Browsing by Subject "Mossbauer"
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Item Investigating the Roles of Vacuoles in Iron Trafficking in Saccharomyces cerevisiae(2013-11-27) Cockrell, Allison LeighTransition metals play essential roles in biological systems, but Fe can also be toxic to cells. In order to maintain this balance between necessity and toxicity mechanisms are employed for regulating and storing intracellular Fe. In Saccharomyces cerevisiae, vacuoles are responsible for sequestering, storing, and supplying Fe to the cytosol. Many of the proteins and regulatory pathways involved in Fe trafficking and storage in S. cerevisiae have been identified, but the forms of Fe which are involved in these processes have not been fully characterized. In these studies, biophysical and bioanalytical techniques were used to study intracellular Fe distributions in S. cerevisiae cells and organelles. Ultimately, Fe-containing species were biophysically characterized and absolute Fe concentrations in cells and organelles were quantified. The motivation for these studies stemmed from previous studies which revealed that the majority of the whole-cell Fe is a non-heme, high-spin (NHHS) form of Fe^(3+). This Fe is not localized to the mitochondria. The purpose of these studies was to determine if the vacuoles contained this NHHS Fe^(3+). A large-scale isolation procedure was developed to obtain purified vacuoles from S. cerevisiae and to investigate the Fe in these organelles. M?ssbauer and EPR analysis revealed that the primary form of Fe in vacuoles is a mononuclear, NHHS Fe^(3+) species. A second form of Fe was also observed as superparamagnetic ferric phosphate nanoparticles (NP). By investigating model compounds of Fe and polyphosphate we determined that a shift in vacuolar pH induces the conversion between NHHS Fe^(3+) and NP. These results showed that there are at least two forms of Fe in vacuoles, and that the ratio of these two forms is dependent upon the pH of these organelles. Biophysical analyses of whole cells also revealed the presence of low concentrations of a non-heme, high-spin Fe^(2+) species. The goal of these next projects was to determine if this NHHS Fe^(2+) species was localized to the cytosol. Genetic strains lacking or over-expressing the vacuolar Fe import protein Ccc1p were studied by M?ssbauer spectroscopy (?CCC1 and CCC1-up, respectively). ?CCC1 cells showed low vacuolar Fe (NHHS Fe3+ and NP), and increased NHHS Fe^(2+). We hypothesize that this NHHS Fe^(2+) is cytosolic Fe. We also propose that this NHHS Fe^(2+) is involved in the regulating intracellular Fe levels. CCC1-up cells accumulated more Fe than wild-type (WT) cells, and showed elevated levels of vacuolar Fe (NHHS Fe^(3+) and NP). These cells also accumulated high levels of NHHS Fe^(2+). The CCC1-up cells exhibited an adenine deficient phenotype, where the cells developed a red color during growth. With excess adenine the levels of NHHS Fe^(2+) declined, which indicated that this Fe accumulation was related to adenine deficiency. We conclude that adenine deficiency leads to the accumulation of a sequestered (possibly vacuolar) form of NHHS Fe^(2+). Overall, we have identified two separate pools of NHHS Fe^(2+) in ?CCC1 and CCC1-up cells. In ?CCC1 cells the NHHS Fe^(2+) pool is localized to the cytosol and is sensed by the cell. In CCC1-up cells the NHHS Fe^(2+) is sequestered from the Fe regulatory mechanism- possibly in the vacuoles. These data have helped us better understand the roles of vacuoles in Fe trafficking and the dynamics of vacuolar Fe trafficking.Item Optical control of nuclear resonant absorption: theory and experiment(Texas A&M University, 2004-09-30) Kolesov, Roman L.Modification of nuclear resonant absorption by means of laser radiation is analyzed both theoretically and experimentally. Theoretical analysis is done on the basis of four-level model of atom. This model includes both electronic and nuclear excitations. It is predicted that under coherent laser driving nuclear resonant Mossbauer absorption can be significantly modified, e.g. new Mossbauer resonances can appear, some of the existing resonances can vanish, both can be Rabi-split, broadened by laser action. In addition, it is predicted that Mossbauer absorption can be completely suppressed due to coherent population trapping. Experimental observation of laser-induced transformations of Mossbauer spectra of 57Fe2+ : MgO is accomplished. New Mossbauer lines appear with laser driving while the existing are broadened. Possible explanations of the observed changes in 57Fe2+ : MgO Mossbauer spectra are population of higher-lying electronic states of iron ion and significant modification of electronic relaxation processes due to modified Jahn-Teller interaction.Item Quantum coherence phenomena in x-ray optics(2009-05-15) Anisimov, Petr MikhailovichThe effects of quantum coherence in X-ray optics at nuclear transitions are investigated from a theoretical point of view. First, we introduce the general concept of the decaying dressed states and present a classification of the quantum coherence effects in a three-level coherently driven system. Second, we show that the interference effects may appear in X-ray radiation at the nuclear transitions under the condition of the nuclear level anti-crossing. This effects are similar to electromagnetically induced transparency, which has been widely studied earlier at the electronic transitions in optics. We also suggest a new technique for inhomogeneous line narrowing at nuclear transitions. This technique is based on the combined action of RF and DC fields and adopted to be applied in the M?ossbauer spectroscopy. Numerical simulation of a simple model with the dipole-dipole interaction is presented in order to demonstrate the efficiency of the technique. Finally, we study the possibility to suppress the nuclear elastic forward scattering in the synchrotron experiments using trains of pulses. A numerical model is developed to confirm this possibility and the main issue of relative phases of consecutive pulses is discussed.