High frequency EPR predictions for the non-heme iron protein lipoxygenase

Soybean lipoxygenase-1 high frequency (greater than or equal to 70 GHz) EPR spectra at low magnetic field strengths (<2 Tesla) are predicted to have interdoublet transitions. Analysis of these transitions, if they are observed, will accurately measure all the zero field splitting (ZFS) terms for the second order spin Hamiltonian. The combination of interdoublet transitions with Kramers doubler transitions can be used as a sensitive, direct, measurement of D. The non-heme iron protein, lipoxygenase, in its activated S = 5/2 Fe+3 state, exhibits distributions in E/D. The effect of distributions in ZFS parameters on Kramers doublet transitions and interdoublet transitions are very different. These differences can be used to separate the components of the distribution in E/D: distributions in E and D. A first estimate of the separated distributions can be obtained from the relative amplitudes of the lowest Kramers doublet to the interdoublet transitions.