A novel S = 3/2 EPR signal associated with native Fe‐proteins of nitrogenase

Abstract

In addition to their g = 1.94 EPR signal, nitrogenase Fe-proteins from Azotobacter vinelandii, Azotobacter chroococcum and Klebsiella pneumoniae exhibit a weak EPR signal with g N 5. Temperature dependence of the signal was consistent with an S= 312 system with negative zero-field splitting, D =-5 f 0.7 cm-l. The m, = f 312 ground state doublet gives rise to a transition with fl= 5.90 and the transition within the excited m,= + l/2 doublet has a split g,"=4.8, 3.4. Quantitation gave 0.6 to 0.8 spin.mol-' which summed with -the spin intensity of the S= l/2 g= 1.94 line to roughly 1 spin/mol. MgATP and MgADP decreased the intensity of the S= 312 signal with no concomitant changes in intensity of the S= l/2 signal.

Formation and characterization of a transition state complex of Azotobacter vinelandii nitrogenase

“…A1F4) complex, 2 mM sodium dithionite and 500 mM NaC1 in 50 mM TES/NaOH, pH 7.4. The EPR conditions for the measurements of the FeMoco S = 3/2 signal and the signals of oxidized P-clusters were described by Pierik et al [16] and the EPR conditions for the measurements of the Av2 S = 1/2 and S = 3/2 signals were described by Hagen et al [17].…”

A Bridging [4Fe-4S] Cluster and Nucleotide Binding Are Essential for Function of the Cfd1-Nbp35 Complex as a Scaffold in Iron-Sulfur Protein Maturation

“…A probable explanation could be that the [4Fe-4S] 1ϩ clusters are present as a physical mixture of S ϭ 1/2 and high spin states. Such physical spin mixtures are well characterized for the nitrogenase iron protein and activators of 2-hydroxyacyl-CoA dehydratases, which contain bridging [4Fe-4S] clusters (38,39). At the 50 M concentrations of Cfd1, Nbp35, or complex used previously (27), high spin states were not detected due to the low intensity and the broad nature of the EPR signals associated with such states (see Ref.…”

“…For the nitrogenase iron protein, another P-loop ATPase (38,40), the addition of nucleotides changes the rhombicity and spin state of its bound [4Fe-4S] 1ϩ clusters. Therefore, EPR spectra of the Cfd1-Nbp35 complex were recorded in the presence of Mg 2ϩ /ATP or Mg 2ϩ /GTP.…”

Multi‐frequency EPR and high‐resolution Mössbauer spectroscopy of a putative [6Fe‐6S] prismane‐cluster‐containing protein from Desulfovibrio vulgaris (Hildenborough)

“…Therefore, the transition intensities containing I + and I -have a factor (1 + cosz 0)/2 while the intensities containing I, have a factor sin' 8. The integration over the angle, 0, is performed explicitly by incrementing cos 0 as described in [39]. An example of the output of this program for increasing values of the applied magnetic field is shown in Fig.…”