K. Matlak

The dynamics of the non-heme iron in bacterial reaction centers from Rhodobacter sphaeroides.

We investigate the dynamical properties of the non-heme iron (NHFe) in His-tagged photosynthetic bacterial reaction centers (RCs) isolated from Rhodobacter (Rb.) sphaeroides. Mössbauer spectroscopy and nuclear inelastic scattering of synchrotron radiation (NIS) were applied to monitor the arrangement and flexibility of the NHFe binding site. In His-tagged RCs, NHFe was stabilized only in a high spin ferrous state. Its hyperfine parameters (IS=1.06±0.01mm/s and QS=2.12±0.01mm/s), and Debye temperature (θ(D0)~167K) are comparable to those detected for the high spin state of NHFe in non-His-tagged RCs. For the first time, pure vibrational modes characteristic of NHFe in a high spin ferrous state are revealed. The vibrational density of states (DOS) shows some maxima between 22 and 33meV, 33 and 42meV, and 53 and 60meV and a very sharp one at 44.5meV. In addition, we observe a large contribution of vibrational modes at low energies. This iron atom is directly connected to the protein matrix via all its ligands, and it is therefore extremely sensitive to the collective motions of the RC protein core. A comparison of the DOS spectra of His-tagged and non-His-tagged RCs from Rb. sphaeroides shows that in the latter case the spectrum was overlapped by the vibrations of the heme iron of residual cytochrome c(2), and a low spin state of NHFe in addition to its high spin one. This enabled us to pin-point vibrations characteristic for the low spin state of NHFe.

The influence of very small doses of alpha radiation on the stability of erythrocytes

Our aim was to study the influence of low doses (0.2–4 μGy) of α radiation on the stability of human erythrocytes isolated from healthy and diabetic erythrocytes. Absorption spectroscopy was used to measure the level of red blood cell (RBC) hemolysis, along with Mössbauer spectroscopy, which is a highly specific method suited to monitoring various hemoglobin forms. States of hemoglobin are sensitive to a homeostatic imbalance in red blood cells. Changes in the membrane skeleton organization of irradiated erythrocytes isolated from healthy donors were studied using atomic force microscopy (AFM). Hemolysis, in healthy red blood cells, showed characteristic discontinuities, depending on the α particle flux and the exposure time to the low doses applied. This phenomenon was not observed in severe diabetic cases, which could be a result of modified protein–lipid–sugar complexes and the attenuation/absence of some antioxidative enzymatic processes in their RBC membranes. Similar effects were also observed for red blood cells treated with low doses of neutron and γ‐radiation. AFM measurements demonstrated a reorganization of the RBC membrane skeleton network depending on the time of RBC exposure to α radiation. This suggests that the changes in the activity of the acute defense processes against free radicals which are activated within the erythrocyte membrane irradiated with α‐particles could additionally be up‐ or down regulated by modifications to the membrane–skeleton network. However, even the highest dose of α radiation applied in these studies did not cause any significant changes in the ability of hemoglobin to transport oxygen. Microsc. Res. Tech. 80:131–143, 2017.

Influence of Cd2+ on the spin state of non-heme iron and on protein local motions in reactions centers from purple photosynthetic bacterium Rhodospirilium rubrum

Non-heme Fe is a conservative component of the Q-type photosynthetic reaction centers but its function remains unknown. Applying Mossbauer spectroscopy we show that in Rhodospirillum rubrum the non-heme Fe exists mostly in a ferrous low spin state. The binding of Cd2+ ions in the vicinity of the quinone-Fe complex changes the high spin state of the non-heme Fe into a low spin one characterized by hyperfine parameters similar to those obtained for the non-heme Fe low spin state in untreated reaction centers, as confirmed by Mossbauer measurements. The nuclear inelastic scattering of synchrotron radiation experiments show that the contribution of vibrations at low energies, between 3-15 meV, activated at 240 K are damped in the bacterial reaction centers treated with CdCl2. No influence of Cd2+ ions is observed on the soft vibrational states at 60 K. These results suggest that binding of cadmium cations within the reaction centers may enhance decoupling of the non-heme Fe from the surrounding protein matrix at temperatures higher than 200 K, what can explain the slowing down of electron transfer between the QA and QB quinones by Cd2+.

Magnetism of ultra-thin iron films seen by the nuclear resonant scattering of synchrotron radiation

Conversion electron Mossbauer spectroscopy proved in the past to be very useful in studying surface and ultrathin film magnetism with monolayer resolution. Twenty years later, its time-domain analogue, the nuclear resonant scattering (NRS) of synchrotron radiation, showed up to be by orders of magnitude faster and more efficient. The evolution of the spin structure in epitaxial 57Fe films on a tungsten W(110) was studied via the accumulation of the NRS time spectra directly during Fe film deposition. In the 0.5 – 4 monolayers Fe thickness range, the complex non-collinear magnetic structure was derived from the NRS data, resulting from the deviation from the layer by layer growth mode. For thicker Fe films, the in-plane thickness induced spin reorientation transition could be clearly identified. Based on the NRS analysis it is shown that SRT process originates at the Fe/W(110) interface and proceeds through a transient fan-like magnetization structure.