2Fe2S centers

2Fe.2S iron sulfur center from Rieske protein of the bc₁-complex

Note the 2 histidine and 2 cysteine ligands

Half-cell reaction:
2Fe2S ==> 2Fe2S⁺ + e^-

Midpoint redox potential: E_{m, pH 7} = 290 mV (~100 mV in dioxygenases)
No. of electrons: z=1
No. of protons: n=0 or 1, depending on protein, pH, pK

2Fe.2S iron sulfur center from ferredoxin

Note the 4 cysteine ligands

Half-cell reaction:
2Fe2S ==> 2Fe2S⁺ + e^-

Midpoint redox potential: E_{m, pH 7} = -290 - -400 mV
No. of electrons: z=1
No. of protons: n=0 or 1, depending on protein, pH, pK

©Copyright 1996, Antony Crofts, University of Illinois at Urbana-Champaign, a-crofts@uiuc.edu