title: Exchange integral for a variety of tetranuclear ferredoxins.
abstract: The temperature dependence of EPR spectra of oxidized [4Fe-4S](-1,-2) ferredoxins (previously designated HiPIP) and a reduced [4Fe-4S](-2,-3) ferredoxin have been analyzed so as to determine the energy of a low-lying excited electronic state. The values obtained were: Center S-3 from beef heart, 44 cm-1; Center S-3 from mung bean, 53 cm-1; the [4Fe-4S](-1,-2) ferredoxin from Thermus thermophilus, 78 cm-1; Center N-2 of NADH ubiquinone reductase, 83 cm-1. Increasing axial distortion in the EPR spectra of the [4Fe-4S](-1,-2), ferrodoxins was associated with higher energy differences. Center N-2, a [Fe-4S](-2,-3) iron-sulfur cluster does not fit this relationship.
mesh_terms: D000818:Animals; D002417:Cattle; D004578:Electron Spin Resonance Spectroscopy; D005288:Ferredoxins; D007506:Iron-Sulfur Proteins; D009206:Myocardium / Q000032:analysis; D010084:Oxidation-Reduction; D011487:Protein Conformation; D013696:Temperature; D013824:Thermus / Q000032:analysis
chemical_list: D005288:Ferredoxins; D007506:Iron-Sulfur Proteins