris, pH 7.5, and 1 mM Na2S204; total volume 600 ml).