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 hy drolysis driven reduction of substrates, Aluminum fluoride plus MgADP inhibits nitrogenase by stabilizing an intermediate of the on-enzyme M gATP hydrolysis reaction. We report here the redox properties and elec tron paramagnetic resonance (EPR) signals of the aluminum fluoride-MgA DP stabilized nitrogenase complex of Azotobacter vinelandii. Complex f ormation lowers the midpoint potential of the [4Fe-4S] cluster in the Fe protein. Also, the two-electron reaction of the unique [8Fe-7S] clu ster in the MoFe protein is split in two one-electron reactions both w ith loner midpoint potentials. Furthermore, a change in spin-state of the tno-electron oxidized [8Fe-7S] cluster is observed. The implicatio ns of these findings for the mechanism of MgATP hydrolysis driven elec tron transport within the nitrogenase protein complex are discussed. ( C) 1998 Federation of European Biochemical Societies.