Mouml;ssbauer spectroscopic studies of ferric myoglobin single crystals in a small applied magnetic field

摘要

Mouml;ssbauer experiments on single crystals of some ferric myoglobin (Mb) compounds which include high spin compounds (S=5/2), metMb and MbF, and a low spin compound (S=1/2), MbN3, have been done in the presence of a small external magnetic field perpendicular to the ggr; rays at liquid He temperature. The Mouml;ssbauer spectra of these compounds were analysed by a spin Hamiltonian formalism. For metMb and MbF, saturation fields of 480plusmn;5 and 510plusmn;5 kOe and quadrupole interactionseOVzz/2 of 1.10plusmn;0.05 and 0.70plusmn;0.05 mm secminus;1were obtained, respectively. The value of a hyperfine coupling constantAzwas determined from spectra obtained with the applied field nearly along theaaxis. The difference betweenAzandAperp;was less than 5percnt; and 4percnt; for metMb and MbF, respectively. For MbN3the following Mouml;ssbauer parameters were obtained: an asymmetry parameter eegr;=0.4plusmn;0.1, the quadrupole interactioneQVzz/2 =minus;2.10plusmn;0.05 mm secminus;1and an isomer shift=0.30plusmn;0.05 mm secminus;1. The axis of the largest component of an electric field gradient is rather close to the heme plane and deviates by 32deg; from one of four Fendash;N directions. Taking the results of EPR into account, it was found that the environment around the heme iron is lower than orthorhombic symmetry, being almost monoclinic symmetry.