Matching Items (5)
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- All Subjects: Electron transfer
- All Subjects: Quinone
- Creators: Rose, Seth
- Creators: Redding, Kevin E
Description
Mitochondria produce most of the ATP needed for the cell as an energy source. It is well known that cellular respiration results in oxidative damage to the cell due to the production of reactive oxygen species (ROS). Mitochondrial dysfunction is believed to contribute to a number of degenerative diseases; because of this the mitochondrial respiratory chain is considered as potential drug target. A few series of idebenone analogues with quinone, pyridinol and pyrimidinol redox cores have been synthesized and evaluated as antioxidants able to protect cellular integrity and, more specifically, mitochondrial function. The compounds exhibited a range of activities. The activities observed were used for the design of analogues with enhanced properties as antioxidants. Compounds were identified which provide better protection against oxidative stress than idebenone, and it is thought that they do so catalytically.
ContributorsArce Amezquita, Pablo M (Author) / Hecht, Sidney M. (Thesis advisor) / Moore, Ana (Committee member) / Rose, Seth (Committee member) / Arizona State University (Publisher)
Created2012
Description
Photosystem I (PSI) is a multi-subunit, pigment-protein complex that catalyzes light-driven electron transfer (ET) in its bi-branched reaction center (RC). Recently it was suggested that the initial charge separation (CS) event can take place independently within each ec2/ec3 chlorophyll pair. In order to improve our understanding of this phenomenon, we have generated new mutations in the PsaA and PsaB subunits near the electron transfer cofactor 2 (ec2 chlorophyll). PsaA-Asn604 accepts a hydrogen bond from the water molecule that is the axial ligand of ec2B and the case is similar for PsaB-Asn591 and ec2A. The second set of targeted sites was PsaA-Ala684 and PsaB-Ala664, whose methyl groups are present near ec2A and ec2B, respectively. We generated a number of mutants by targeting the selected protein residues. These mutations were expected to alter the energetics of the primary charge separation event.
The PsaA-A684N mutants exhibited increased ET on the B-branch as compared to the A-branch in both in vivo and in vitro conditions. The transient electron paramagnetic resonance (EPR) spectroscopy revealed the formation of increased B-side radical pair (RP) at ambient and cryogenic temperatures. The ultrafast transient absorption spectroscopy and fluorescence decay measurement of the PsaA-A684N and PsaB-A664N showed a slight deceleration of energy trapping. Thus making mutations near ec2 on each branch resulted into modulation of the charge separation process. In the second set of mutants, where ec2 cofactor was target by substitution of PsaA-Asn604 or PsaB-Asn591 to other amino acids, a drop in energy trapping was observed. The quantum yield of CS decreases in Asn to Leu and His mutants on the respective branch. The P700 triplet state was not observed at room and cryogenic temperature for these mutants, nor was a rapid decay of P700+ in the nanosecond timescale, indicating that the mutations do not cause a blockage of electron transfer from the ec3 Chl. Time-resolved fluorescence results showed a decrease in the lifetime of the energy trapping. We interpret this decrease in lifetime as a new channel of excitation energy decay, in which the untrapped energy dissipates as heat through a fast internal conversion process. Thus, a variety of spectroscopic measurements of PSI with point mutations near the ec2 cofactor further support that the ec2 cofactor is involved in energy trapping process.
The PsaA-A684N mutants exhibited increased ET on the B-branch as compared to the A-branch in both in vivo and in vitro conditions. The transient electron paramagnetic resonance (EPR) spectroscopy revealed the formation of increased B-side radical pair (RP) at ambient and cryogenic temperatures. The ultrafast transient absorption spectroscopy and fluorescence decay measurement of the PsaA-A684N and PsaB-A664N showed a slight deceleration of energy trapping. Thus making mutations near ec2 on each branch resulted into modulation of the charge separation process. In the second set of mutants, where ec2 cofactor was target by substitution of PsaA-Asn604 or PsaB-Asn591 to other amino acids, a drop in energy trapping was observed. The quantum yield of CS decreases in Asn to Leu and His mutants on the respective branch. The P700 triplet state was not observed at room and cryogenic temperature for these mutants, nor was a rapid decay of P700+ in the nanosecond timescale, indicating that the mutations do not cause a blockage of electron transfer from the ec3 Chl. Time-resolved fluorescence results showed a decrease in the lifetime of the energy trapping. We interpret this decrease in lifetime as a new channel of excitation energy decay, in which the untrapped energy dissipates as heat through a fast internal conversion process. Thus, a variety of spectroscopic measurements of PSI with point mutations near the ec2 cofactor further support that the ec2 cofactor is involved in energy trapping process.
ContributorsBadshah, Syed Lal (Author) / Redding, Kevin E (Thesis advisor) / Fromme, Petra (Committee member) / Gould, Ian (Committee member) / Arizona State University (Publisher)
Created2014
Description
Photochromic molecules, which photoisomerize between two chemically and optically distinct states, are well suited for electron and energy transfer to covalently attached chromophores. This dissertation aims to manipulate electron and energy transfer by photochromic control in a number of organic molecular systems. Herein the synthesis, characterization and function of these organic molecular systems will be described. Electron and energy transfer were quantified by the use of steady state absorbance and fluorescence, as well as time-resolved fluorescence and transient absorbance. A dithienylethene-porphrin-fullerene triad was synthesized to investigate photochromic control of photo-induced electron transfer. Control of two distinct electron transfer pathways was achieved by photochromic switching. A molecular dyad was synthesized, in which fluorescence was modulated by energy transfer by photoinduced isomerization. Also described is a triplet-triplet annihilation upconversion system that covalently attaches fluorophores to improve quantum yield. Overall these studies demonstrate complex molecular switching systems, which may lead to advancement in organic electronic applications and organic based artificial photosynthesis systems.
ContributorsCrisman, Jeffrey (Author) / Gust, John D (Thesis advisor) / Rose, Seth (Committee member) / Moore, Ana (Committee member) / Arizona State University (Publisher)
Created2014
Description
To mimic the membrane environment for the photosynthetic reaction center of the photoheterotrophic Heliobacterium modesticaldum, a proteoliposome system was developed using the lipids found in native membranes, as well as a lipid possessing a Ni(II)-NTA head group. The liposomes were also saturated with menaquinone-9 to provide further native conditions, given that menaquinone is active within the heliobacterial reaction center in some way. Purified heliobacterial reaction center was reconstituted into the liposomes and a recombinant cytochrome c553 was decorated onto the liposome surface. The native lipid-attachment sequence of cytochrome c553 was truncated and replaced with a hexahistidine tag. Thus, the membrane-anchoring observed in vivo was simulated through the histidine tag of the recombinant cytochrome binding to the Ni(II)-NTA lipid's head group. The kinetics of electron transfer in this system was measured and compared to native membranes using transient absorption spectroscopy. The preferential-orientation of reconstituted heliobacterial reaction center was also measured by monitoring the proteoliposome system's ability to reduce a soluble acceptor, flavodoxin, in both whole and detergent-solubilized proteoliposome conditions. These data demonstrate that this proteoliposome system is reliable, biomimetic, and efficient for selectively testing the function of the photosynthetic reaction center of Heliobacterium modesticaldum and its interactions with both donors and acceptors. The recombinant cytochrome c553 performs similarly to native cytochrome c553 in heliobacterial membranes. These data also support the hypothesis that the orientation of the reconstituted reaction center is inherently selective for its bacteriochlorophyll special pair directed to the outer-leaflet of the liposome.
ContributorsJohnson, William Alexander (Author) / Redding, Kevin E (Thesis advisor) / Van Horn, Wade D (Committee member) / Jones, Anne K (Committee member) / Arizona State University (Publisher)
Created2018
Description
Healthy mitochondria are essential for cell survival. Described herein is the synthesis of a family of novel aminoquinone antioxidants designed to alleviate oxidative stress and prevent the impairment of cellular function. In addition, a library of bleomycin disaccharide analogues has also been synthesized to better probe the tumor targeting properties of bleomycin. The first study involves the synthesis of a benzoquinone natural product and analogues that closely resemble the redox core of the natural product geldanamycin. The synthesized 5-amino-3-tridecyl-1,4-benzoquinone antioxidants were tested for their ability to protect Friedreich's ataxia (FRDA) lymphocytes from induced oxidative stress. Some of the analogues synthesized conferred cytoprotection in a dose-dependent manner in FRDA lymphocytes at micromolar concentrations. The biological assays suggest that the modification of the 2-hydroxyl and N-(3-carboxypropyl) groups in the natural product can improve its antioxidant activity and significantly enhance its ability to protect mitochondrial function under conditions of oxidative stress. The second project focused on the synthesis of a library of bleomycin disaccharide-dye conjugates and monitored their cellular uptake by fluorescence microscopy. The studies reveal that the position of the carbamoyl group plays an important role in modulating the cellular uptake of the disaccharide. It also led to the discovery of novel disaccharides with improved tumor selectivity.
ContributorsMathilakathu Madathil, Manikandadas (Author) / Hecht, Sidney M. (Thesis advisor) / Rose, Seth (Committee member) / Woodbury, Neal (Committee member) / Arizona State University (Publisher)
Created2013