An analysis of the g values in semi-met forms of hemerythrin and in related proteins

The two semi-met (FeIII, FeII) forms of hemerythrin prepared by either oxidation of the deoxy form or reduction of the met form, exhibit rather different EPR spectra. It is shown that a very weak difference in the rhombic distortion of the ferrous site is sufficient to account for this large shift of the g values. It is proposed that the important departure from g = 2.00 and the large anisotropy of the g tensor reflect directly the octahedral coordination of the ferrous ion. Such a coordination could then be present in other proteins which contain binuclear clusters characterized by similar EPR spectra.