The magnetic susceptibility of native soybean lipoxygenase-1. Implications for the symmetry of the iron environmental and the possible coordination of dioxygen to Fe(II)

Abstract

(1) The magnetic susceptibility of native soybean lipoxygenase-1, a non-heme iron dioxygenase, has been measured over the temperature range 10–170 K. (2) With the ground-state multiplet of its high-spin Fe(II) described by means of a spin Hamiltonian, the temperature dependence of the susceptibility is found to be consistent with the zero-field splitting parameters, D and E, within the limits D = 8.5 cm −1, ∣ E D ∣ = 0.14 and D = 11.9 cm −1,∣ E D ∣ = 0 . The best agreement with the experimental data was obtained for D = 11.1 cm −1 and ∣ E D ∣ = 0.04 . Less satisfactory agreement could be obtained with negative D values in the range −6.9 to −5.5 cm −1 and ∣ E D ∣ < 0.01 . These values are compatible with an iron environment of largely axial symmetry, possibly with a small rhombic distortion. (3) No evidence could be found from the magnetic studied (in the temperature range 27–170K) that dioxygen should be coordinated to the iron of the native enzyme form.