Spin States of Divalent Iron in Anhydrohemoglobin

Mössbauer spectra of anhydrohemoglobin establish the existence of two ferrous iron spin states in anhydrohemoglobin. Magnetic susceptibility measurements show that anhydrohemoglobin is paramagnetic and has an effective magnetic moment per iron atom of 3.5 ± 0.1 μ_B at low temperatures. In conjunction with the susceptibility results, the Mössbauer spectra indicate that the iron in anhydrohemoglobin is distributed between high and low spin states in roughly equal amounts.