W. G. Thies

X-ray solution scattering reveals conformational changes upon iron uptake in lactoferrin, serum and ovo-transferrins.

X-ray solution scattering has been used for studying the structural changes that take place upon uptake and release of iron from serum and chicken ovo-transferrin and human lactoferrin. In the case of chicken ovo-transferrin, data have been obtained for both the intact protein and the isolated N and C-lobes with and without iron. These studies reveal that both lobes undergo a change that is consistent with an opening of the inter-domain cleft when iron is removed from the protein. We suggest that the conformational change of the protein increases the specificity of receptor binding and that the closed configuration of the iron-loaded protein is one, or perhaps the, decisive step in the mechanism for receptor-mediated endocytosis.

Temperature dependence of the electric field gradient in HfF4.HF.2H2O

The hyperfine quadrupole interaction in HfF4.HF.2H2O was studied using the time differential perturbed angular correlation (TDPAC) technique. The electric field gradient (EFG) and the corresponding asymmetry parameter were measured in the temperature range from 9 to 350 K. The EFG is characterized by a rather strong increase with temperature, whereas the asymmetry parameter reaches its maximum value (η≈1) at aboutT=160 K. At 420 K, the complex is dehydrated and looses HF: The quadrupole parameters determined from subsequent TDPAC measurements are charateristic for HfF4.

TDPAC studies on181Hf implanted into diamond

Abstract19F has been used to probe the electric field gradients in the diamond lattice. The measurements were performed via the time differential perturbed angular distribution (TDPAD) technique applied to the 197 keV state (τ=128 ns, Q=0.10 b) of19F. The nuclei were excited and recoil implanted into the diamond crystal using a (p,p′γ)-reaction initiated by a pulsed 4 MeV proton beam. Spin rotation spectra were generated to study the dependence of the electric field gradients on the orientation of the crystal planes, the diamond type, and temperature.

High resolution181Hf TDPAC spectroscopy using fast BaF2-detectors

A high resolution TDPAC setup with four BaF2 detectors was introduced for measurements in chemical and biological systems. High electric field gradients and large asymmetry parameters could be determined very precisely. The data are compared to previous NaI(Tl) measurements on HfF4·HF·2H2O, HfO2, and181Hf-labelled transferrin.

Evidence of internal protein dynamics in transferrins from TDPAC experiments

The relaxation in liquid transferrin and ovotransferrin samples has been studied at different temperatures using the TDPAC method. Information about reorientation and internal dynamics has been obtained from immobilized protein samples. Characteristic differences between the two proteins will be discussed.

TDPAC STUDIES OF THE IRON-MOLYBDENUM COFACTOR IN NITROGENASE

The uptake and the processing of molybdenum in nitrogen fixing bacteria was studied applying the TDPAC-technique with radioactive 99Mo. The observation of the nuclear quadrupole frequencies allowed a ‘finger-printing’ of the characteristic binding states in three bacteria species. The measurements have been carried out with intact cells and with the isolated proteins. In one bacterium a molybdenum storage protein was identified.

Hafnium binding to comparison: comparison between lactoferrin and other transferrins

The TDPAC method was used to study the electric field gradients at the metal sites of human and bovine lactoferrin. Two specific binding configurations were observed. The distribution between these configurations depends on the phosphate content, the pH, and the temperature of the samples. The electric field gradients are compared with the results of previous studies for human and rat serum transferrin, and hen ovotransferrin.

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.