Nitrogenases of Klebsiella pneumoniae and Azotobacter chroococum. Complex formation between the component proteins.

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.