Electron paramagnetic resonance of single crystal oxycobaltmyoglobin and deoxycobaltmyoglobin

Single crystals of oxycobaltmyoglobin and deoxycobaltmyoglobin have been prepared and found to be isomorphous. The paramagnetic resonance spectra of deoxycobaltmyoglobin yield g(xx) = 2.33(0), g(yy) = 2.32(3), g(zz) = 2.02(8) with the z-axis parallel to the "heme" normal. The A(Co) and g tensors share the same principal axes with|A(Co) parallel| = 79 G and|A(Co)[unk]| = 6 G. A value of A(N) = 17.5 G was also obtained for the epsilon-N atom of the F8 histidine. There are two paramagnetic species in oxycobaltmyoglobin having apparently identical g-tensors (gxixi = 2.08(3), getaeta = 2.00(6), and gzetazeta = 1.98(9)) but different A(Co)-tensors. Furthermore, g values A(Co) do not share the same principal axes. The A(Co)-values for one of the species are (A(xx) = 16.7 G, A(yy) = 5.95 G, A(zz) = 9.3 G), they are all 40% larger for the other species. The two species are oriented 90 degrees to each other in the crystal. The results from electron paramagnetic resonance studies are consistent with a pi-bounded structure for (Co)MbO(2).