H-1-NMR STUDIES OF THE OXIDIZED AND PARTIALLY REDUCED 2(4FE-4S) FERREDOXIN FROM CLOSTRIDIUM-PASTEURIANUM

1H NMR spectra of the oxidized ferredoxin from Clostridium pasteurianum, which contains two weakly paramagnetic Fe4S42− clusters, have been recorded and 1H nuclear Overhauser effects have been used to determine proton pairs of β-CH2 of the cluster-coordinated cysteines. The shift dependence on the dihedral angles between the Fe-S-C and S-C-H planes has been discussed. The size of the hyperfine shifts and their temperature dependence can be reproduced with a model in which some of the antiferromagnetic coupling constants between Fe(III) and Fe(II) ions are smaller than the other antiferromagnetic coupling constants. 1H saturation transfer experiments on the partially reduced protein provides an estimate of the lower limit of the intermolecular electron transfer between the fully oxidized, intermediate, and fully reduced species. © 1990, American Chemical Society. All rights reserved.