Vanadium nitrogenase of Azotobacter chroococcum. MgATP-dependent electron transfer within the protein complex.
The kinetics of MgATP-induced electron transfer from the Fe protein (Ac2V) to the VFe protein (AclV) of the vanadium-containing nitrogenase from Azotobacter chroococcum were studied by stopped-flow spectrophotometry at 23 degrees C at pH 7.2. They are very similar to those of the molybdenum nitrogenase of Klebsiella pneumoniae [Thorneley (1975) Biochem. J. 145, 391-396]. Extrapolation of the dependence of kobs. on [MgATP] to infinite MgATP concentration gave k = 46 s-1 for the first-order electron-transfer reaction that occurs with the Ac2V MgATPAclV complex. MgATP binds with an apparent KD = 230 +/- 10 microM and MgADP acts as a competitive inhibitor with Ki = 30 +/- 5 microM. The Fe protein and VFe protein associate with k greater than or equal to 3 x 10(7) M-1.s-1. A comparison of the dependences of kobs. for electron transfer on protein concentrations for the vanadium nitrogenase from A. chroococcum with those for the molybdenum nitrogenase from K. pneumoniae [Lowe & Thorneley (1984) Biochem. J. 224, 895-901] indicates that the proteins of the vanadium nitrogenase system form a weaker electron-transfer complex.
Thorneley
R N
RN
A.F.R.C. Institute of Plant Science Research, University of Sussex, Brighton, U.K.
Bergström
N H
NH
Eady
R R
RR
Lowe
D J
DJ
D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D001395:Azotobacter / Q000201:enzymology*; D004583:Electrons; D007700:Kinetics; D046911:Macromolecular Substances; D009591:Nitrogenase / Q000378:metabolism*
D046911:Macromolecular Substances; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D009591:Nitrogenase