Active site of hemerythrin. Iron electronic states and the binding of oxygen

Hemerythrin, a molecular oxygen-binding nonheme protein, found in marine organisms, binds a single oxygen molecule per protein subunit containing two Fe atoms.The nature of the oxygen binding and the electronic state of Fe in oxy-, de.oxy-, and oxidized forms of the protein subunits has been investigated by Mossbauer spectroscopy, magnetic susceptibility measurements, and b chemical means.Oxidized (met) hemerythrin derivatives show a single high-spin Fe(III) (S = 5/2) site for the two Fe atoms; these sites are then spin-coupled to give molecular diamagnetism.In deoxyhexnerythrin the single environment is high-spin Fe(II) (S = 2) with no evidence of spin-coupling shown by susceptibility measurements.The oxy-form of the protein shows two Fe environments, a result in contrast to a symmetrical oxo-bridge or superoxide anion previously proposed.The relation of these physical studies to other studies and a discussion of oxygen-binding in hemerythrin is given.