Redox properties and electron paramagnetic resonance spectroscopy of the transition state complex of Azotobacter vinelandii nitrogenase.
Nitrogenase is a two-component metalloenzyme that catalyzes a MgATP hydrolysis driven reduction of substrates. Aluminum fluoride plus MgADP inhibits nitrogenase by stabilizing an intermediate of the on-enzyme MgATP hydrolysis reaction. We report here the redox properties and electron paramagnetic resonance (EPR) signals of the aluminum fluoride-MgADP stabilized nitrogenase complex of Azotobacter vinelandii. Complex formation lowers the midpoint potential of the [4Fe-4S] cluster in the Fe protein. Also, the two-electron reaction of the unique [8Fe-7S] cluster in the MoFe protein is split in two one-electron reactions both with lower midpoint potentials. Furthermore, a change in spin-state of the two-electron oxidized [8Fe-7S] cluster is observed. The implications of these findings for the mechanism of MgATP hydrolysis driven electron transport within the nitrogenase protein complex are discussed.
Department of Biomolecular Sciences, Agricultural University, Wageningen, The Netherlands.
J H
JH
Spee
A F
AF
Arendsen
H
H
Wassink
S J
SJ
Marritt
W R
WR
Hagen
H
H
Haaker
D000244:Adenosine Diphosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000737:chemistry*; D017607:Aluminum Compounds / Q000494:pharmacology; D016948:Azotobacter vinelandii / Q000201:enzymology*; D004578:Electron Spin Resonance Spectroscopy; D005459:Fluorides / Q000494:pharmacology; D006868:Hydrolysis; D007506:Iron-Sulfur Proteins / Q000737:chemistry; D008667:Metalloproteins / Q000737:chemistry*; D008982:Molybdenum / Q000737:chemistry; D009591:Nitrogenase / Q000737:chemistry*; D010084:Oxidation-Reduction; D011199:Potentiometry; D011487:Protein Conformation
D017607:Aluminum Compounds; D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D000244:Adenosine Diphosphate; D008982:Molybdenum; D009591:Nitrogenase; D000251:Adenosine Triphosphatases; D005459:Fluorides; C032311:aluminum fluoride