A THEORETICAL-ANALYSIS OF THE H-1 NUCLEAR MAGNETIC-RELAXATION DISPERSION PROFILES OF DIFERRIC TRANSFERRIN

The magnetic field dependence of water proton relaxation rates of dife rric transferrin solutions has been analyzed over the 0.01-200-MHz ran ge. There is evidence of both fast and slow exchanging protons. The fo rmer provide the shape of the proton relaxation rate profile. The effe ct of ZFS and its disappearance when the Zeeman energy dominates the Z FS provide an inflection in the nuclear relaxation dispersion profile around 10 MHz. The experimental profiles can be quantitatively interpr eted by taking into account (i) a rhombic ZFS of the iron(III) ions, ( ii) the change of the quantization axes along which the electron relax ation rates are defined on passing from the ZFS limit to the Zeeman li mit, and (iii) the usual Zeeman limit field dependence of the electron relaxation rates.