Perturbed angular correlation studies of the metal-binding sites in ovotransferrin and its C- and N-terminal halves

The perturbed angular correlation (PAC) technique has been applied to study the electric quadrupole interaction of 181Hf nuclei at the binding sites of ovotransferrin (OTF) molecules. Two specific electric field gradients were observed. Their relative intensities depend on the pH value and the temperature of the samples, whereas the electric quadrupole interaction parameters themselves remain unaffected. In order to compare the binding sites in OTF, experiments with N- and C-terminal half-molecules were performed. Both specific configurations are observed at the N-terminal and at the C-terminal binding site with similar quadrupole parameters as for the intact protein. Remarkably, the stability of the hafnium binding to the C-terminal fragment appears to be reduced as compared with the N-terminal half and the intact protein.