Determination of the principal axes of the magnetic susceptibility tensor for horse heart oxidized cytochrome c in solution

Abstract

The magnetic axes in horse heart oxidized cytochrome c were calculated by magnetic anisotropy tensor determination utilizing the haem methyls (MATDUHM) and were compared with those calculated by the conventional least-squares search method (LSSM). For the backbone C_αH proton resonances, the calculated shifts using the LSSM axes correlate better with the observed shifts, i.e. the chemical shift difference between the resonances of the reduced and oxidized forms, than those using the MATDUHM axes. The correlation for the backbone NH proton resonances is almost comparable for the two sets of axes. Therefore the validity of MATDUHM was confirmed. Since the applicability of LSSM is limited to haemoproteins for which the crystal structures are known, MATDUHM is the only method so far available that can be applied to any iron(III) low-spin haemoproteins under various solution conditions to locate the magnetic axes.