Harman's theory of aging proposes that a buildup of damaging reactive oxygen species (ROS) is one of the primary causes of the deleterious symptoms attributed to aging. Cellular defenses in the form of antioxidants have evolved to combat ROS and reverse damage; one such group is the methionine sulfoxide reductases (Msr), which function to reduce oxidized methionine. MsrA reduces the S enantiomer of methionine sulfoxide, Met-S-(o), while MsrB reduces the R enantiomer, Met-R-(o). The focus of this study was to investigate how the absence of one or both forms of Msr affects locomotion in Drosophila using both traditional genetic mutants and more recently developed RNA interference (RNAi) strains. Results indicate that lack of MsrA does not affect locomotion. However, lack of MsrB drastically reduces rates of locomotion in all age classes. Furthermore, creation of an RNAi line capable of knocking down both MsrA and MsrB in progeny was completed. / by Kori Mulholland. / Thesis (M.S.)--Florida Atlantic University, 2013. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

Aging is a multifactoral biological process of progressive and deleterious changes partially attributed to a build up of oxidatively damaged biomolecules resulting from attacks by free radicals. Methionine sulfoxide reductases (Msrs) are enzymes that repair oxidized methionine (Met) residues found in proteins. Oxidized Met produces two enantiomers, Met-S-(o) and Met-R-(o), reduced by MsrA and MsrB respectively. Unlike other model organisms, our MsrA null fly mutant did not display increased sensitivity to oxidative stress or shortened lifespan, suggesting that in Drosophila, having either a functional copy of either Msr is sufficient. Here, two Msr mutant types were phenotypically assayed against isogenic controls. Results suggest that only the loss of both MsrA and MsrB produces increased sensitivity to oxidative stress and shortened lifespan, while locomotor defects became more severe with the full Msr knockout fly. / by Kelli Robbins. / Thesis (M.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 164-177).

The processes that control the reductive dissolution of Mn0₂ by Fe(II) under conditions simulating the effects of acid mine drainage on subsurface environments and the subsequent precipitation of Fe(III) has been investigated. Results from real-time, in situ X-ray absorption spectroscopy (XAS) flow-through reaction cell studies indicate that a mixed Fe/Mn solid phase with the local structure of the spinel mineral jacobsite (MnFe₂O₄) is formed after the Mn0₂ surfaces are coated with ferric precipitates. In the absence of previously precipitated Fe(III), no reduced manganese solid is formed. The ferric precipitates do not incorporate significant quantities of Mn(II) down gradient from the reactive Fe(II) front. The maximum amount of the original Mn0₂ incorporated into this jacobsite-like solid is 5%. Results from batch experiments showed similar results compared to the flow-through experiments, with an initially fast rate of Mn(II) release, followed by a much slower release after 5-10 min had elapsed. The reaction products, Fe(III)(aq) and Fe(III)(s) were found to decrease the initial reaction rate. A simple model was developed to describe the temporal concentrations of Mn(II)(aq), Fe(II)(aq), and Fe(III)(aq) that include a Langmurian blocking function to describe the effects of the ferric reaction products on the reaction rate. The model also allowed for a second order process to occur at long time that was dependent solely on the aqueous concentrations of Fe(II) and Mn02. The formation of the ferric reaction products were found to transform from aqueous sulfate complexes to (presumable) ternary surface complexes with sulfate. Within 10 h, these precipitates may have formed chains of edge-sharing octahedra on the order of 60 Å. The precipitates have large amount of sulfate associated with them, which may preclude the formation of ferrihydrite, and may indicate the formation of schwertmannite. The average Fe:SO₄ ratio was 4.4 ± 1.0, a value similar to that reported for schwertmannite. The presence of goethite was identified by X-ray diffraction as early as 50 d, indicating that sulfate is being excluded from the precipitates. The release of Mn(II), FeT, and sulfate was controlled by diffusion, which may also be the process that controls the rate of transformation.

Photosystem II (PSII) is the membrane-bound oxidoreductase peptide complex responsible for the oxidation of water to molecular oxygen and reduction of plastoquinone to plastoquinol. Primary electron transfer is initiated upon absorption of a photon by the primary donor chl resulting in electron transfer and production of a P680+QA charge separated state. P680+ is reduced by YZ (Y161 of the D1 polypeptide subunit), one of two redox-active tyrosine residues found in PSII. This produces a neutral tyrosyl radical (YZ ) which is subsequently reduced by electrons derived from water at the oxygen-evolving complex (OEC). The OEC is composed of four manganese, one calcium ion, and one chloride ion. Four photons are required to convert water to O2, each photon advancing the OEC through successive oxidation states or S states. The exact chemical mechanism of water oxidation in PSII is not known. However, proton-coupled electron transfer (PCET) is thought to be one of the fundamental steps in driving the extraction of electrons and protons from water. Here, the mechanism of water oxidation is investigated with focus on PCET events using vibrational spectroscopy. Vibrational spectroscopy is sensitive to changes in protein structure, charge, and hydrogen bonding, and is ideal for the study of fast events coupled with light-induced electron transfer. The results presented here demonstrate the utility of time-resolved infrared spectroscopy in the detection of intermediates of photosynthetic water oxidation. We suggest that proton transfer may precede manganese oxidation during water oxidation based on time-resolved infrared and difference FT-IR spectroscopic results. The mechanism of PCET associated with YZ reduction is investigated. Using reaction-induced difference FT-IR spectroscopy, the identity of the chloride binding site is speculated through the use of bromide exchange at the OEC. Also, proton transfer reactions at the OEC are investigated using azide as a vibrational probe. The advances in the understanding of photosynthetic water oxidation gained in this work will aid in the elucidation of the chemical mechanism of this important reaction. Understanding the details of photosynthetic water oxidation will assist in the development of technology aimed at harnessing the energy of the sun for the benefit of humankind.

Dissertation (Ph.D.)--University of South Florida, 2007. / Title from PDF of title page. Document formatted into pages; contains 197 pages. Includes vita. Includes bibliographical references.

Dissertation (Ph.D.)--University of South Florida, 2007. / Includes vita. Includes bibliographical references (leaves 188-197). Also available online.

Thesis (Ph.D. in Pharmaceutical Sciences) -- University of Colorado Denver, 2008. / Typescript. Includes bibliographical references (leaves 219-242). Free to UCD affiliates. Online version available via ProQuest Digital Dissertations;

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 164-174).

Thesis (Ph.D. in Pharmaceutical Sciences) -- University of Colorado Denver, 2007. / Typescript. Includes bibliographical references (leaves 133-143). Online version available via ProQuest Digital Dissertations.