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F Parak

Publications and source records attributed to F Parak.

49 records · Page 3Linked to original sources
PubMed1978

Subunit structure of Micrococcus luteus catalase. Dissociation of M. luteus catalase induced by dodecylsulfate, citraconic and 2,3-dimethylmaleic anhydrides and urea.

M. luteus catalase dissociates upon treatment with urea, dodecylsulfate and anhydrides into monomers, the molecular weight of which appears to be 1/4 of that of the native enzyme. The urea-induced dissociation depends upon the incubation time, the urea concentration and the pH of the incubation mixture. Reassociation of the subunits proved to be unsuccessful. Native M. luteus catalase only contains 30% alpha-helix. When fully dissociated in presence of urea, it still retains 15% alpha-helix. Catalase from M. luteus was found to lack cysteine residues.

Catalase↗
PubMed1977

Mössbauer and susceptibility experiments on different compounds of Fe3+-myoglobin.

The static magnetic susceptibilities of different ferric high spin and low spin compounds of myoglobin (Mb(H2O), Mb(H2O) frozen under high pressure, MbF, MbCN) were measured in the temperature region between 4.2 K and 130 K. Mössbauer absorption experiments on Mb(H2O) and MbF were performed at different temperatures between 4.2 K and 180 K and in small magnetizing fields H less than or equal to 1 kOe. The evaluation of our experimental data was performed with a Hamiltonian describing of 3d-configuration of the ferric iron by taking into account the Coulomb repulsion of the five electrons within the 3d-shell, the crystal electric field of C2v-symmetry, and the spine-orbit coupling. The Hamiltonian contains the splitting energies of the five antibonding d-orbitals (dxy, dx2, dy2, dx2-y2, dz2) as parameters. The values of these energies were obtained by a least squares fitting procedure using our magnetic susceptibility data together with the g-factors taken from the literature. In the case of MbF the energy difference between the two lowest Kramers doublets was also determined from present Mössbauer data. The results of the susceptibility and the Mössbauer data are in good agreement. The splitting energies of the 3d-orbitals can be correlated to the distances between the iron and its nearest neighbours. The different positions of the iron in the compounds investigated are discussed.

Cold Temperature↗
PubMed1977

Investigation of two deoxygenated haemoglobin-haptoglobin complexes by Mössbauer spectroscopy.

Haemoglobin Haptoglobin complexes formed when [Hp+]/[Hb]= 1/1 and [Hp]/[Hb] =2/1 were investigated by 57Fe Mössbauer spectroscopy. Both samples gave a spectrum consisting of a single quadrupole doublet. The temperature dependence of the quadrupole splitting was also identical for both samples. This proves that in both samples the nearest neighbour environment of the iron atom must be the same. A comparison with earlier investigations on myoglobin and haemoglobin indicates that the electronic structure of iron in the HbHp-complexes is similar to that in myoglobin.

Cold Temperature↗
PubMed1976

Investigation of the electronic term scheme of deoxygenated human haemoglobin by a least squares fit procedure using simultaneously magnetic susceptibility and Mössbauer data.

The calculation of the magnetic susceptibility from a published term scheme for the ferrous iron in deoxygenated human haemoglobin is discussed and a procedure for the simultaneous least squares fit of susceptibility and Mössbauer data is presented. The application of this procedure to the appropriate measurements on human haemoglobin leads to a rearrangement of the low lying electronic levels of the iron. The term schemes received as results of two different sets of susceptibility data used in combination with one set of Mössbauer data overlap with their error bars. The obtained level scheme of the Fe is correlated with the distance of the iron atom from the haem plane and the distance Fe-HIS F8, and some biological implications of these correlations are discussed.

Biophysics↗
PubMedDate not supplied

The active center of methemoglobin Hb(H2O) investigated by Mössbauer and susceptibility experiments.

A fast freezing technique using liquid propane was used to obtain frozen solutions of methemoglobin at pH 7. With this method it was possible to eliminate largely the presence of a low spin component which is usually found in slowly frozen solutions but not present in the sample at room temperature. The magnetic susceptibility and Mössbauer spectra of Hb(H2O) in the temperature range 4.2 K less than or equal to T less than or equal to 250 K have been measured. The data of the high spin compound of Hb(H2O) were evaluated with a Hamiltonian comtaining the Coulomb repulsion of the five 3d-electrons of the Fe3+ ion, a crystal electric field of C2V symmetry and the spin orbit coupling. The term describing the crystal electric field depends on five energy parameters epsilon1, epsilon2, epsilon3, D, and E which are determined by least squares fits to the experimental data. The most relevant parameters epsilon 2 and epsilon 3 which equal the energies of the antibonding single 3d-electron orbitals 3dz2 and 3dx2-y2 with respect to the 3dxy orbital are compared with earlier results of these energies epsilon 2 and epsilon 3 of the high spin compound of Mb(H2O). From this comparison conclusions regarding the different spatial arrangements of Fe3+ in Hb(H2O) and Mb(H2O) are drawn.

Binding Sites↗
PubMedDate not supplied

The orientation of the electric field gradient tensor in CO-liganded myoglobin.

The EFG-tensor at the position of the Fe-atom of CO-liganded sperm whale myoglobin has been investigated by nuclear gamma-resonance absorption experiments on single crystals. In addition the temperature dependence of the quadrupole splitting of the 14.4 keV level of the iron nucleus was measured. An unambiguous solution for the magnitude and the orientation of the field gradient tensor could only be obtained with the assumption that a C2-axis perpendicular to the haem plane is one principal axis of the electric field gradient tensor. Within this solution the electronic structure of the iron is described by a singlet ground state with Nz = 0.75 and the largest EFG component perpendicular to the haem plane.

Animals↗
PubMedDate not supplied

Mössbauer spectroscopy on oxygenated sperm whale myoglobin: evidence for an Fe3+-O2- coupling at the active center.

57Fe Mössbauer spectra of oxygenated sperm whale myoglobin (MbO2) show a well resolved quadrupole doublet with a temperature dependent splitting. The temperature dependence of the corresponding electric field gradient tensor (EFG) can be calculated from a Fe3+ term scheme for the iron at the active center. The Mössbauer spectra as well as the diamagnetc character of the MbO2-complex are then understood by an exchange coupling of the Fe3+-ion with O2- oxygen molecule ion. The resulting groundstate is a diamagnetic singlet. In order to keep the whole complex diamagnetic at room temperature, an exchange coupling with [J] greater than or equal to 300cm-1 is necessary. As the whole model is in fair agreement with many other spectroscopic data, it is believed to be a good starting point for further detailed calculations.

Animals↗
PubMedDate not supplied

Investigation of large intramolecular movement within metmyoglobin by Rayleigh scattering of Mössbauer radiation (RSMR).

This paper reports Rayleigh scattering experiments on metmyoglobin crystals and freeze dried myoglobin which was exposed to air with different parital pressure of water vapor. While dry myoglobin shows no fluctuations between conformational substates such "breathing modes" are rarely seen in water covered myoglobin. Larger amounts of water increase the average mean square displacements. In crystals the dynamic behaviour is hindered by the crystal packing. The results are analysed by a theory describing the motion within the molecule by a Langevin equation with restoring forces corresponding to a square well potential.

Animals↗
PubMedDate not supplied

[Polychromatic kinetics of conformational and spin relaxation of reduced intermediates of myoglobin].

Moessbauer spectroscopy was used to study the relaxation of a non-equilibrium myoglobin state produced at 77 K by reduction of metmyoglobin Fe(III) with thermalized electrons. The intermediate is characterized with the metMb (r) conformation of the protein globule and a low spin heme Fe(II) with a water molecule on the sixth coordination site. The intermediate is stable at 77 K but relaxes with increasing temperature into equilibrium deoxymyoglobin with dissociation of the bond Fe(II)-H2O and the transition of the Iron into the high spin state. In the temperature range 147-195 K the relaxation kinetics is nonexponential in time and can be described in terms of the polychromatic kinetics. A fitting of the kinetics data supposing a gamma-distribution of activation enthalpies of the relaxation shows a shift and a narrowing of the distribution at T > 180 K. The effect of structural rearrangements and equilibrium conformational fluctuations in the protein on the shape of the observed barrier distribution is discussed.

Animals↗