Angular dependent rayleigh scattering of Mössbauer radiation on proteins

RSMR experiments with⁵⁷Fe radiation were performed on myoglobin. An areasensitive detector was employed for simultaneous angular dependent collection of the scattered quanta up to a maximum angle 2θ of 17‡. Experimental data of polycrystalline and lyophilized myoglobin are compared with computer calculations of the scattering which are based on the atomic coordinates determined by X-ray structure analysis. Special attention has been paid to the influence of coherence effects from collectively moving parts of the protein. A simple model is introduced in order to take into account these segmental motions. Our first results indicate that the sizes of collectively moving segments are comparable with spheres of about 6 å in diameter in dry myoglobin. In myoglobin crystals, where the molecules are surrounded by large hydration shells, the movements appear to be correlated in segments with sizes comparable to helices.

     

High-resolution time-of-flight system for precise measurement of excitation energies and Q-values

A time-of-flight system has been installed for the measurement of accelerator beam energies with an absolute accuracy of 1.5 : 10⁵ as proved by determining excitation energies in ⁶⁰Ni. The first $\text{T=}\text{3}\text{2}$ resonance in ¹²C(p,p)¹²C was measured at E_p=14230.75±0. 20 keV.     

The influence of the semiconductor properties on the Mössbauer emission spectra of 57Co cobalt oxide

⁵⁷CO_1?xO Mössbauer sources were prepared at 1000°C and different oxygen pressures. The number x of Co vacancies, which depend on the oxygen pressure during the preparation, determine the Fe³⁺ fraction in the emission spectrum of the source at room-temperature. A theoretical model allows a correlation between these quantities.Measurements on ⁵⁷Co_1?xO sources between room-temperature and 1000°C proved that at temperatures above 500°C electron relaxations between the ⁵⁷Fe^m impurity, introduced in the lattice as a consequence of the ⁵⁷Co decay, and the valence band take place. A theoretical model was developed which describes these relaxation phenomena reasonably well.     

Study of the104Ru(d,p)-reaction at 14 MeV

The reaction¹⁰⁴Ru(d, p) was investigated with high resolution (5 keV) at the Munich MP tandem using the Q3D spectrograph in conjunction with the precision time-of-flight system. The ground stateQ-value was determined as Q=3,684.5±1 keV. Proton spectra were measured at 7 angles in the range of 6.1°–65°. 19 levels could be identified in the excitation energy range 0–730 keV. Transferredl-values and spectroscopic factors of these levels were derived with the aid of DWBA calculations.     

Rayleigh scattering of Mössbauer radiation on a myoglobin single crystal

The RSMR technique was used to determine the fraction of radiation which is scattered elastically and inelastically, respectively, into Bragg reflections of a metmyoglobin single crystal. From this measurement 〈x² _1c〉=0.027±0.008 A² has been determined which is due to long range correlated motions in analogy to acoustic and optic modes in solids.     

Angular- and temperature-dependent RSMR on myoglobin using 183W and 57Fe

Myoglobin crystals are investigated by Rayleigh scattering of Mössbauer radiation at T = 87 K and T = 300 K and angles up to sin(?)/λ = 0.44 Å^?1. The results are analysed in terms of normal modes.     

Mössbauer Spectroscopy in the Energy and in the Time Domain,a Crucial Tool for the Investigation of Protein Dynamics

Hyperfine Interactions - New experiments on MbCO crystals and MbCO in a glycerol/water solution are described. Phonon-assisted Mössbauer effect reveals solid state like harmonic vibrations and...     

The sub-Coulomb197Au(t,d)198Au reaction

The influence of a deformation of the triton due to a non-s part of the ground state wave function on triton induced reactions is investigated. For this purpose, a measurement of the absolute cross section of the¹⁹⁷Au(t, d)¹⁹⁸Au reaction below 7 MeV was performed and compared with a finite range DWBA calculation. Implications on reactions with tritons during the primordial nucleosynthesis are briefly discussed.     

Synthesis of Unnatural Lipohilic N-(9H-Fluoren-9-ylmethoxy)carbonyl-Substituted α-Amino Acids and Their Incorporation into Cyclic RGD-Peptides: A structure-activity study

The α_v/β₃ integrin is implicated in human tumor metastasis and angiogenesis. It has been shown that structures of the sequence cyclo(-Arg¹-Gly²-Asp³-D -Phe⁴-Xaa⁵-) ( I ) and cyclo(-Arg¹-Gly²-Asp³-Phe⁴-D -Xaa⁵-) ( II ) bind with high affinity and the latter with high selectivity to this receptor. The residues Xaa and D -Xaa accept a broad variety of amino acids. Here, we report on the synthesis, activities, and conformational analysis of cyclic Arg-Gly-Asp (RGD) peptides containing liophilic amino acids Xaa or D -Xaa in position 5. For I , these were (2S)-2-aminohexadecanoic acid (Ahd) and N′-hexadecylglycine (Hd-Gly) and in II , D -Ahd and Hd-Gly, and, for control purposes, Ahd were incorporated (Fig. 1). The enantiomerically pure a-amino acids were obtained by non-enantioselective synthesis and subsequent enzymatic separation of isomers using acylase I (Scheme). Hd-Gly was prepared in a modified procedure according to Stewart from ethyl bromoacetate and hexadecylamine (Scheme). The synthesis and physicochemical properties of the corresponding (9H-fluoren-9-ylmethoxy)carbonyl (Fmoc) derivatives, compatible with solid-phase peptide synthesis, are described. Structure elucidation by NMR reveals that the lipid modification has no significant impact on the template structures when incorporated into them. For peptides I with Xaa = Ahd or Hd-Gly ( 1 or 2 ), a βII′/γ-turn-like arrangement with D -Phe in i+1 position of the β-turn is found. Peptides II with D -Xaa = D -Ahd or Hd-Gly ( 3 or 4 ) exhibit a βII′/γ-turn conformation with Gly in i+1 position of the β-turn, whereas II with Ahd instead of D -Xaa, i.e., lacking a D -amino acid in position 4 or 5 ( 5 ). adopts no defined conformation. However, in assays of receptor specificity employing human α_vv/β₃ integrin, the compounds exhibit IC₅₀ values ranging from nanomolar to less than millimolar. These results indicate that although the arrangement of the pharmacophoric groups is preserved in the target compounds, the biological activity is highly dependent on spatial requirements of the lipid anchor in the receptor binding pocket. Obviously, only certain positions do not affect the binding.