title: Nitrogenases of Klebsiella pneumoniae and Azotobacter chroococum. Complex formation between the component proteins.
abstract: 1. Sedimentation velocity analyses of mixtures of highly purified component proteins of Azotobacter chroococcum are consistent with the formation of a tight 1 : 1 complex in the absence of Na2 S2 O4. 1 : 1 complex formation between complementary proteins from A. chroococcum and Klebsiella pneumoniae was also observed. The addition of 5 mM Na2 S2 O4 weakened the interaction between the A. chroococcum proteins and also the interaction between complementary proteins of A. chroococcum and K. pneumoniae. 2. Steady-state kinetic data for acetylene reduction at low protein concentrations have been used to calculate association constants at 30 degrees C for the 1 : 1 protein complexes of nitrogenase proteins from A. chroococcum, K. pneumoniae and mixtures of complementary proteins from both organisms. Values centered around 3 - 10(7) M-1 were obtained. 3. The temperature dependence of the association constant for the complex formed by the K. pneumoniae proteins exhibited a sharp break at 17 degrees C with deltaH = 0 and deltaH = 418 kJ - mol-1 above and below 17 degrees C, respectively. 4. The Arrhenius plot for acetylene reduction by the complex formed by the K. pneumoniae proteins was linear over the range 12-40 degrees C with deltaH = 80 kJ - mol-1.
mesh_terms: D001395:Azotobacter / Q000201:enzymology*; D001665:Binding Sites; D007700:Kinetics; D007711:Klebsiella pneumoniae / Q000201:enzymology*; D046911:Macromolecular Substances; D008433:Mathematics; D008970:Molecular Weight; D009591:Nitrogenase / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D013045:Species Specificity; D013696:Temperature; D013816:Thermodynamics
chemical_list: D046911:Macromolecular Substances; D009591:Nitrogenase