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1
Psalti, Ioanna S. M. "Microelectrodes : single and arrays in electron transfer." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302826.
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2
Beoku-Betts, D. F. "Electron transfer reactions of photosynthetic proteins." Thesis, University of Newcastle Upon Tyne, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353440.
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3
Langen, Ralf Warshel Arieh Gray Harry B. Richards John. "Electron transfer in proteins : theory and experiment /." Diss., Pasadena, Calif. : California Institute of Technology, 1995. http://resolver.caltech.edu/CaltechETD:etd-03062006-091606.
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4
Hart, S. E. "Electron transfer proteins in the cyanobacterium Phormidium laminosum." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603796.
Full textAbstract:
This study continues the characterisation of redox proteins of the cyanobacterium Phormidium laminosum and their interactions. So far, research has focussed on the interaction between P. laminosum Cyt f and Pc. In order to create a more complete picture of the interactions taking place in P. laminosum, this study has begun the characterisation of P. laminosum COX and four luminal subunits of P. laminosum PSI. A long-term aim of this work is to be able to compare how Pc/Cyt c6 interact with Cyt f, PSI and COX in P. laminosum. The genes of the COX complex and the luminal subunits of PSI have been cloned and their sequences analysed at the nucleotide and amino acid level. It was possible to identify residues likely to be involved in the function of the proteins. P. laminosum was also found to contain the genes for an alternative respiratory terminal oxidase (ARTO), the genes of which have been cloned. In addition, the gene for Cyt cm, which may interact with COX, has been cloned. Attempts have been made to develop expression systems for truncated versions of subunit II of COX (CtaC) and ARTO (CtaCII). Expression of an untagged- and a tagged-version of CtaC in the cytosol of E. coli have been demonstrated. In addition, comparative models for regions of CtaC and Cyt cM have been generated. From these, it has been possible to identify potential docking sites and charge-clusters, which could play a role in the interactions of both proteins. This study expands the understanding of the interaction between Cyt f and Pc of P. laminosum, by determining the role of charged residues of Cyt f in its interaction with Pc.
5
Khan, Anuja. "Solution structure and interactions of electron transfer proteins." Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415724.
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6
Kyritsis, Panayotis. "Electron-transfer reactivity of some Cu-containing proteins." Thesis, University of Newcastle Upon Tyne, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336272.
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7
Balabin, Ilya A. "Structural and dynamical control of the reaction rate in protein electron transfer /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9938586.
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8
López, Martínez Montserrat. "Electrochemical tunneling microscopy and spectroscopy of electron transfer proteins." Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/462883.
Full textAbstract:
Electron Transfer (ET) plays essential roles in crucial biological processes such as cell respiration and photosynthesis. It takes place between redox proteins and in protein complexes that display an outstanding efficiency and environmental adaptability. Although the fundamental aspects of ET processes are well understood, more experimental methods are needed to determine electronic pathways. Understanding how ET works is important not only for fundamental reasons, but also for the potential technological applications of these redox‐active nanoscale systems.
The general objective of this thesis is to investigate electron transfer in redox proteins at the single molecule level. To that end, we use Electrochemical Scanning Tunneling Microscopy (ECSTM) and conductive Atomic Force Microscopy (cAFM), excellent tools to study electronic materials and redox molecules including proteins. In this thesis, we focused on two redox protein systems: azurin, a small electron carrier protein and photosystem I, a light‐sensitive oxidoreductase protein complex.
In azurin, we studied the protein conductance as a function of its redox state and location on the protein surface, and the effect of technical parameters such as the contact properties between azurin and the metal electrodes, and the mechanical force applied in such contact. For that we adapted our ECSTM setup for an alternating current method often used in ultrahigh vacuum (UHV) STMs. We also worked in the development of a methodology that combines AFM‐based single‐molecule force measurements with single‐molecule electrical measurements, while working in an electrochemically controlled environment. These techniques can lead to a more detailed description of the ET pathways, and to a deeper understanding of the complex relation between the structure of redox proteins and their electronic properties.
In photosystem I, developed a method to immobilize complexes on a substrate suitable for ECSTM imaging and spectroscopy, atomically flat gold. In these conditions, we characterized photosystem I by imaging and spectroscopy, and evaluated its conductance and distance‐decay properties in a wide range of biologically relevant electrochemical potentials.
The characterization of conduction pathways in redox proteins at the nanoscale would enable important advances in biochemistry and would cause a high impact in the field of nanotechnology.La transferencia de electrones (ET) desempeña papeles esenciales en procesos biológicos cruciales como la respiración celular y la fotosíntesis. Tiene lugar inter‐ e intra‐ proteínas redox y en complejos de proteínas que muestran una eficiencia excepcional y gran capacidad de adaptación ambiental. Aunque los aspectos fundamentales de los procesos de ET se han estudiado en profundidad, se necesitan más métodos experimentales para determinar las vías electrónicas de ET. La comprensión de cómo funciona la ET es importante no sólo por razones fundamentales, sino también por las potenciales aplicaciones tecnológicas de estos sistemas redox nanoscópicos. El objetivo general de esta tesis es investigar la transferencia de electrones en las proteínas redox a nivel de molécula individual. Para ello utilizamos la Microscopía de Túnel Electroquímico (ECSTM) y la Microscopía de Fuerza Atómica Conductor (cAFM), que son excelentes herramientas para estudiar materiales electrónicos y moléculas redox, incluyendo proteínas. En esta tesis, nos centramos en dos sistemas de proteínas redox: azurina, una pequeña proteína portadora de electrones y el fotosistema I, un complejo de proteína oxidorreductasa sensible a la luz. En el estudio de la azurina, estudiamos la conductancia de las proteínas en función de su estado redox y el efecto de parámetros técnicos como las propiedades de contacto entre la azurina y los electrodos metálicos, y la fuerza mecánica aplicada en dicho contacto. Para ello hemos adaptado nuestra configuración de ECSTM para un método de corriente alterna a menudo utilizado en Microscopía de Túnel de ultra alto vacío (UHV‐STM). También trabajamos en el desarrollo de una metodología que combina medidas de fuerza de una sola molécula basadas en AFM con medidas eléctricas, mientras trabajamos en un ambiente controlado electroquímicamente. Estas técnicas pueden conducir a una comprensión más profunda de las vías de ET y de la compleja relación entre la estructura de las proteínas redox y sus propiedades electrónicas. En el estudio del fotosistema I, desarrollamos un método para inmovilizar complejos sobre un sustrato adecuado para la obtención de imágenes y espectroscopía con ECSTM, oro atómicamente plano. En estas condiciones, caracterizamos el fotosistema I mediante imágenes y espectroscopia, y evaluamos sus propiedades de conductancia y sus parámetros de decaimiento de la corriente con la distancia, en una amplia gama de potenciales electroquímicos biológicamente relevantes. La caracterización de las vías de conducción en las proteínas redox a escala nanométrica puede permitir importantes avances en bioquímica y causar un alto impacto en el campo de la nanotecnología.
9
Hartshorn, R. T. "Kinetic studies of some Fe containing electron-transfer proteins." Thesis, University of Newcastle Upon Tyne, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383993.
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10
Yanagisawa, Sachiko. "Active Site Engineering of Copper-Containing Electron Transfer Proteins." Thesis, University of Newcastle upon Tyne, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.484818.
Full textAbstract:
Cupredoxins arc electron transfer (ET) proteins which possess type I (Tl) copper sites. A TI copper ion is equatorially coordinated by the thiolate sulfur of a Cys and the imidazole nitrogens of two His residues, along with usually an axially coordinating thioether sulfur of a Met [azurin (Az) possess a second axial interaction with a backbone carbonyl oxygen]. Thr~e of these ligands (Cys, a His and Met) are found on a C-terminal loop which links two of the strands of the cupredoxin p-barrel scaffold. The length and sequence of this Tl copper-binding loop varies. The shOltest known Tl binding loop (that of amicyanin, Ami) has been introduced into three different cupredoxin scaffolds. All of the . loopcontraction variants possess copper centres with authentic TI properties and are redox active. The Cu(lI) and Co(II) sites experience only small structural alterations upon loop contraction with the largest changes in the Az variant (AzAmi) which can be ascribed to the removal of a hydrogen bond to the coordinating thiolate sulfur of the Cys ligand. In all cases loop-contraction leads to an increase in the pKa of the His ligand found on the loop in the reduced proteins, and in the pseudoazurin (Paz) and plastocyanin (Pc) variants the values are almost identical to that of Ami (~6.7). Thus in Paz, Pc and Ami the length of this loop tunes the pKa of the His ligand. In the AzAmi variant the pKa is 5.5 which is considerably higher than the estimated value for Az « 2) and other controlling factors, along with loop length, are involved. The reduction potentials (EmS) of the loop-contraction variants are all lower than those of the wild type (WT) proteins by ~ 30-60 mV and thus this property of a Tl copper site is finetuned by the C-tenninalloop. The electron self-exchange (ESE) rate constant (kESE) of Paz is diminished significantly by the introduction of a shorter loop. However, in PcAmi only a 2-fold decrease is observed and in AzAmi there is no effect, and thus in these two cupredoxins loop contraction does not signi~cantly influence ET reactivity. Loop-contraction provides an active site environment in all of the cup.re~oxins which is preferable for Cu(ll), whereas previous loop elongation experiments always favoure..d the cuprous site. Thus the ligand-containing loop plays an important role in tuning the entatic nature ora TI copper centre. The thiolate sulfur of the Cys ligand in Az is hydrogen bonded from the backbone amides of .Asn47 and Phe114. One of these interactions has been removed in the Phel14Pro variant. A unique . I'~ pectr~s~opj~=..featur~ ,of A.z is-the position of.the S(Cys)~Cu(Il),.ligand-to-metalcharge-transfer . - .. .' ~, . . .' . . (LMCT) band in its UVNis spectrum (~ 630 nm) which is shifted to 599 nm in the Phel14Pro variant, although a site with classic Tl properties is maintained. Shorter CU(Il)-SO(Metl21) and longer Cu(lI}O( Gly45) distances are found at the active site in the crystal structure of the variant compared to WT Az. The copper centre of Phel14Pro Az is more like those of Pc, Ami and Paz than the trigonal bipyramidal arrangement found in Az. The Phel14Pro mutation results in an 80 mV decrease in Em and an order of magnitude smaller kESE value. The influence of this mutation on Em is due to a number of structural effects ofthe mutation, with removal of the hydrogen bond probably most significant. Comparison of the active site structures of Cu(ll) and Cu(I) Phe114Pro· Az indicate larger changes upon redox interconversion than those in the WT protein which increases the reorganization energy and results in slower ET. The axial ligand at Tl copper sites is not conserved. In most cases a weakly coordinated thioether sulfur from a Met [Cu(II)-S5 ~ 2.6-3.3 A] is found in the axial position as in Pc, Paz, Az and Ami. A strong axial bond [Cu(II)-Otl of ~ 2.2 A] is sometimes provided by a Gln.[as in the stellacyanins (STCs)] and the axial ligand can be absent (a Val, Leu or Phe in the axial position) as in ceruloplasmin, FeOp, fungal laccases and some plantacyanins (PLTs). Cucumber basic protein (CBP) is a PLT which has a relatively short Cu(II)-S5(Met89) axial bond (2.6 A). The Met89Gln variant of CBP has a kE?E' a measure of intrinsic ET reactivity, ~ 7 times lower than that of the WT protein. The Met89Vai mutation to CBP results in a 2-fold increase in kESE' As the axial interaction decreases from strong Oel of Gin to relatively w.eak S5 of Met to no ligand (Val), ESE reactivity is enhanced by - 1 order of magnitude whilst Em increases by - 350 mY. The variable coordination position at this ubiquitous ET site provides a mechanism for tuning the driving force to optimize ET with the correct partner without significantly compromising intrinsic reactivity. The enhanced reactivity of a three-coordinate Tl copper site will facilitate intramolecular ET in fungallaccases and Fet3p. The phytocyanins form a sub-family of the cupredoxins and are made up of the STCs, PLTs and uc1acyanins. All of the phytocyanins exhibit an alkaline transition which results in the S(Cys)~Cu(II) LMCT band shifting - 20 nm to higher energy at elevated pH (pKa - 10). The alkaline transition influences all of the coordinating residues with the Cys ligand most affected. The exact cause of alkaline transition is not known, although deprotonation of a group close to the active site must be involved, and the side chain of the axial Gin ligand has been suggested as the trigger for this effect in the STCs. The influe!lce of pH on the spectrosco~ic properties of WT CBP and the Met89Gln and Met89Vai axial ligand variants has been studied. The alkaline transition has a similar influence on . the visible spectrum in all three proteins although the pKa value in Met89Vai CBP is smaller (8.9) than for the other two proteins (- 9.7). Thus the axial ligand is not the cause ofthe alkaline transition. The surface exposed Met16 residue of Paz is situated close to the His81 ligand in the centre of the protein's hydrophobic patch. To study the importance of Met'i6, and to attempt to introduce a 1t-1t. interaction with the imidazole ring of His81, the Met16Phe and Met16Trp variants have been prepared and characterized. NMR studies indicate that the introduced aromatic groups are oriented parallel to the imidazole ring of His8l. UVNis, EPR and paramagnetic IH NMR spectra of the Cu(II) variants highlight very similar active site structures in the two mutants which are less tetragonally distorted than in the WT protein. The pKa value for the His81 ligand in the Cu(I) proteins decreases from 4.9 in WT Paz to 4.5 and 4.1 in Metl6Phe and Metl6Trp Paz respectively, indicating that 1t-1t contact with the introduced aromatic ring stabilizes the Cu-N51 (His81) interaction. The enhanced rigidity at the active site may contribute to decr~ased reorganization energies in the variants resulting in - 2-fold and - 3-fold larger kESE values in Met16Phe alid Metl6Trp Paz respectively. These mutations could also contribute to tl~e increased kESE values by facilitating homo-dimer formation: The Metl6Phe and Metl6Trp mutations give rise to approximately 40-60 mV increases in the Em of Paz. The physiological function of Paz is donation of electrons to nitrite reductace (NiR) and the influence of these mutations on Em result in a decreased driving force for this ET reaction and smaller kC31 are found. The Km for the reaction with NiR is - 2-fold larger for the Met16Phe variant whilst similar values are found for Met 16Trp Paz and the WT protein. Introduction of a 1t-1t interaction at the active site of Paz leads to subtle structural changes but has little effect on the interaction with the physiological ET partner.
11
Cook, Shaun. "Electron transfer rates at a metal, a semiconductor and a semimetal." Thesis, University of Newcastle upon Tyne, 2013. http://hdl.handle.net/10443/2082.
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Electrochemical kinetic measurements were made on viologens in acetonitrile and ferrocene moieties bound to n-type silicon. A collection of hitherto unreported rate constants were obtained, and novel approaches to analysing electrochemical data proposed and demonstrated. Full abstract available online.
12
Bhattacharyya, Anjan Kumar. "Intramolecular and intracomplex electron transfer in water soluble redox proteins." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184339.
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Electron transfer to and between the redox centers of milk xanthine oxidase was investigated by laser flash-photolysis. Evidence is presented for slow equilibration of electrons (k < 38 s⁻¹) between the various redox centers of the enzyme. The enzyme-bound flavin and the heme moieties of the flavoprotein and cytochrome subunits of p-cresol methyl hydroxylase from Pseudomonas putida are both reduced rapidly in a second order manner by 5-dRF generated by the laser flash, followed by slower first order intramolecular electron transfer (k = 220 s⁻¹) from the protein-bound neutral flavin radical to the oxidized cytochrome. Complex formation between spinach ferredoxin:NADP⁺-reductase (FNRₒᵪ), spinach ferredoxin (Fdₒᵪ), rubredoxin (Rdₒᵪ) from Clostridium pasteurianum, two homologous HIPIP's from Ectothiorhodospira halophila (iso-1 and iso-2) and two homologous cytochromes (cytochromes-c₂ from Paracoccus denitrificans and Rhodospirrilum rubrum) have been investigated. Evidence is presented supporting the formation of 1:1 complexes that are stabilized by attractive electrostatic interactions at low ionic strength. Kinetic studies of the above-mentioned complexes provide evidence for extremely rapid to relatively slower intracomplex electron transfer rates (k 7000 s⁻¹ to 4 s⁻¹). In addition the effect of complexation on the degree of accessibility of the various redox centers of the respective complexes to reduction by small reductants such as 5-dRF· and LfH· generated by the laser flash has been evaluated. The effect of both pH and ionic strength on the second order rate of reduction and the intracomplex rates in the respective complexes have also been investigated. The results have been interpreted in terms of redox potential differences, electrostatic and structural features that influence the electron transfer rates in these systems.
13
Burch, Anita M. "Electrostatic interactions and the function of electron transfer haem proteins." Thesis, University of East Anglia, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302998.
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14
Flöck, Dagmar. "Protein-protein docking and Brownian dynamics simulation of electron transfer proteins." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=969418736.
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15
Sinclair-Day, J. D. "Kinetic studies on some Cu and Fe containing electron-transfer proteins." Thesis, University of Newcastle Upon Tyne, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356163.
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16
Bushell, K. Mark W. "Investigation into electron transfer to the periplasm for c-type cytochrome biogenesis." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275599.
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17
Pershad, Harsh R. "Studies of redox proteins and enzymes using protein-film voltammetry." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325777.
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18
Saxena, Chaitanya. "Ultrafast dynamics of energy and electron transfer in DNA-photolyase." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1171317950.
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19
Wallrapp, Frank. "Mixed quantum and classical simulation techniques for mapping electron transfer in proteins." Doctoral thesis, Universitat Pompeu Fabra, 2011. http://hdl.handle.net/10803/22685.
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El
objetivo
de
esta
tesis
se
centra
en
el
estudio
de
la
transferencia
de
electrones
(ET),
una
de
las
reacciones
más
simples
y
cruciales
en
bioquímica.
Para
dichos
procesos,
obtener
información
directa
de
los
factores
que
lo
promueves,
asi
como
del
camino
de
transferencia
electronica,
no
es
una
tarea
trivial.
Dicha
información
a
un
nivel
de
conocimiento
detallado
atómico
y
electrónico,
sin
embargo,
es
muy
valiosa
en
términos
de
una
mejor
comprensión
del
ciclo
enzimático,
que
podría
conducir,
por
ejemplo,
a
un
diseño
más
eficaz
de
inhibidores.
El
objetivo
principal
de
esta
tesis
es
el
desarrollo
de
una
metodología
para
el
estudio
cuantitativo
de
la
ET
en
los
sistemas
biológicos.
En
este
sentido,
hemos
desarrollado
un
nuevo
método
para
obtener
el
camino
de
transferencia
electrónico,
llamado
QM/MM
e-‐
Pathway,
que
se
puede
aplicar
en
sistemas
complejos
con
ET
de
largo
alcance.
El
método
se
basa
en
una
búsqueda
sucesiva
de
residuos
importantes
para
la
ET,
utilizando
la
modificación
de
la
región
quantica
en
métodos
mixtos
QM/MM,
y
siguiendo
la
evolución
de
la
densidad
de
espín
dentro
de
la
zona
de
transferencia.
Hemos
demostrado
la
utilidad
y
la
aplicabilidad
del
algoritmo
en
el
complejo
P450cam/Pdx,
identificando
el
papel
clave
de
la
Arg112
(en
P450cam)
y
del
Asp48
(en
Pdx),
ambos
conocidos
en
la
literatura.
Además
de
obtener
caminos
de
ET,
hemos
cuantificado
su
importancia
en
términos
del
acoplamiento
electrónico
entre
el
dador
y
aceptor
para
los
diferentes
caminos.
En
este
sentido,
se
realizaron
dos
estudios
de
la
influencia
del
solvente
y
de
la
temperatura
en
el
acoplamiento
electrónico
para
sistemas
modelo
oligopéptidos.
Ambos
estudios
revelaron
que
los
valores
del
acoplamiento
electrónico
fluctúan
fuertemente
a
lo
largo
de
las
trayectorias
de
dinámica
molecular
obtenidas,
y
el
mecanismo
de
transferencia
de
electrones
se
ve
ampliamente
afectado
por
el
espacio
conformacional
del
sistema.
La
combinación
del
QM/MM
e-‐pathway
y
de
los
cálculos
de
acoplamiento
electronico
fueron
utilizados
finalmente
para
investigar
la
ET
en
el
complejo
CCP/Cytc.
Nuestros
hallazgos
indican
el
papel
fundamental
del
Trp191
en
localizar
un
estadio
intermedio
para
la
transferencia
electronica,
así
como
el
camino
ET
principal
que
incluye
Ala194,
Ala193,
Gly192
y
Trp191.
Ambos
hallazgos
fueron
confirmados
a
través
de
la
literatura.
Los
resultados
obtenidos
para
el
muestro
de
manios
de
ET,
junto
con
su
evaluación
a
través
de
cálculos
de
acoplamiento
electrónico,
sugieren
un
enfoque
sencillo
y
prometedor
para
investigar
ET
de
largo
alcance
en
proteínas.The focus of this PhD thesis lies on electron transfer (ET) processes, belonging to the simplest but most crucial reactions in biochemistry. Getting direct information of the forces driving the process and the actual electron pathway is not a trivial task. Such atomic and electronic detailed information, however, is very valuable in terms of a better understanding of the enzymatic cycle, which might lead, for example, to more efficient protein inhibitor design. The main objective of this thesis was the development of a methodology for the quantitative study of ET in biological systems. In this regard, we developed a novel approach to map long-‐range electron transfer pathways, called QM/MM e-‐Pathway. The method is based on a successive search for important ET residues in terms of modifying the QM region following the evolution of the spin density of the electron (hole) within a given transfer region. We proved the usefulness and applicability of the algorithm on the P450cam/Pdx complex, indicating the key role of Arg112 of P450cam and Asp48 of Pdx for its ET pathway, both being known to be important from the literature. Besides only identifying the ET pathways, we further quantified their importance in terms of electronic coupling of donor and acceptor incorporating the particular pathway residues. Within this regard, we performed two systematic evaluations of the underlying reasons for the influence of solvent and temperature onto electronic coupling in oligopeptide model systems. Both studies revealed that electronic coupling values strongly fluctuate throughout the molecular dynamics trajectories obtained, and the mechanism of electron transfer is affected by the conformational space the system is able to occupy. Combining both ET mapping and electronic coupling calculations, we finally investigated the electron transfer in the CcP/Cytc complex. Our findings indicate the key role of Trp191 being the bridge-‐localized state of the ET as well as the main pathway consisting of Ala194, Ala193, Gly192 and Trp191 between CcP and Cytc. Both findings were confirmed through the literature. Moreover, our calculations on several snapshots state a nongated ET mechanism in this protein complex. The methodology developed along this thesis, mapping ET pathways together with their evaluation through electronic coupling calculations, suggests a straightforward and promising approach to investigate long-‐range ET in proteins.
20
Riehm, Jan Leo [Verfasser], and Michael [Akademischer Betreuer] Hutter. "Molecular simulations on electron transfer proteins / Jan Leo Riehm ; Betreuer: Michael Hutter." Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2018. http://d-nb.info/1169132537/34.
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21
Westlake, Andrew C. G. "Studies on the cytochrome P450â†câ†aâ†m enzyme system." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365833.
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22
Lowe, V. J. "The modification of electrode surfaces." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379931.
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23
Chan, Hak Tak Claude. "The 'methanol oxidase' system in an acidophilic methylotroph, Acetobacter methanolicus." Thesis, University of Southampton, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303021.
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24
Tsybin, Youri. "High Rate Electron Capture Dissociation Fourier Transform Ion Cyclotron Resonance Mass Spectrometry." Doctoral thesis, Uppsala universitet, Jonfysik, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4136.
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Advances in science and technology during the past decade have greatly enhanced the level of the structural investigation of macromolecules – peptides and proteins. Biological mass spectrometry has become one of the most precise and sensitive techniques in peptide and protein analysis. However, increasing demands of biotechnological applications require further progress to be made. In the present thesis the development and improvement of peptide and protein characterization methods and techniques based on ion-electron and ion-photon reactions in electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry are described. The focus is on the development of the electron capture dissociation method, recently discovered by the group of professor McLafferty, into a high rate, efficient tandem mass spectrometrical technique. The rate and reliability of the electron capture dissociation technique were greatly increased by implementation of low-energy pencil electron beam injection systems based on indirectly heated dispenser cathodes. Further implementation of a hollow electron beam injection system combined, in a single experimental configuration, two rapid fragmentation techniques, high rate electron capture dissociation and infrared multiphoton dissociation. Simultaneous and consecutive irradiations of trapped ions with electrons and photons extended the possibilities for ion activation/dissociation reaction schemes and lead to improved peptide and protein characterization. Using these improvements, high rate electron capture dissociation was employed in time-limited experiments, such as liquid chromatography–tandem mass spectrometry and capillary electrophoresis-tandem mass spectrometry. The analytical applications of the developed techniques have been demonstrated in top-down sequencing of peptides and proteins up to 29 kDa, improved sequencing of peptides with multiple disulfide bridges and secondary fragmentation (w-ion formation), as well as extended characterization of peptide mixtures separated by liquid chromatography and capillary electrophoresis. For instance, the dissociation of peptides resulting from enzymatic digestion of proteins provided complementary structural information on peptides and proteins, as well as their post-translational modifications.
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Bewley, Kathryn Duffy. "Characterization of electron-transfer proteins: archaeal disulfide bonds and bacterial multi-heme cytochromes c." Thesis, Boston University, 2013. https://hdl.handle.net/2144/12715.
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Thesis (Ph.D.)--Boston University
PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.Electron-transfer proteins that are responsible for redox homeostasis and long. range electron transfer are vital to intracellular and extracellular processes. In this thesis, several examples of electron-transfer proteins are studied in order to determine the emergent properties of multi-electron transfer chemistry. Thioredoxin (Trx) is a small redox-active protein that functions via its disulfide bond. These disulfides, characterized by a CXXC motif, are found to have a range of redox potentials that are often linked to function. Chapter 2 uses a set of archaeal thioredoxins from Thermoplasma acidophilum and Archaeoglobus fulgidus to test the current hypotheses using protein film voltammetry and solution-based experiments that examine folding energies. Thioredoxin reductase (TrxR) functions to provide reducing equivalents to Trx to keep it active in the cell. The TrxR from Thermoplasma acidophilum has been noted to be unusual in that it does not use NADPH as a reductant, as found in most TrxRs. The reaction between T. acidophilum Trx and TrxR is explored in Chapter 3 and a bioinfonnatic analysis of TaTrxR is included in Chapter 4 to better understand its relationship in the TrxR protein family, as well as attempt to identity its native reductant. In Chapter 5, the periplasmic decaheme cytochrome DmsE from Shewanella oneidensis is biochemically characterized. This protein is part of the dimethyl sulfoxide reduction pathway and is compared with MtrA, the well-studied decaheme protein from the dissimilatory metal reduction pathway in Shewanella. Additionally, a Cytoscape analysis of the MtrA/DmsE and OmcA protein families is presented. Finally, Chapter 6 explores the electrochemical properties of two multi-heme proteins from Nitrosomonas europaea: cytochrome c554 and hydroxylamine oxidoreductase (HAO). Cytochrome c554, a tetraheme cytochrome, has been shown to have cooperativity between two of its heme groups and gating has been. observed in protein film voltammetry (PFV) experiments. This gating is further explored in this Chapter. The enzymatic hydroxylamine reduction by HAO, a reverse reaction, is also presented.
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Pearson, Douglas C. "Brownian dynamics study of the interaction between Cytochrome F and Mobile Electron Transfer Proteins /." The Ohio State University, 1999. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488193272066355.
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Sarma, Ranjana. "Investigations of nucleotide-dependent electron transfer and substrate binding in nitrogen fixation and chlorophyll biosynthesis." Thesis, Montana State University, 2009. http://etd.lib.montana.edu/etd/2009/sarma/SarmaR1209.pdf.
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The studies presented in this thesis include studies of nucleotide-dependent conformations of the electron donor protein in nitrogenase and dark-operative protochlorophyllide reductase (DPOR) characterized using small-angle x-ray scattering and x-ray diffraction methods. Nitrogen fixation and chlorophyll synthesis are involved in the reduction of high energy bonds under physiological conditions. Both make use of elegant reaction mechanisms made possible by complex enzyme systems which are evolutionarily related. Nitrogenase reduces nitrogen to ammonia and is a two-component metalloenzyme composed of Fe protein and MoFe protein. For nitrogen reduction, the Fe protein and MoFe protein associate and dissociate in a manner concomitant with hydrolysis of at least two MgATP molecules and enables the concomitant transfer of at least one electron from Fe protein to MoFe protein. During chlorophyll biosysnthesis, the rate limiting step is catalyzed by a two-component metalloenzyme called DPOR. The two components of DPOR are BchL and BchNB proteins and these share high level of sequence similarity with the Fe protein and the MoFe protein, respectively. Based on this sequence similarity and biochemical data available, it is proposed that the reaction mechanism is similar to nitrogenase mechanism in which the components of DPOR associate and dissociate in a nucleotide dependent manner, to enable intercomponent electron transfer. Fe protein and BchL present as unique examples of proteins that couple nucleotide dependent conformational change to enable electron transfer for high energy bond reduction. The present studies have been directed at studying the low resolution studies of MgATP-bound wild-type Fe protein and its comparison to the structure of the proposed mimic, i.e, L127 Delta Fe protein. The studies presented show evidence of the MgATP-bound wild-type Fe protein having a conformation very different from the L127 Delta Fe protein. The chapters also include detailed characterization of the structure of BchL in both MgADP bound and nucleotide-free states which offer detailed insights in the structure based mechanism of BchL, with primary focus on identifying key residues involved in componenet docking and in electron transfer. Together, the studies on the Fe protein and BchL have furthered our understanding of mechanism of electron transfer in these complex enzyme systems.
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Gonzalez, Aravena Arely Carolina. "Strategies to enhance extracellular electron transfer rates in wild-type cyanobacterium Synechococcus elongatus PCC7942 for photo-bioelectricity generation." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274353.
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The aim of this thesis is to enhance the extracellular electron transfer rates (exoelectrogenesis) in cyanobacteria, to be utilised for photo-bioelectricity generation in biophotovoltaics (electrochemical cell). An initial cross comparison of the cyanobacterium Synechococcus elongatus PCC7942 against other exoelectrogenic cultures showed a hindered exoelectrogenic capacity. Nonetheless, in mediatorless biophotovoltaics, it outperformed the microalgae Chlorella vulgaris. Furthermore, the performance of S. elongatus PCC7942 was improved by constructing a more efficient design (lower internal resistance), which was fabricated with carbon fibres and nitrocellulose membrane, both inexpensive materials. To strategically obtain higher exoelectrogenic rates, S. elongatus PCC7942 was conditioned by iron limitation and CO2 enrichment. Both strategies are novel in improving cyanobacteria exoelectrogenesis. Iron limitation induced unprecedented rates of extracellular ferricyanide reduction (24-fold), with the reaction occurring favourably around neutral pH, different to the cultural alkaline pH. Iron limited cultures grown in 5% and 20% CO2 showed increased exoelectrogenic rates in an earlier stage of growth in comparison to air grown cultures. Conveniently, the cultural pH under enriched CO2 was around neutral pH. Enhanced photo-bioelectricity generation in ferricyanide mediated biophotovoltaics was demonstrated. Power generation was six times higher with iron limited cultures at neutral pH than with iron sufficient cultures at alkaline pH. The enhanced performance was also observed in mediatorless biophotovoltaics, especially in the dark phase. Exoelectrogenesis was mainly driven by photosynthetic activity. However, rates in the dark were also improved and in the long term it appeared that the exoelectrogenic activity under illumination tended to that seen in the dark. Proteins participating in iron uptake by an alleged reductive mechanism were overexpressed (2-fold). However, oxidoreductases in the outer membrane remain to be identified. Furthermore, electroactive regions in biofilms of S. elongatus PCC7942 were established using cyclic voltammetry. Double step potential chronoamperometry was also successfully tested in the biofilms. Thus, the electrochemical characterisation of S. elongatus PCC7942 was demonstrated, implying that the strategies presented in this thesis could be used to screen for cyanobacteria and/or electrode materials to further develop systems for photo-bioelectricity generation.
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Kessinger, Matthew Carl. "The Influence of Inner-Sphere Reorganization on Rates of Interfacial Electron Transfer in Transition Metal-Based Redox Electrolytes." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/100128.
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Photovoltaic (PV) technologies are a promising approach to achieve clean, renewable energy production on a global scale. However, the widespread implementation of this technology is limited due to the intricate challenges associated with its complex electrochemical processes. One such challenge is the formation of long-lived charge-separated states (CSSs), a process that directly influences device efficiencies. Viable strategies for increasing CSS lifetimes involve the inhibition of parasitic back-electron transfer pathways. In liquid-junction PVs, electronic recombination is prevented by utilizing redox electrolytes that promote directional electron transfer at the electrode/electrolyte interface, where forward electron transfer (i.e. to the electrode) is favored and the corresponding electronic recombination reaction is impeded. To meet this criterion, researchers seek to employ redox electrolytes that undergo a spin-exchange reaction induced by electron transfer. This event, known as charge transfer-induced spin crossover (CTISC), significantly increases the reorganization energy associated with electronic recombination, producing long-lived CSSs and elevated device efficiency.
This dissertation describes a suite of manganese-based redox mediators that exhibit CTISC across a tunable range (1.5 V) of formal potentials (E1/2). These complexes are utilized as redox electrolytes in liquid-junction PVs and result in a two-fold enhancement in the device efficiency relative to other CTISC redox species. Photosensitizer regeneration rates are monitored using transient absorption spectroscopy (TAS) to discern the optimal E1/2 values in this class of complexes while density functional theory is employed to calculate the reorganization energy of each species. By implementing these promising electrolytes into PV devices, scientists and engineers are armed with new tools to increase the accessibility and efficiency of next-generation PVs, thereby transforming past promises into progress.Doctor of Philosophy
To realize next-generation renewable fuels, scientists must understand how electron transfer at an interface is controlled. This dissertation highlights one method of forming a chemically useful and long-lived charge separated state. The formation of this charge separated state is achieved through an electronic reorganization that occurs at a metal center after electron transfer. Chapters 2, 3, and 4 investigate the synthesis and characterization of new metal species that possess this electronic reorganization process and provide an advanced understanding of how this process facilitates the formation of long-lived charge separated states. This work is intended to motivate new schools of thought that aid the design of next-generation catalytic materials for light-driven chemical reactions.
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Medvedev, Dmitry. "Computation of electron transfer in proteins : method development and applications to cytochrome c oxidase and DNA photolyase /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2002. http://uclibs.org/PID/11984.
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Carter, Chet. "Modification of Indium-Tin Oxide Surfaces: Enhancement of Solution Electron Transfer Rates and Efficiencies of Organic Thin-Layer Devices." Diss., The University of Arizona, 2006. http://hdl.handle.net/10150/195405.
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This dissertation has focused on the study of the ITO/organic heterojunction and the chemistries therein, it proposes appropriate strategies that enhance the interfacial physical and electronic properties for charge injection with application to organic thin-layer devices. We focused on four major aspects of this work: i) To characterize the ITO surface and chemistries that may be pertinent to interaction with adjacent organic layers in a device configuration. This developed a working model of surface and provided a foundation for modification strategies. Characterization of the electronic properties of the surface indicate less than 5% of the geometrical surface is responsible for the bulk of current flow while the rest is electrically inactive. ii) To determine the extent to which these chemistries are variable and propose circumstances where compositional changes can occur. It is shown that the surface chemistry of ITO is heterogeneous and possible very dynamic with respect to the surrounding environment. iii) To propose a strategy for modification of the interface. Modification of ITO surfaces by small molecules containing carboxylic acid functionalities is investigated. Enhancements in the electron transfer rate coefficient were realized after modification of the ITO electrode. The enhancements are found to stem from a light etching mechanism. Additionally, an elecro-catalytic effect was observed with some of the modifiers. iv) Apply these modifications to organic light emitting diodes (OLEDs) and organic photovoltaic devices (OPVs). Enhancements seen in solution electrochemical experiments are indicative of the enhancements seen for solid state devices. Modifications resulted in substantially lower leakage currents (3 orders of magnitude in some cases) as well as nearly doubling the efficiency.An additional chapter describes the creation and characterization of electrochemically grown polymer nano-structures based on blazed angle diffraction gratings. The discussion details the micro-contact printing process and the electro-catalytic growth of the conductive polymers PANI and PEDOT to form diffraction grating structures in their own right. The resulting diffraction efficiency of these structures is shown to be sensitive to environmental conditions outlining possible uses as chemical sensors. This is demonstrated by utilizing these structures as working pH and potentiometric sensors based on the changing diffraction efficiency.
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Thorn, Penny Anne, and penny thorn@flinders edu au. "Electronic State Excitations in the Water Molecule by Collisions with Low Energy Electrons." Flinders University. Chemistry, Physics and Earth Sciences, 2008. http://catalogue.flinders.edu.au./local/adt/public/adt-SFU20080714.112505.
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The present study was largely concerned with measuring accurate absolute values for the electronic state excitation cross sections in H2O, in the incident electron energy range 15eV to 50eV. It is hoped that these data will eventually help to improve the current state of electron - molecule scattering theory, as well as being useful in various fields of modelling. As an illustration of this latter point, the cross sections determined here were used to calculate quantities of importance in atmospheric modelling, namely, electron energy transfer rates and rates for the excitation of water molecules by auroral secondary electrons.
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Bose, Saumyaditya. "Bioreduction of Hematite Nanoparticles by Shewanella oneidensis MR-1." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/30189.
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A dissertation is presented on the bioreduction of hematite (α-Fe2O3) nanoparticles. The study shows that an alternative extracellular electron transfer mechanism other than the classical 'direct-contact' mechanism may be simultaneously employed by Shewanella oneidensis MR-1 during solid-phase metal reduction. This conclusion is supported by analysis of the bioreduction kinetics of hematite nanoparticles coupled with microscopic investigations of cell-mineral interactions. The reduction kinetics of metal-oxide nanoparticles were examined to determine how S. oneidensis utilizes these environmentally-relevant solid-phase electron acceptors. Nanoparticles involved in geochemical reactions show different properties relative to larger particles of the same phase, and their reactivity is predicted to change as a function of size. To demonstrate these size-dependent effects, the surface area normalized reduction rates of hematite nanoparticles by S. oneidensis MR-1 with lactate as the sole electron donor were measured. As evident from whole cell TEM analysis, the mode of nanoparticle adhesion to cells is different between the more aggregated, pseudo-hexagonal to irregular shaped 11 nm, 12 nm, 99 nm and the less aggregated 30 nm and 43 nm rhombohedral particles. The 11 nm, 12 nm and 99 nm particles show less cell contact and coverage than the 30 nm and 43 nm particles but still show significant rates of reduction. This leads to the provisional speculation that S. oneidensis MR-1 employs a pathway of indirect electron transfer in conjunction with the direct-contact pathway, and the relative importance of the mechanism employed depends upon aggregation level and the shape of the particles or crystal faces exposed. In accord with the proposed increase in electronic band-gap for hematite nanoparticles, the smallest particles (11 nm) exhibit one order of magnitude decrease in reduction when compared with larger (99 nm) particles, and the 12 nm rates fall in between these two. This effect may also be due to the passivation of the mineral and cell surfaces by Fe(II), or decreasing solubility due to decrease in size.Ph. D.
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Harris, Roger Lyndon. "Studies in intermolecular electron transfer between the copper-containing proteins azurin I and nitrate reductase from Alcaligenes xylosoxidans." Thesis, University of East Anglia, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399795.
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Null, Emily Mrugacz. "Temperature effects on the potential window of water and acetonitrile and heterogeneous electron transfer rates of outer sphere redox probes." Thesis, University of Iowa, 2014. https://ir.uiowa.edu/etd/1491.
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This thesis examines the effects of temperature on the electrochemistry of an aqueous solvent, HNO3, and a non aqueous solvent, acetonitrile and their respective analytes. It has been demonstrated previously that lowering the temperature of a solvent expands the available potential window in which to perform electrochemical experiments. The working window of an aqueous solvent is limited by the electrolysis of water. Cyclic voltammetry was utilized to examine the temperature effects on the rates of the oxidation and reduction of the solvent as well as the effects on the redox species in solution. The redox species experienced decreased peak splitting with lower temperatures, and the diffusion constants and rate constants were lowered as the temperature decreased. It was determined that the solvent window of the HNO3 solution was extended in experiments conducted at lower temperatures. The voltage window went from 2.349 V at 25 °C to 2.671 V at 5 °C. No significant improvement in the voltage window of acetonitrile was seen at lower temperatures. Rate constants for the oxidation and reduction of water were lowered and the voltage window of nitric acid expanded.
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Kollipara, Sireesha. "Theoretical studies of rates of electron transfer between cytochrome b₅ reductase and cytochrome b₅ a thesis presented to the faculty of the Graduate School, Tennessee Technological University /." Click to access online, 2008. http://proquest.umi.com/pqdweb?index=0&did=1674959791&SrchMode=1&sid=2&Fmt=6&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1268413954&clientId=28564.
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Cao, Yu. "I. Synthesis Of Anthraquinone Derivatives For Electron Transfer Studies In DNA. II. Characterization Of The Interaction Between Heme And Proteins." Digital Archive @ GSU, 2011. http://digitalarchive.gsu.edu/chemistry_diss/55.
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Anthraquinone (AQ) derivatives with relatively high reduction potentials have been synthesized to afford good candidates for electron transfer studies in DNA. Electron withdrawing groups on the anthraquinone ring gave derivatives with less negative reduction potentials. The anthraquinone imide (AQI) derivatives had reduction potentials less negative than AQ derivatives. The AQI ring system was subject to base-induced hydrolysis.
Water-soluble sulfonated tetraarylporphyrins have been studied in a wide variety of contexts. Herein, we report the first synthesis of a pentasulfonated porphyrin bearing an internal cyclic sulfone ring. Treatment of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS4) with fuming H2SO4 gave a structure consistent with initial sulfonation followed by dehydration to give a sulfone bridge between an ortho-position of one of the phenyl groups and a β-pyrrole position on the porphine ring (TPPS4Sc). The structure was established by ESI-MS and 1HNMR. The Soret absorption is red shifted by about 32 nm compared to that of TPPS4.
Streptococcus pyogenes obtains iron by taking up heme from the environment during infection. One of the heme uptake pathways is the Sia or Hts pathway. The initial protein in this pathway is Shr, which has two heme-binding NEAT domains, NEAT1 nearer the N-terminus, and NEAT2 nearer the C-terminus. We report biophysical characteristics of these two NEAT domains. To assess stability of this domain towards heme release, denaturation studies of the Fe(II) and Fe(III) forms were performed. For each domain, both the Fe(II) and the Fe(III) forms behave similarly in thermal denaturation and guanidinium denaturation. Overall, NEAT2 is more stable than NEAT1. Spectral signatures, sequence alignment and homology modeling for both domains suggest that one of the axial ligands is methionine. NEAT2 autoreduces as the pH increases and autooxidizes as the pH decreases. Heme uptake from the host environment is the only iron acquisition pathway in S. pyogenes; inhibition of this pathway might be an approach to infection control. Compounds that might inhibit the heme uptake pathway were selected via virtual screening.
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Archipowa, Nataliya. "Mechanistic studies on the light-dependent NADPH:Protochlorophyllide Oxidoreductase and animal cryptochromes." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/mechanistic-studies-on-the-lightdependent-nadphprotochlorophyllide-oxidoreductase-and-animal-cryptochromes(667672e1-d037-4135-b4d2-71a98331834f).html.
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Nature uses sunlight either as energy source or as information carrier. Photoreception is achieved by two groups of specialised proteins: photo-enzymes that catalyse photoreactions and photosensors that initiate physiological functions. In the present work mechanistic studies were conducted on one representative of each group by using site-directed mutagenesis as well as stationary and time-resolved spectroscopy. The photo-enzyme NADPH:Protochlorophyllide Oxidoreductase (POR) catalyses the light-dependent C17-C18 double bond reduction of protochlorophyllide, including a hydride and a proton transfer, to produce chlorophyllide, the immediate precursor of chlorophyll. POR provides a unique opportunity to study the hydride transfer mechanism in detail. Three distinct intermediates, prior to product formation, were observed that were interpreted as electron and proton-coupled electron transfer reactions from NADPH indicating a sequential hydride transfer mechanism. An active-site mutant, POR-C226S, yields distinct different intermediates compared to POR wild type but ends in the same chlorophyllide stereoisomer most likely due to an altered protochlorophyllide binding. This work provides the first direct observation of a stepwise hydride transfer mechanism in a biological system. Cryptochromes (CRY) are so far defined as flavoprotein blue-light photosensors that regulate the circadian clock throughout nature and are suggested as the candidate magnetoreceptor in animals. Animal CRY are subdivided into two classes of proteins: the light-responsive Type I (invertebrates) and the light-independent Type II (mainly vertebrates). The molecular basis of their different roles in the circadian clock is still unknown. Animal Type I CRY are suggested to undergo conformational changes - required for induction of subsequent signalling cascades - induced by the change in the FAD redox state due to light absorption. The study shows that in contrast to Type I animal Type II CRY do not bind tightly FAD as a cofactor due to the lack of structural features and therefore provide the molecular basis for their different biological roles ruling out a direct photomagnetoreceptor function. Further, detailed studies on a fruit fly (Dm)CRY reveal that it does not undergo a photocycle as FAD release and Trp decomposition were observed. Thus, it is suggested that light is a negative regulator of DmCRY stability linking the initial photochemistry to subsequent dark processes leading to signal transduction on a molecular level.
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Syed, Lateef Uddin. "Nanoelectrode and nanoparticle based biosensors for environmental and health monitoring." Diss., Kansas State University, 2012. http://hdl.handle.net/2097/13701.
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Doctor of PhilosophyDepartment of Chemistry
Jun Li
Reduction in electrode size down to nanometers dramatically enhances the detection sensitivity and temporal resolution. Here we explore nanoelectrode arrays (NEAs) and nanoparticles in building high performance biosensors. Vertically aligned carbon nanofibers (VACNFs) of diameter ~100 nm were grown on a Si substrate using plasma enhanced chemical vapor deposition. SiO[subscript]2 embedded CNF NEAs were then fabricated using techniques like chemical vapor deposition, mechanical polishing, and reactive ion etching, with CNF tips exposed at the final step. The effect of the interior structure of CNFs on electron transfer rate (ETR) was investigated by covalently attaching ferrocene molecules to the exposed end of CNFs. Anomalous differences in the ETR were observed between DC voltammetry (DCV) and AC voltammetry (ACV). The findings from this study are currently being extended to develop an electrochemical biosensor for the detection of cancerous protease (legumain). Preliminary results with standard macro glassy carbon electrodes show a significant decrease in ACV signal, which is encouraging. In another study, NEA was employed to capture and detect pathogenic bacteria using AC dielectrophoresis (DEP) and electrochemical impedance spectroscopy (EIS). A nano-DEP device was fabricated using photolithography processes to define a micro patterned exposed active region on NEA and a microfluidic channel on macro-indium tin oxide electrode. Enhanced electric field gradient at the exposed CNF tips was achieved due to the nanometer size of the electrodes, because of which each individual exposed tip can act as a potential DEP trap to capture the pathogen. Significant decrease in the absolute impedance at the NEA was also observed by EIS experiments. In a final study, we modified gold nanoparticles (GNPs) with luminol to develop chemiluminescence (CL) based blood biosensor. Modified GNPs were characterized by UV-Vis, IR spectroscopy and TEM. We have applied this CL method for the detection of highly diluted blood samples, in both intact and lysed forms, which releases Fe[superscipt]3[superscript]+ containing hemoglobin to catalyze the luminol CL. Particularly, the lysed blood sample can be detected even after 10[superscript]8 dilution (corresponding to ~0.18 cells/well). This method can be readily developed as a portable biosensing technique for rapid and ultrasensitive point-of-care applications.
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Dobrev, Plamen [Verfasser], Helmut [Akademischer Betreuer] Grubmüller, Marcus [Akademischer Betreuer] Müller, and Claudia [Akademischer Betreuer] Steinem. "Protonation patterns in reduced and oxidized form of electron transfer proteins / Plamen Dobrev. Gutachter: Helmut Grubmüller ; Marcus Müller ; Claudia Steinem. Betreuer: Helmut Grubmüller." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://d-nb.info/1042345694/34.
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Pathirathne, Thusitha. "Theoretical modeling of electron transfer rates between cytochrome c and small transition metal complexes a thesis presented to the faculty of the Graduate School, Tennessee Technological University /." Click to access online, 2009. http://proquest.umi.com/pqdweb?index=0&did=1760001881&SrchMode=1&sid=2&Fmt=6&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1268409541&clientId=28564.
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Bender, Shana Lynn. "A study of protein dynamics and cofactor interactions in Photosystem I." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26463.
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Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2009.Committee Chair: Barry, Bridette; Committee Member: Doyle, Donald; Committee Member: Kelly, Wendy; Committee Member: McCarty, Nael; Committee Member: Schimdt-Krey, Ingaborg. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Hennig, Sandra Elisabeth. "Insights into the ATP-dependent reductive activation of the Corrinoid/Iron-Sulfur Protein of Carboxydothermus hydrogenoformans." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2014. http://dx.doi.org/10.18452/16984.
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Die Verknüpfung einer exergonischen mit einer endergonischen Reaktion zur Ermöglichung der letzteren ist eine in biologischen Systemen weit verbreitete Strategie. Energetisch benachteiligte Elektronenübertragungsreaktionen im Rahmen der reduktiven Aktivierung von Nitrogenasen, Radikal-abhängigen β,α-Dehydratasen, der zu diesen verwandten Benzoyl-CoA-Reduktasen und diversen Cobalamin-abhängigen Methyltransferasen sind gekoppelt an die Hydrolyse von ATP. Der Methylgruppentransfer des reduktiven Acetyl-CoA-Weges von Carboxydothermus hydrogenoformans erfordert den Co(I)-Zustand des Corrinoid/Eisen-Schwefel Proteins (CoFeSP). Um diese superreduzierte Form nach einer oxidativen Inaktivierung zu regenerieren ist ein „Reparaturmechanismus“ erforderlich. Ein offenes Leseraster (orf7), welches möglicherweise für eine reduktive Aktivase von Corrinoid Enzymen (RACE) kodiert, wurde in dem Gencluster der am reduktiven Acetyl-CoA-Weg beteiligten Proteine entdeckt. Im Rahmen dieser Arbeit wurde dieses potenzielle RACE Protein biochemisch und strukturell charakterisiert und die ATP-abhängige reduktive Aktivierung von CoFeSP untersucht. Auf Grundlage der in dieser Arbeit gewonnenen Ergebnisse wurde ein Mechanismus für die ATP-abhängige Aktivierung entworfen. Dieser gibt Einblicke wie die durch ATP-Hydrolyse bereitgestellte Energie einen energetisch ungünstigen Elektronentransfer ermöglichen kann. Hierzu kombiniert RACo das Ausgleichen von Bindungsenergien mit Modulationen am Elektronenakzeptor. Eine vergleichbare Strategie wurde bisher in keinem anderen ATP-abhängigen Elektronenübertragungssystem wie dem von Nitrogenasen, Radikal-abhängigen β,α-Dehydratasen oder Benzoyl-CoA-Reduktasen beobachtet und könnte ein für RACE Proteine allgemein gültige Eigenschaft darstellen.The principle of coupling an exergonic to an endergonic reaction to enable the latter is a widespread strategy in biological systems. Unfavoured electron transfer reactions in the reductive activation of nitrogenases, radical-dependent β,α-dehydratases and the related benzoyl- CoA reductases, as well as different cobalamin-dependent methyltransferases are coupled to the hydrolysis of ATP. The reductive acetyl-CoA pathway of Carboxydothermus hydrogenoformans relies on the superreduced Co(I)-state of the corrinoid/iron-sulfur protein (CoFeSP) that requires a “repair mechanism” in case of incidental oxidation. An open reading frame (orf7) coding for a putative reductive activase of corrinoid enzymes (RACE) was discovered in the gene cluster of proteins involved in the reductive acetyl-CoA pathway. In this work, this putative RACE protein was biochemically and structurally characterised and the ATP-dependent reductive activation of CoFeSP was investigated. Based on the results of this study, a mechanism for the ATP-dependent reactivation of CoFeSP was deduced providing insights into how the energy provided by ATP could trigger this unfavourable electron transfer. The reductive activator of CoFeSP combines balance of binding energies and modulations of the electron acceptor to promote the uphill electron transfer to CoFeSP. A comparable strategy has not been observed in other ATP-dependent electron transfer systems like nitrogenases, radical-dependent β,α-dehydratases and benzoyl- CoA reductases and could be a universal feature of RACE proteins.
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Benevides, Norma. "Relation entre l'activité herbicide de quelques composés et leur liaison à des protéines ou à des structures membranaires isolées." Grenoble 1, 1987. http://www.theses.fr/1987GRE10143.
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Le travail presente dans ce memoire est une etude des relations pouvant exister entre l'activite de composes herbicides inhibiteurs de la division cellulaire chez les vegetaux et leur liaison a des proteines (tubuline, serum albumine bovine=sab) ou a des structures membranaires (thylakoides). Nous avons constitue une serie d'inhibiteurs connus de la division cellulaire (propyzamide, butraline, pentachlorophenol=pcp, colchicine et deux phenylcarbamates: prophame et chlorprophame=cipc). Nous avons verifie leur efficacite et compare celle-ci a l'activite de 19 pyridilcarbamates nouveaux (. . . )
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Kiser, Cynthia N. "Biological electron transfer in copper proteins." Thesis, 1998. https://thesis.library.caltech.edu/8194/1/Kiser-cn-1998.pdf.
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Nature has used a variety of protein systems to mediate electron transfer. In this thesis I examine aspects of the control of biological electron transfer by two copper proteins that act as natural electron carriers.
In the first study, I have made a mutation to one of the ligand residues in the azurin blue copper center, methionine 121 changed to a glutamic acid. Studies of intramolecular electron transfer rates from that mutated center to covalently attached ruthenium complexes indicate that the weak axial methionine ligand is important not only for tuning the reduction potential of the blue copper site but also for maintaining the low reorganization energy that is important for fast electron transfer at long distances.
In the second study, I begin to examine the reorganization energy of the purple copper center in the CuA domain of subunit II of cytochrome c oxidase. In this copper center, the unpaired electron is delocalized over the entire binuclear site. Because long-range electron transfer into and out of this center occurs over long distances with very small driving forces, the reorganization energy of the CuA center has been predicted to be extremely low. I describe a strategy for measuring this reorganization energy starting with the construction of a series of mutations introducing surface histidines. These histidines can then be labeled with a series of ruthenium compounds that differ primarily in their reduction potentials. The electron transfer rates to these ruthenium compounds can then be used to determine the reorganization energy of the CuA site.
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Langen, Ralf. "Electron transfer in proteins : theory and experiment." Thesis, 1995. https://thesis.library.caltech.edu/888/1/Langen_r_1995.pdf.
Full textAbstract:
This thesis consists of two main parts and one appendix. The first part (Chapters 2 and 3) contains mainly experimental work on electron transfer in ruthenium-modified azurin mutants. The second part describes theoretical studies on the control of reduction potentials in cytochromes and feredoxins. The appendix presents calculations on the reaction mechanism for the GTP-hydrolysis in Ras p21.
In the experimental part electron tunneling through the beta-sheet in pseudomonas aeruginosa azurin is discussed. In agreement with theoretical consideration it is found that electron tunneling through a beta-strand is quite efficient. It is argued that the efficiency is due to the highly covalent nature of the bridge. Furthermore, the effects of the weakly coordinated M121 ligand and the strongly coordinated C112 ligand on the coupling are compared in Chapters 2 and 3. It is found that indeed the C112 ligand facilitates electron transfer, although the rate enhancement in the experiments does not appear to be much more than an order of magnitude.
The theoretical section (chapters 4-6) presents microscopical calculations of electrostatic effects found to be important for the control of reduction potentials. Chapter 4 analyzes the effect of the N521 mutation in cytochrome c. The calculations suggest that the change in reduction potential is due to an electrostatic effect and dominated by the loss of the N52 dipole, which compensates for the displacement of an internally bound water molecule. In chapter 5 it is concluded that the change in reduction potential for the M80H axial ligand replacement in cytochrome c is due to the effect of the ligand bonding rather than an electrostatic effect. The enormous variations in the reduction potentials of iron-sulfur clusters in several proteins are being investigated in chapter 6. The potentials mainly appear to be controlled by the number of hydrogen bonds. However, in some cases the effect of nearby water molecules need to be considered. The calculations presented in the appendix show that a previously proposed mechanism in Ras P21 does not appear energetically feasible (reprint 1). In reprint 2 an alternative mechanism is proposed.
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St, Clair Cynthia Strong. "Electrochemical and Electron Transfer Investigations of Copper Proteins." Thesis, 1989. https://thesis.library.caltech.edu/7943/2/St.%20Clair_cs_1989.pdf.
Full textAbstract:
A study of the pH and temperature dependence of the redox potentials of azurins from five species of bacteria has been performed. The variations in the potentials with pH have been interpreted in terms of electrostatic interactions between the copper site and titrating histidine residues, including the effects of substitutions in the amino acid sequences of the proteins on the electrostatic interactions. A comparison of the observed pH dependences with predictions based on histidine pK_a values known for Pseudomonas aeruginosa (Pae), Alcaligenes denitrificans (Ade), and Alcaligenes faecalis (Afa) azurins indicates that the Pae and Ade redox potentials exhibit pH dependences in line with electrostatic arguments, while Afa azurin exhibits more complex behavior. Redox enthalpies and entropies for four of the azurins at low and high pH values have also been obtained. Based on these results in conjuction with the variable pH experiments, it appears that Bordetella bronchiseptica azurin may undergo a more substantial conformational change with pH than has been observed for other species of azurin.
The temperature dependence of the redox potential of bovine erythrocyte superoxide dismutase (SOD) has been determined at pH 7.0, with potassium ferricyanide as the mediator. The following thermodynamic parameters have been obtained (T = 25°C): E°' = 403±5 mV vs. NHE, ΔG°' = -9.31 kcal/mol, ΔH°' = -21.4 kcal/mol, ΔS°' = -40.7 eu, ΔS°'_(rc) = -25.1 eu. It is apparent from these results that ΔH°', rather than ΔS°', is the dominant factor in establishing the high redox potential of SOD. The large negative enthalpy of reduction may also reflect the factors which give SOD its high specificity toward reduction and oxidation by superoxide.
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Cordas, Cristina Maria Grade Couto da Silva. "Electrochemical Studies of Electron Transfer Proteins and Electroactive Biofilms." Doctoral thesis, 2007. http://hdl.handle.net/10362/63809.
Full textAbstract:
Bioelectrochemistry has been recognized as a very important technique to get
relevant thermodynamic and kinetic information on diverse complex biological
systems. From the determination of redox potentials of metallic centers in small
electron carrier proteins to the resolution of more complex mechanisms in highly
organised enzymes, and even whole bacteria systems, the application of dynamic
electrochemical techniques has proved to be a powerful tool that has allowed to get
deeper in the understanding of such systems.
In the present thesis electrochemical techniques were used to study diverse
biochemical systems. Different approaches have been used, namely the classic bulk
systems in which the reactive species are in solution and immobilised systems where
proteins are physically constrained at the electrode surface. Within these, also
alternative methods were used, as membrane electrodes and physical adsorption of
the biological material.
Several systems of different complexity were object of study. Simple Enzymes
Small non-hemic proteins, essentially related to electron transfer processes, with
iron-sulfur centers, as desulforedoxin and other related iron-sulfur proteins,
associated with oxidative stress protection, namely superoxide reductases, were
investigated by cyclic and square wave voltammetry; its redox potentials and pH
dependence were determined.
Complex Enzymes and Catalytic Systems
Nitrogen Cycle Enzymes
Enzymes taking part in the nitrogen cycle were studied, namely the periplasmic
nitrate reductase isolated from Desulfovibrio desulfuricans ATCC 27774 and nitric
oxide reductase purifed from Pseudomonas nautica 617. The first one, responsible the nitrate reduction to nitrite, is the only known monomeric nitrate reductase
biding an iron-sulfur center and a molybdopterin co-factor. In this work it was
possible, for the first time, to observe the individual metal centers voltammetric
features. The electrocatalytic activity was also evaluated. The second enzyme, nitric
oxide reductase, promotes the two electrons reduction of NO to N2O. In this unique
work it was possible to obtain data from a nitric oxide reductase resulting from direct
electron transfer assays, accomplished by cyclic voltammetry. The demonstration of
the catalytic activity towards the oxygen reduction was achieved and the reduction
and catalysis of NO was also observed by direct electrochemistry. The pH
dependence of the catalytic center redox process was evaluated and it was possible
to show that the immobilized enzyme retained its native properties.
Production and Consumption of Hydrogen
Hydrogenase (Hase), isolated from Desulfovibrio gigas (Dg), is a multicenter enzyme
that catalyses the interconversion between H2 and H+, and that is involved in the
dissimilatory sulphate reduction pathway. In this work, the direct electrochemistry of
the Dg Hase, in bulk solution and also immobilised by adsorption, in turnover and
non-turnover conditions was studied. For the first time the redox features of the
enzyme metallic centers in non-catalytic conditions and without the addition of any of
the known enzyme inhibitors were attained. Besides, it was possible to tune the
activation and inactivation of the enzyme by dynamic potential control.
Approach to in vivo systems
Finally, the electrochemical behaviour of biofilms formed from pure cultures of
sulphate reducing bacteria, namely Desulfovibrio desulfuricans ATCC 27774 was
studied. The response of the biofilm on the electrodes was evaluated by the ratio of
current obtained in the presence/absence of the biofilm and its stability in time. For
the first time it was possible to observe that pure culture biofilms of sulphate reducing
bacteria are electroactive.
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Dobrev, Plamen. "Protonation patterns in reduced and oxidized form of electron transfer proteins." Doctoral thesis, 2012. http://hdl.handle.net/11858/00-1735-0000-000D-F0C2-8.
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"Modification of Electron Transfer Proteins in the Chlamydomonas reinhardtii Chloroplast for Alternative Fuel Development." Doctoral diss., 2013. http://hdl.handle.net/2286/R.I.20812.
Full textAbstract:
abstract: There is a critical need for the development of clean and efficient energy sources. Hydrogen is being explored as a viable alternative to fuels in current use, many of which have limited availability and detrimental byproducts. Biological photo-production of H2 could provide a potential energy source directly manufactured from water and sunlight. As a part of the photosynthetic electron transport chain (PETC) of the green algae Chlamydomonas reinhardtii, water is split via Photosystem II (PSII) and the electrons flow through a series of electron transfer cofactors in cytochrome b6f, plastocyanin and Photosystem I (PSI). The terminal electron acceptor of PSI is ferredoxin, from which electrons may be used to reduce NADP+ for metabolic purposes. Concomitant production of a H+ gradient allows production of energy for the cell. Under certain conditions and using the endogenous hydrogenase, excess protons and electrons from ferredoxin may be converted to molecular hydrogen. In this work it is demonstrated both that certain mutations near the quinone electron transfer cofactor in PSI can speed up electron transfer through the PETC, and also that a native [FeFe]-hydrogenase can be expressed in the C. reinhardtii chloroplast. Taken together, these research findings form the foundation for the design of a PSI-hydrogenase fusion for the direct and continuous photo-production of hydrogen in vivo.Dissertation/Thesis
Ph.D. Biochemistry 2013