An electron resonance study of myoglobin single crystals

Abstract

The g-value end line width variations of the electron resonance spectrum, from single crystals of acid met myoglobin, have been measured in both 'high spin' and 'low spin' derivative form. The g-value variation is discussed in conjunction with the present structural knowledge of the myoglobin molecule obtained from X-ray measurements. Directions in the crystal, of importance in the electron resonance study are found to be closely parallel to features in the molecular structure. It is found that the direction of the maximum g-value in the azide derivative, which is also the direction of the crystalline electric field at the iron atom, makes an
angle of 9 degrees with the normal to the haem plane as calculated from electron resonance and X-ray measurements on the 'high spin' complex. This point is discussed in connection with a possible process whereby molecular groups may be exchanged at the such coordination point of the iron atom.
The line width variation of from 40 to 800 gauss has been explained in terms of a scatter in the orientation of the
principal g values, due to some form of disorder in the crystal structure. On this hypothesis, theoretical line width variations have been fitted to the experimentally observed line width variations. Values for the standard deviation in the orientation of the principal axes have been obtained in this way.