title: Purification and characterization of the inactive MoFe protein (NifB-Kp1) of the nitrogenase from nifB mutants of Klebsiella pneumoniae.
abstract: The inactive MoFe protein of nitrogenase, NifB-Kp1, from two distinct nifB mutants of Klebsiella pneumoniae, Kp5058 (a nifB point mutant) and UNF1718 (a nifB, nifJ double mutant) has been purified and characterized. NifB-Kp1 can be activated by reaction with the iron-molybdenum cofactor, FeMoco, extracted from active MoFe protein. NifB-Kp1 purified from either source had similar properties and was contaminated with an approximately equimolar amount of protein of mol.wt. 21 000. Like active wild-type Kp1, it was an alpha 2 beta 2 tetramer, but it was far less stable than Kp1, deteriorating rapidly at temperatures above 8 degrees C or on mild oxidation. NifB-Kp1 preparations contained 0.4-0.9 Mo and 9.0 +/- 0.9 Fe atoms . mol-1 and, when activated by FeMoco, had a specific activity of approx. 500 units . mg-1. The Mo in our preparations was not associated with the e.p.r. signal normally observed from FeMoco. All preparations exhibited a weak gav. = 1.95 e.p.r. signal which was probably not associated with activatable protein.
mesh_terms: D003429:Cross Reactions; D004578:Electron Spin Resonance Spectroscopy; D004591:Electrophoresis, Polyacrylamide Gel; D005288:Ferredoxins / Q000302:isolation & purification*; D005779:Immunodiffusion; D007711:Klebsiella pneumoniae / Q000201:enzymology* / Q000235:genetics; D008970:Molecular Weight; D008983:Molybdoferredoxin / Q000276:immunology / Q000302:isolation & purification*; D009154:Mutation; D009591:Nitrogenase / Q000032:analysis*; D013053:Spectrophotometry
chemical_list: D005288:Ferredoxins; D008983:Molybdoferredoxin; D009591:Nitrogenase