Electron resonance studies of haemoglobin derivatives III. Line-width and g -value measurements of acid-met myoglobin and of met myoglobin azide derivatives

Abstract

Details of the way in which haem plane orientations were deduced from g-value measurements on five different crystal types of acid-met myoglobin were given in parts I and II (Bennett, Gibson & Ingram 1957, and Bennett et al. 1961). This paper now summarizes more detailed measurements of line-width and g-value variations observed in both the acid-met and azide derivatives of type A myoglobin crystals. Since these crystals are those for which a detailed X-ray analysis is now available, a direct comparison of this with the electron resonance measurements can now be made. The g-values obtained for the azide derivative are first analysed, and their anisotropy and asymmetry are related to the possible orientation of the azide group itself. The line widths of the electron resonance absorptions, and their angular variations are then summarized and discussed. It is shown that their large magnitudes and rapid variation with angle can be explained in terms of a slight random misorientation of the molecular axes within the crystal, and that, due to the large g-value anisotropy in the acid-met derivative, a standard deviation of only 1.6 degrees in angular distribution is sufficient to explain the results obtained. A similar analysis is also applied to the results on the azide derivative.