Electron Paramagnetic Resonance (34 and 55 GHz) Studies of Hemoproteins

Abstract

Measurements of the 34 and 55 GHz electron paramagnetic resonance (E.P.R.) spectra of single type A crystals of metmyoglobin, metmyoglobin fluoride and methemoglobin and polycrystalline metmyoglobin and methemoglobin at 77 K are reported. The frequency dependence of the g-values of metmyoglobin, metmyoglobin fluoride, and methemoglobin is used to estimate the zero-field splitting (2D). It is found that (2D) [Formula: see text], (2D) (MbF) = (8.1 ± 1.0) cm−1, and 15 cm−1 <(2D) (HbH2O). The observed angular E.P.R. line width variation of these hemoproteins is compared with the variation predicted by a misorientation hypothesis. The frequency dependence of these line widths is also studied and shown to be consistent with a statistical variation in the zero-field splitting. The g-value and line width measurements are compared with those reported previously and the estimates of the zero-field splitting are compared with the values obtained using other measurement techniques.