H. Appel

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.

The fate of implanted 19F ions in diamond and their theoretical modelling

Abstract The ubiquitous use of ion implantation and the simultaneous interest in the emplacement of selected impurities in the matrix of choice bring added emphasis to the need for a quantitative understanding of the residence sites adopted by such imputities. The time-dependent perturbed angular distribution technique has been used to study the case of fluorine implanted in diamond. Careful examination is presented of the dependence of the perturbation parameters on the characteristics of the implant sites. These comprehensive investigations reveal the power of the technique in the richness of detail exposed and make possible the theoretical modelling of the data.

Interpretation of perturbed angular distribution results for19F implanted into diamond

Perturbed Angular Distribution measurements have been made on natural diamond using recoil implanted fluorine ions as probes. Two distinct lattice sites for fluorine in diamond were found. Site identifications prompted by theoretical cluster calculations are presented. The PAD data are well described by a texture theory, though the origin of the texture effects is presently not known.

Influence of protein dynamics on the metal-sites of ovotransferrin.

Using the perturbed angular correlations (PAC) technique, the formation of hafnium-ovotransferrin complexes has been studied. Two binding configurations at each of the two specific binding-sites of the protein have been observed. They are characterized by well-defined electric quadrupole frequencies. Information about the dynamics of the protein was derived from temperature dependent measurements of the relaxation constant. The well-resolved spectra taken with fast BaF2-detectors allow a precise determination of the relaxation behaviour of the protein. The results are compared with the predictions from a hydrodynamic model for the reorientation of macromolecules. Thus the hydrodynamic volume of ovotransferrin and its N-terminal half-molecule were determined. The ovotransferrin volume is in agreement with a value derived for human serum transferrin from small angle neutron scattering. From experiments with immobilized protein material there is evidence for internal protein dynamics which is probed by the Hf-ion bound to the specific metal-sites.

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.

Temperature dependence of the electric field gradient parameters at 19F lattice sites in semiconducting and insulating diamonds

Abstract The electric field gradient parameters in insulating and semiconducting diamond, types IIa and IIb respectively, were measured as a function of temperature at residence sites of recoil implanted 19 F by using the time-dependent perturbed angular distribution nuclear solid state technique. An improved experimental arrangement enables three distinct residence sites to be resolved, where only two had been resolved before. These correspond to quadrupole coupling constants of 62(1), 56(2) and 31(3) MHz. A strong temperature dependence in the fractional population of the second site was observed and is different for each of the two types of diamond. These measurements provide additional evidence for the explanation of this temperature dependence, i.e. a charge transfer from the lattice to the 19 F occurs, which leads to the formation of the negative fluorine ion.

Hafnium binding to rat serum transferrin

Using the TDPAC-technique binding parameters for Hf were determined afterin vivo uptake of181Hf in rat plasma. As much as 98.5% of the metal ions proved to be bound to protein, essentially to transferrin. The main fraction of the181Hf ions experiences a well defined electric quadrupole perturbation frequency (vQ1=(1516 ± 15)MHz, δ1=(5.3 ± 0.8)%) connected with a marked relaxation damping (λ = (46 ± 8)MHz). The remaining Hf nuclei are subject to a fairly broad distribution of electric field gradients (vQ2=(1014 ± 37)MHz, δ2=(16±3)%). The results are compared with data obtained within vitro181Hf-labeled human transferrin.