Fine structure of iron ion in deoxyhemoglobin and deoxymyoglobin

To study the mechanism of oxygen binding of hemoglobin and myoglobin the electronic state of the central Fe²⁺ion was determined by means of magnetic susceptibility measurements. The paramagnetic saturation under high magnetic field of a superconducting magnet and the torque of a single crystal of hemoglobin were also studied. It was found that the fine structure of the lowest ground-state energy level (⁵B2) of ferrous ion in hemoglobin and myoglobin could be well represented by the spin Hamiltonian . The value of determined from the susceptibility measurements and from the field dependence of magnetization was 5 cm^-1. From the torque measurements, the values of and were also estimated to be 5.3 and 0.9 cm^-1, respectively.