title: Quarter field resonance and integer-spin/half-spin interaction in the EPR of Thermus thermophilus ferredoxin. Possible new fingerprints for three iron clusters.
abstract: We describe two new characteristics of the EPR of the seven-iron containing ferredoxin from Thermus thermophilus. First, the reduced state of the 3Fe center, which has traditionally been considered to be EPR-silent, has been found to exhibit a delta m = 4 transition, which is unique for Fe-S centers. This signal is similar to that of high-spin Fe2+-EDTA and supports the suggestion that the ground electronic state of the 3Fe cluster is S = 2. Second, we have recorded the EPR spectrum of the fully reduced protein at 9 and 15 GHz and found that changes occur in the signal which are consistent with a weak electronic spin-spin interaction between the [4Fe-4S]+ (S = 1/2) and the reduced 3Fe center. A theoretical explanation is given for the observation of interaction signals with constant effective g values.
authors.forename: W R
authors.initials: WR
authors.lastname: Hagen
authors.forename: W R
authors.initials: WR
authors.lastname: Dunham
authors.forename: M K
authors.initials: MK
authors.lastname: Johnson
authors.forename: J A
authors.initials: JA
authors.lastname: Fee
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D005288:Ferredoxins; D007501:Iron; D008433:Mathematics; D013824:Thermus
chemical_list: D005288:Ferredoxins; D007501:Iron