Structure of the Molybdoferredoxin Complex from Clostridium pasteurianum and Isolation of Its Subunits

Abstract

Highly purified molybdoferredoxin, with a specific activity of 2.6 μmoles of acetylene reduced per min per mg of protein, was obtained from Clostridium pasteurianum . The protein at concentrations above 5 mg/ml exists in solution as a tetrameric complex with two subunits each of about 60,000 and 50,000 daltons. Two atoms of molybdenum are present per protein molecule of 220,000 daltons. The S 0 20, w was found to be 10.5. The tetramer dissociates into a dimer as demonstrated by a decreasing sedimentation coefficient with decreasing protein concentration. At low p H and ionic strength, further dissociation into the monomers is achieved. A method for the isolation of the protein subunits is described.