PERTURBED-ANGULAR-CORRELATION STUDIES OF THE METAL-BINDING SITES IN OVOTRANSFERRIN AND ITS C-TERMINAL AND N-TERMINAL HALVES

The perturbed angular correlation (PAC) technique has been applied to study the electric quadrupole interaction of Hf-181 nuclei at the bind ing sites of ovotransferrin (OTF) molecules. Two specific electric fie ld gradients were observed. Their relative intensities depend on the p H value and the temperature of the samples, whereas the electric quadr upole 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 observ ed at the N-terminal and at the C-terminal binding site with similar q uadrupole parameters as for the intact protein. Remarkably, the stabil ity of the hafnium binding to the C-terminal fragment appears to be re duced as compared with the N-terminal half and the intact protein.