Electron Transport

A study of the performance of five commercial radiotherapy treatment planning systems (TPSs) for common treatment sites regarding their ability to model heterogeneities and scattered photons has been performed. The comparison was based on CT information for prostate, head and neck, breast and lung cancer cases. The TPSs were installed locally at different institutions and commissioned for clinical use based on local procedures. For the evaluation, beam qualities as identical as possible were used: low energy (6 MV) and high energy (15 or 18 MV) x-rays. All relevant anatomical structures were outlined and simple treatment plans were set up. Images, structures and plans were exported, anonymized and distributed to the participating institutions using the DICOM protocol. The plans were then re-calculated locally and exported back for evaluation. The TPSs cover dose calculation techniques from correction-based equivalent path length algorithms to modelbased algorithms. These were divided into two groups based on how changes in electron transport are accounted for ((a) not considered and (b) considered). Increasing the complexity from the relatively homogeneous pelvic region to the very inhomogeneous lung region resulted in less accurate dose distributions. Improvements in the calculated dose have been shown when models consider volume scatter and changes in electron transport, especially when the extension of the irradiated volume was limited and when low densities were present in or adjacent to the fields. A Monte Carlo calculated algorithm input data set and a benchmark set for a virtual linear accelerator have been produced which have facilitated the analysis and interpretation of the results. The more sophisticated

Multiple acyl-CoA dehydrogenase deficiency CoQ 10 deficiency Riboflavin Electron transfer flavoprotein ubiquinone oxidoreductase a b s t r a c t Multiple acyl-CoA dehydrogenase deficiency (MADD) is a metabolic disorder due to dysfunction of electron transfer flavoprotein (ETF) or ETF-ubiquinone oxidoreductase (ETF-QO). Mutations in ETFDH, encoding ETF-QO have been associated with both riboflavin-responsive and non-responsive MADD as well as a myopathic form of CoQ 10 deficiency, although pathomechanisms responsible for these different phenotypes are not well-defined. We performed mutation analysis in four Taiwanese MADD patients. Three novel ETFDH mutations were identified in four patients and all harbored the p.A84T mutation. Muscle CoQ 10 levels and respiratory chain activities measured in two patients were normal. Three patients improved on riboflavin together with carnitine. Our results show that not all MADD patients have CoQ 10 deficiency. Based upon our data, riboflavin and carnitine may be the first-line treatment for MADD.

Batch experiments were carried out to investigate the stoichiometry and kinetics of microbial degradation of toluene under denitrifying conditions. The inoculum originated from a mixture of sludges from sewage treatment plants with alternating nitrification and denitrification. The culture was able to degrade toluene under anaerobic conditions in the presence of nitrate, nitrite, nitric oxide, or nitrous oxide. No degradation occurred in the absence of Noxides. The culture was also able to use oxygen, but ferric iron could not be used as an electron acceptor. In experiments with 14C-labeled toluene, 34% 4-8% of the carbon was incorporated into the biomass, while 53% 4-10% was recovered as t4CO2, and 6% + 2% remained in the medium as nonvolatile water soluble products. The average consumption of nitrate in experiments, where all the reduced nitrate was recovered as nitrite, was 1.3 :t: 0.2 mg of nitrate-N per mg of toluene. This nitrate reduction accounted for 70% of the electrons donated during the oxidation of toluene. When nitrate was reduced to nitrogen gas, the consumption was 0.7 4-0.2 nag per mg of toluene, accounting for 97% of the donated electrons. Since the ammonia concentration decreased during degradation, dissimilatory reduction of nitrate to ammonia was not the reductive process. The degradation of toluene was modelled by classical Monod kinetics. The maximum specific rate of degradation, k, was estimated to be 0.71 mg toluene per mg of protein per hour, and the Monod saturation constant, Ks, to be 0.2 mg toluene/1. The maximum specific growth rate,/~,~ax, was estimated to be 0.1 per hour, and the yield coefficient, Y, was 0.14 mg protein per mg toluene.

Objective. Zidovudine is an antiretroviral nucleoside analog reverse transcriptase inhibitor that induces mitochondrial myopathy by interfering with the replication of mitochondrial DNA (mtDNA). Because zidovudine inhibits thymidine kinases, the mechanism of mtDNA depletion may be related to an impairment of the de novo synthesis of pyrimidine nucleotides, which are required building blocks of mtDNA. This study was undertaken to determine whether mitochondrial myopathy is a class effect of antiretroviral nucleoside analogs, and whether the muscle disease can be prevented by treatment with uridine as a pyrimidine nucleotide precursor.

Coronary artery disease and its sequelae-ischemia, myocardial infarction, and heart failure-are leading causes of morbidity and mortality in man. Considerable effort has been devoted toward improving functional recovery and reducing the extent of infarction after ischemic episodes. As a step in this direction, it was found that the heart was significantly protected against ischemia -reperfusion injury if it was first preconditioned by brief ischemia or by administering a potassium channel opener. Both of these preconditioning strategies were found to require opening of a K ATP channel, and in 1997 we showed that this pivotal role was mediated by the mitochondrial ATP-sensitive K + channel (mitoK ATP ). This paper will review the evidence showing that opening mitoK ATP is cardioprotective against ischemiareperfusion injury and, moreover, that mitoK ATP plays this role during all three phases of the natural history of ischemia -reperfusion injury preconditioning, ischemia, and reperfusion. We discuss two distinct mechanisms by which mitoK ATP opening protects the heart-increased mitochondrial production of reactive oxygen species (ROS) during the preconditioning phase and regulation of intermembrane space (IMS) volume during the ischemic and reperfusion phases. It is likely that cardioprotection by ischemic preconditioning (IPC) and K ATP channel openers (KCOs) arises from utilization of normal physiological processes. Accordingly, we summarize the results of new studies that focus on the role of mitoK ATP in normal cardiomyocyte physiology. Here, we observe the same two mechanisms at work. In low-energy states, mitoK ATP opening triggers increased mitochondrial ROS production, thereby amplifying a cell signaling pathway leading to gene transcription and cell growth. In high-energy states, mitoK ATP opening prevents the matrix contraction that would otherwise occur during high rates of electron transport. MitoK ATP -mediated volume regulation, in turn, prevents disruption of the structure -function of the IMS and facilitates efficient energy transfers between mitochondria and myofibrillar ATPases. D

Insight into extracellular electron transfer of microorganisms is important for our understanding of electron-transport pathways in bioelectrochemical systems (e.g. biological fuel cells and microbial electrolysis cells), as well as for biogeochemical cycles, biocorrosion, and bioremediation. Two principal mechanisms for extracellular electron transfer have been proposed: 1) electroactive metabolites/secretions serve as mediators in an indirect electron-transfer process; 2) electrons transfer directly from the cells to the electrodes via either membrane cytochromes or electrically conductive pili. The latter process has been defined as direct electron transfer (DET) and has been studied intensely. It is well known that several microbes are capable of transforming a range of metal ions/minerals into nanoparticles, which remain bound to the cell membrane. However, little is understood about the role of such metallic nanoparticles in physiological electrontransfer processes, and important questions remain regarding the details of the mechanisms involved.

Heat-induced changes in photosystem I (PSI) have been studied in terms of rates of oxygen consumption using various donors (DCPIPH 2 , TMPD red and DAD red ), formation of photo-oxidized P700 and changes in Chl a fluorescence emission at 77 K. Linear heating of thylakoid membranes from 35 • C to 70 • C caused an enhancement in PSI-mediated electron transfer rates (DCPIPH 2 →MV) up to 55 • C. However, no change was observed in PSI rates when other electron donors were used (TMPD red and DAD red ). Similarly, Chl a fluorescence emission spectra at 77 K of heat-treated thylakoid membranes did not show any increase in peak at 735 nm, however, a significant decrease was observed as a function of temperature in the peaks at 685 and 694 nm. In DCMU-treated control thylakoid membranes maximum photo-oxidized P700 was generated at g = 2.0025. In heat-treated thylakoid membranes maximum intensity of photo-oxidized P700 signal was observed at ∼50-55 • C without DCMU treatment. The steady-state signal of the photo-oxidized P700 was studied in the presence of DCPIPH 2 and TMPD red as electron donors in DCMU-treated control and in 50 • C treated thylakoid membranes. We present here the first of such comparative study of PSI activity in terms of the rates of oxygen consumption and re-reduction kinetics of photo-oxidized P700 in the presence of different electron donors. It appears that the formation of the P700 + signal in heat-treated thylakoid membranes is due to an inhibited electron supply from PSII and not due to spillover or antenna migration.

We report the effect of average A-site cation radius on the structural, magnetic and electrical properties of electron doped manganite La 0.7 Ce 0.3 MnO 3 thin films. A site cation radius hr A i is varied systematically by partially replacing La C3 ions by smaller Y C3 ions in the parent compound. The carrier doping, i.e. the fraction of tetravalent Ce atoms at the A-site was kept at 30%. A series of La 0.7Kx Y x Ce 0.3 MnO 3 (xZ0, 0.05, 0.1, 0.15 and 0.25) thin films were prepared under identical conditions by using pulsed laser deposition technique. Metal-insulator transition temperature (T p ) and the ferromagnetic Curie temperature (T c ) are found to be decreasing significantly with increasing yttrium concentration, i.e. decreasing hr A i. The resistivity (r) at T p increases by one order of magnitude when the yttrium concentration is increased from xZ0 to 0.25, while magnetization decreases with decreasing hr A i. Magnetoresistance as measured under field of 1 T is significant near T c . Structural analysis reveals the films are having single phase and c-axis lattice parameter decreasing linearly as hr A i decreases. There is no marked difference in surface morphology of samples with different yttrium concentration. From EDX the Y:Ce:Mn ratio were consistent within 5% of the nominal composition. q

We investigate the survival probability ⌽(n,c) of particles performing a random walk on a two-dimensional lattice that contains static traps, which are randomly distributed with a concentration c, as a function of the number of steps n. ⌽(n,c) is analyzed in terms of a scaling ansatz, which allows us to locate quantitatively the crossover between the Rosenstock approximation ͑valid only at early times͒ and the asymptotic Donsker-Varadhan behavior ͑valid only at long times͒. While the existence of the crossover has been postulated before, its exact location has not been known. Our scaling hypothesis is based on the mean value of the quantity S n , the number of sites visited in an n-step walk. We make use of the idea of self-interacting random walks, and a ''slithering'' snake algorithm, available in the literature, and we are thus able to obtain accurate survival probability data indirectly by Monte Carlo simulation techniques. The crossover can now be determined by our method, and it is found to depend on a combination of c and n. It occurs at small ⌽(n,c) values, which is typically the case for large values of n.

Using cDNA microarray analysis, we previously identified a set of differentially expressed genes in primary breast tumors based on the status of estrogen and progesterone receptors. In the present study, we performed an integrated computer-assisted and manual search of potential estrogen response element (ERE) binding sites in the promoter region of these genes to characterize their potential to be regulated by estrogen receptors (ER). Publicly available databases were used to annotate the position of these genes in the genome and to extract a 5'flanking region 2 kb upstream to 2 kb downstream of the transcription start site for transcription binding site analysis. The search for EREs and other binding sites was performed using several publicly available programs. Overall, approximately 40% of the genes analyzed were potentially able to be regulated by estrogen via ER. In addition, 17% of these genes are located very close to other genes organized in a head-to-head orientation with less than 1.0 kb between their transcript units, sharing a bidirectional promoter, and could be classified as bidirectional gene pairs. Using quantitative real-time PCR, we further investigated the effects of 17β-estradiol and antiestrogens on the expression of the bidirectional gene pairs in MCF-7 breast cancer cells. Our results showed that some of these gene pairs, such as TXNDC9/ EIF5B, GALNS/TRAPPC2L, and SERINC1/PKIB, are modulated by 17β-estradiol via ER in MCF-7 breast cancer cells. Here, we also characterize the promoter region of potential ER-regulated genes and provide new information on the transcriptional regulation of bidirectional gene pairs.

The effects of paraquat on rat brain were studied. Activities of complex I (NADH: ubiquinone oxidoreductase) in mitochondrial electron transport system, lipid peroxidation and the amount of catecholamines in rat brain were measured after acute paraquat exposure. Complex I activities were significantly lower and lipid peroxides were higher in the brains of a paraquat-treated group than in those of a control group. Lipid peroxide in rat serum, however, did not increase after paraquat exposure. A study of the time dependency of paraquat effects disclosed that mitochondrial complex I activities in rat brain as well as those in rat lung and liver gradually decreased prior to the appearance of respiratory dysfunction. As compared to controls, the dopamine in rat striatum was significantly lower in the paraquat-treated group. These results suggest that paraquat after crossing the blood-brain barrier might be reduced to the radical in rat brain, which may damage the brain tissue, especially dopaminergic neurons in striatum. We therefore propose that cerebral damage should be taken into consideration on paraquat exposure. Patients may therefore need to be followed up after exposure to high doses of paraquat.

Fast ignition requires a precise knowledge of fast electron propagation in a dense hydrogen plasma. In this context, a dedicated HiPER (High Power laser Energy Research) experiment was performed on the VULCAN laser facility where the propagation of relativistic electron beams through cylindrically compressed plastic targets was studied. In this paper, we characterize the plasma parameters such as temperature and density during the compression of cylindrical polyimide shells filled with CH foams at three different initial densities. X-ray and proton radiography were used to measure the cylinder radius at different stages of the compression. By comparing both diagnostics results with 2D hydrodynamic simulations, we could infer densities from 2 to 11 g=cm 3 and temperatures from 30 to 120 eV at maximum compression at the center of targets. According to the initial foam density, kinetic, coupled (sometimes degenerated) plasmas were obtained. The temporal and spatial evolution of the resulting areal densities and electrical conductivities allow for testing electron transport in a wide range of configurations. V

The cofactor composition and electron-transfer kinetics of the reaction center (RC) from a magnesium chelatase (bchD) mutant of Rhodobacter sphaeroides were characterized. In this RC, the special pair (P) and accessory (B) bacteriochlorophyll (BChl)-binding sites contain Zn-BChl rather than BChl a. Spectroscopic measurements reveal that Zn-BChl also occupies the H sites that are normally occupied by bacteriopheophytin in wild type, and at least 1 of these Zn-BChl molecules is involved in electron transfer in intact Zn-RCs with an efficiency of >95% of the wild-type RC. The absorption spectrum of this Zn-containing RC in the near-infrared region associated with P and B is shifted from 865 to 855 nm and from 802 to 794 nm respectively, compared with wild type. The bands of P and B in the visible region are centered at 600 nm, similar to those of wild type, whereas the H-cofactors have a band at 560 nm, which is a spectral signature of monomeric Zn-BChl in organic solvent. The Zn-BChl H-cofactor spectral differences compared with the P and B positions in the visible region are proposed to be due to a difference in the 5th ligand coordinating the Zn. We suggest that this coordination is a key feature of protein-cofactor interactions, which significantly contributes to the redox midpoint potential of H and the formation of the charge-separated state, and provides a unifying explanation for the properties of the primary acceptor in photosystems I (PS1) and II (PS2). magnesium chelatase mutant ͉ photosynthetic bacterial reaction center ͉ photosystems I and II ͉ protein-cofactor interaction

Cytochrome b561 family was characterized by the presence of ''b561 core domain'' that forms a transmembrane four helix bundle containing four totally conserved His residues, which might coordinate two heme b groups. We conducted BLAST and PSI-BLAST searches to obtain insights on structure and functions of this protein family. Analyses with CLUSTAL W on b561 sequences from various organisms showed that the members could be classified into 7 subfamilies based on characteristic motifs; groups A (animals/neuroendocrine), B (plants), C (insects), D (fungi), E (animals/TSF), F (plants + DoH), and G (SDR2). In group A, both motif 1, {FN(X)HP(X) 2 M(X) 2 G(X) 5 G(X)ALLVYR}, and motif 2, {YSLHSW(X)G}, were identified. These two motifs were also conserved in group B. There was no significant features characteristic to groups C and D. A modified version of motif 1, {LFSWHP(X) 2 M(X) 3 F(X) 3 M(X)EAIL(X)SP(X) 2 SS}, was found in group E with a high degree of conservation. Both motif 3, {DP(X)WFY(L)H(X) 3 Q}, and motif 4, {K(X)R(X)YWN(X)YHH(X) 2 G(R/Y)} ,were found in group F at different regions from those of motifs 1 and 2. The ''DoH'' domain common to the NH 2 -terminal region of dopamine h-hydroxylase was found to form fusion proteins with the b561 core domains in groups F and G. Based on these results, we proposed a hypothesis regarding structures and functions of the 7 subfamilies of cytochrome b561. D

Stable and switchable polarization of ferroelectric materials opens a possibility to electrically control their functional behavior. A particularly promising approach is to employ ferroelectric tunnel junctions where the polarization reversal in a ferroelectric barrier changes the tunneling current across the junction. Here, we demonstrate the reproducible tunneling electroresistance effect using a combination of Piezoresponse Force Microscopy (PFM) and Conducting Atomic Force Microscopy (C-AFM) techniques on nanometer-thick epitaxial BaTiO 3 single crystal thin films on SrRuO 3 bottom electrodes. Correlation between ferroelectric and electronic transport properties is established by the direct nanoscale visualization and control of polarization and tunneling current in BaTiO 3 films. The obtained results show a change in resistance by about two orders of magnitude upon polarization reversal on a lateral scale of 20 nm at room temperature.

We present a scheme for high sensitivity charge detection in the integer quantum Hall regime using two point contacts in a series. The setup is an electronic analog of an optical Fabry-Perot interferometer. We show that for small transmission through the point contacts the sensitivity of the interferometer is very high due to multiple reflections at the point contacts. The sensitivity can be further enhanced twice by using electrons in spin entangled state. We show that for point contacts having different reflection probabilities, the interferometer can be tuned for the quantum limited measurement.

We calculate the d.c.-current of a semiconductor superlattice in the hopping conduction picture. Electronic transport in this regime is described by hopping transitions between the partially localized Wannier–Stark states. In our numerical model we start from the exact wavefunctions of the superlattice and include both impurity and acoustic phonon scattering. We then obtain the electron drift velocity by considering the

The process of dark-induced senescence in plants is relatively poorly understood, but a functional electron-transfer flavoprotein/electron-transfer flavoprotein:ubiquinone oxidoreductase (ETF/ETFQO) complex, which supports respiration during carbon starvation, has recently been identified. Here, we studied the responses of Arabidopsis thaliana mutants deficient in the expression of isovaleryl-CoA dehydrogenase and 2-hydroxyglutarate dehydrogenase to extended darkness and other environmental stresses. Evaluations of the mutant phenotypes following carbon starvation induced by extended darkness identify similarities to those exhibited by mutants of the ETF/ETFQO complex. Metabolic profiling and isotope tracer experimentation revealed that isovaleryl-CoA dehydrogenase is involved in degradation of the branched-chain amino acids, phytol, and Lys, while 2-hydroxyglutarate dehydrogenase is involved exclusively in Lys degradation. These results suggest that isovaleryl-CoA dehydrogenase is ...

Physical electrochemistry has undergone a remarkable evolution over the last few decades, integrating advanced techniques and theory from solid state and surface physics. Single-crystal electrode surfaces have been a core notion, opening for scanning tunnelling microscopy directly in aqueous electrolyte (in situ STM). Interfacial electrochemistry of metalloproteins is presently going through a similar transition. Electrochemical surfaces with thiol-based promoter molecular monolayers (SAMs) as biomolecular electrochemical environments and the biomolecules themselves have been mapped with unprecedented resolution, opening a new area of single-molecule bioelectrochemistry. We consider first in situ STM of small redox molecules, followed by in situ STM of thiol-based SAMs as molecular views of bioelectrochemical environments. We then address electron transfer metalloproteins, and multi-centre metalloenzymes including applied single-biomolecular perspectives based on metalloprotein/metallic nanoparticle hybrids.

The nitric-oxide synthases (NOS, EC 1.14.13.39) are modular enzymes containing attached flavoprotein and heme (NOSoxy) domains. To generate nitric oxide (NO), the NOS FMN subdomain must interact with the NOSoxy domain to deliver electrons to the heme for O 2 activation during catalysis. The molecular basis and how the interaction is regulated is unclear. We explored the role of eight positively charged residues that create an electropositive patch on NOSoxy in enabling the electron transfer by incorporating mutations that neutralized or reversed their individual charges. Stopped-flow and steady-state experiments revealed that individual charges at Lys 423 , Lys 620 , and Lys 660 were the most important in enabling heme reduction in nNOS. Charge reversal was more disruptive than neutralization in all cases, and the effects on heme reduction were not due to a weakening in the thermodynamic driving force for heme reduction. Mutant NO synthesis activities displayed a complex pattern that could be simulated by a global model for NOS catalysis. This analysis revealed that the mutations impact the NO synthesis activity only through their effects on heme reduction rates. We conclude that heme reduction and NO synthesis in nNOS is enabled by electrostatic interactions involving Lys 423 , Lys 620 , and Lys 660 , which form a triad of positive charges on the NOSoxy surface. A simulated docking study reveals how electrostatic interactions of this triad can enable an FMN-NOSoxy interaction that is productive for electron transfer.

Mitochondrial dysfunction (primary or secondary) is detrimental to intermediary metabolism. Therapeutic strategies to treat/prevent mitochondrial dysfunction could be valuable for managing metabolic and age-related disorders. Here, we review strategies proposed to treat mitochondrial impairment. We then concentrate on redox-active agents, with mild-redox potential, who shuttle electrons among specific cytosolic or mitochondrial redox-centers. We propose that specific redox agents with mild redox potential (À0.1 V; 0.1 V) improve mitochondrial function because they can readily donate or accept electrons in biological systems, thus they enhance metabolic activity and prevent reactive oxygen species (ROS) production. These agents are likely to lack toxic effects because they lack the risk of inhibiting electron transfer in redox centers. This is different from redox agents with strong negative (À0.4 V; À0.2 V) or positive

We implement and compare two theoretical models for stationary electron transport in quantum cascade lasers and Stark ladders. The first one, the nonequilibrium Green's function method is a very general scheme to include coherent quantum mechanics and incoherent scattering with phonons and device imperfections self-consistently. However, it is numerically very demanding and cannot be used for systematic device parameter scans. For this reason, we also implement the approximate, numerically efficient ensemble Monte Carlo method and assess its applicability on the above mentioned transport problems. We identify a transport regime in which results of both methods quantitatively agree. In this regime, the ensemble Monte Carlo method is well suited to propose design improvements.

Modern optoelectronic devices, such as light-emitting diodes, fieldeffect transistors and organic solar cells require well controlled motion of charges for their efficient operation. The understanding of the processes that determine charge transport is therefore of paramount importance for designing materials with improved structure-property relationships. Before discussing different regimes of charge transport in organic semiconductors, we present a brief introduction into the conceptual framework in which we interpret the relevant photophysical processes. That is, we compare a molecular picture of electronic excitations against the Su-Schrieffer-Heeger semiconductor band model. After a brief description of experimental techniques needed to measure charge mobilities, we then elaborate on the parameters controlling charge transport in technologically relevant materials. Thus, we consider the influences of electronic coupling between molecular units, disorder, polaronic effects and space charge. A particular focus is given to the recent progress made in understanding charge transport on short time scales and short length scales. The mechanism for charge injection is briefly addressed towards the end of this chapter. Keywords Charge carrier mobility Á Charge transport Á Organic semiconductors Á Molecular model Á Gaussian disorder model Á SSH model Á Organic optoelectronics Contents

BSb films were deposited onto fused silica substrates by coevaporating B and Sb from appropriate boats. Optical studies indicated an indirect band gap of $0.59 eV. The films thus prepared were characterized by measuring X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) studies. XPS studies indicated the ratio of B:Sb $1. XRD indicated the reflections from (1 0 1), (1 1 1), (1 1 2), (3 3 0), (3 3 1) and (3 2 3) planes of zinc blende BSb. FTIR spectra indicated the peaks for B-B, B-O, B-Sb vibration modes. A strong peak located at $151 cm À1 for B-Sb modes dominated the Raman spectra. Electrical resistivity was measured for B-Sb films in the temperature range of 100-353 K. Electron transport process was seen to be governed by Mott's hopping when complete temperature dependence of the conductivity is considered. r

Both light itself and excitation pressure have been implicated as the environmental signal that stimulates interchange of the two forms of the D1 protein of photosystem II (PS II) in Synechococcus sp. strain PCC 7942. We sought an explanation for conflicting reports regarding the role of photosynthetic electron transport in regulation of psbA expression and D1 interchange. Inhibitors that block at different points in the photosynthetic electron transport chain were administered and the effect on expression of psbAII, which encodes the high-light-induced form II of D1, was examined by measuring changes in transcript levels and in the activities of reporter enzymes. Both 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of PSII, and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), an inhibitor of the cytochrome b6/f complex, prevented high-light-induced increase in β-galactosidase activity from a psbAII::lacZ gene fusion when added at a concentration that completely inhibits photosynthetic electron transport (1 μM). The same effect was observed for luciferase activity from transcriptional and translational fusions of psbAII to the luxAB genes from Vibrio harveyi. DCMU (1 μM) arrested luciferase expression at low-light levels – thus eliminating the high light response – whereas a sublethal concentration (50 nM), which reduces electron transport by 50%, had intermediate effects on psbAII-driven luciferase activity. However, psbAII transcript levels, monitored by northern blot analysis, were not altered by electron transport inhibitors, either at low-light intensity or following a high-light exposure. The suppressive effect of DCMU on expression of reporter enzymes was not restricted to the high-light response of psbAII-driven reporter systems, but was also observed using an isopropyl-(-d)-thiogalactopyranoside (IPTG)-inducible trc promoter fused to luxAB. This construct only marginally responded to IPTG addition when DCMU was present. Thus, blocking electron transport in Synechococcus affects the translation machinery in a general way, and the use of electron transport inhibitors is of limited value when focusing on specific redox regulation of D1 protein synthesis or degradation.

Photosystem I and Photosystem II activities, as well as polypeptide content of chlorophyll (Chl)-protein complexes were analyzed in mesophyll (M) and bundle sheath (BS) chloroplasts of maize (Zea mays L.) growing under moderate and very low irradiance. This paper discusses the application of two techniques: mechanical and enzymatic, for separation of M and BS chloroplasts. The enzymatic isolation method resulted in depletion of polypeptides of oxygen evolving complex (OEC) and aCF1 subunit of coupling factor; D1 and D2 polypeptides of PSII were reduced by 50%, whereas light harvesting complex of photosystem II (LHCII) proteins were still detectable. Loss of PSII polypeptides correlated with the decreasing of Chl fluorescence measured at room temperature. Using mechanical isolation of chloroplasts from BS cells, all tested polypeptides could be detected. We found a total lack of O 2 evolution in BS chloroplasts, but dichlorophenolindophenol (DCPIP) was photoreduced. PSI activity of chloroplasts isolated from 14-and 28-day-old plants was similar in BS chloroplasts in moderate light (ML), but in low light (LL) it was reduced by about 20%. PSI and PSII activities in M chloroplasts of plants growing in ML decreased with aging of plants. In older LL-grown plants, activities of both photosystems were higher than those observed in chloroplasts from ML-grown plants.

In order to clarify the response of antioxidant systems in various cellular organelles to photo-oxidative stress, the activities of superoxide dismutase (SOD) and enzymes of the ascorbateglutathione (AsA-GSH) cycle were investigated in chloroplasts, mitochondria and cytosol of cucumber leaves subjected to methyl viologen (MV) treatment. Photo-oxidation by MV resulted in significant reductions in net photosynthetic rate (Pn) and increases in the ratio of the quantum efficiency of photosystem II (PSII), U PSII to that of the quantum efficiency of CO 2 fixation (U CO 2), followed by increased activities of SOD, and a general increase of AsA-GSH cycle enzymes in chloroplasts, mitochondria and cytosol. These increases were however, most significant in chloroplasts. There were also significant increases in dehydroascorbate (DHA), reduced glutathione (GSH), and oxidized glutathione (GSSG) except that the content of ascorbate (AsA) in chloroplasts and cytosol was slightly decreased and little effected, respectively. However, GSSG in mitochondria and GSH in cytosol were little influenced by the MV treatment. The activity of ascorbate oxidase (AO) in these organelles was independent of the MV treatment while the activity of L-galactono-1,4lactone dehydrogenase (GLDH) in mitochondria was slightly inhibited by MV treatment. These results indicate that disturbance of electron transport in chloroplasts by MV influenced the metabolism of whole cell by a crosstalk signaling system and that the AsA-GSH cycle played a primary role in sustaining the levels of AsA.

The unicellular alga Dunaliella salina is the most interesting cell factory for the commercial production of bcarotene because this species accumulates carotenoids to high concentrations. Nevertheless, little is known about the underlying mechanisms of carotenoid accumulation. Here, we review the regulatory mechanisms involved in b-carotene overproduction in D. salina. The potential roles of reactive oxygen species and the plastoquinone redox state in signal sensing are discussed, together with available evidence on transcriptional and (post)translational regulation. Moreover, future directions that might further our knowledge in this area are given. Ultimately, a better understanding of the regulatory mechanisms involved in b-carotene overproduction will facilitate innovative production of specific carotenoids and other products in D. salina and in related organisms.

In the past 20 years a variety of electronic markets have been setup for the allocation of capacities in road transportation. A lthough, inefficiencies and cost pressures are high, the electronic markets have not succeeded so far. In this paper we will give an overview of the so-called electronic transportation exchanges and analyze the factors that were involved in the repeated failures. By using a multi-layer framework which integrates established research approaches for interorganizational systems (IOS) we argue that the failures provide valuable insights for the configuration of electronic commmerce systems in general and in particular for the transportation exchanges that are currently emerging on the Internet.

The radical cation P840" was studied in frozen suspensions of Chlorobium limicolu f. sp. thiosulphatophilum membranes using ENDOR and Special TRIPLE spectroscopies. The spectra show that P840" arises from a bacteriochlorophyll a 'special' pair with a highly symmetrical distribution of electron spin density between the constituent bacteriochlorophylls. Special TRIPLE spectroscopy has resolved the separate contributions of the two halves of the pair and revealed small deviations from a 1 : 1 electron spin density distribution. Nevertheless P840" appears to come the closest yet to the symmetrical 'dimer' originally proposed for the structure of the primary donor radical cation (P870") in purple non-sulphur photosynthetic bacteria.

Previous studies have suggested that the conductive pili of Geobacter sulfurreducens are essential for extracellular electron transfer to Fe(III) oxides and for optimal long-range electron transport through current-producing biofilms. The KN400 strain of G. sulfurreducens reduces poorly crystalline Fe(III) oxide more rapidly than the more extensively studied DL-1 strain. Deletion of the gene encoding PilA, the structural pilin protein, in strain KN400 inhibited Fe(III) oxide reduction. However, low rates of Fe(III) reduction were detected after extended incubation (>30 days) in the presence of Fe(III) oxide. After seven consecutive transfers, the PilA-deficient strain adapted to reduce Fe(III) oxide as fast as the wild type. Microarray, whole-genome resequencing, proteomic, and gene deletion studies indicated that this adaptation was associated with the production of larger amounts of the c-type cytochrome PgcA, which was released into the culture medium. It is proposed that the ...

The interest in organic materials for use in organic light-emitting diodes (OLEDs) began with the pioneering report of efficient green electroluminescence from Alq 3 , tris(quinolin-8-olato)aluminum(III), by Tang and Van Slyke [C.W. Tang, S.A. Van Slyke, Appl. Phys. Lett. 51 ]. After more than 20 years of intense research and development in OLEDs, Alq 3 continues to be a widely used electroluminescent material in OLED technology. Alq 3 is used in the electron-transport and/or electron-injecting layer in multilayer device structures and also as an effective host material for various dyes. Much is known about the properties of this metal chelate complex, yet much remains unknown despite numerous studies. In recent years, five crystalline phases (a, b, c, d, and e) of Alq 3 have been identified. In the present report, a combined structural, thermal, and spectroscopic (Raman, fluorescence, and nuclear magnetic resonance) analysis of different crystalline phases of Alq 3 is presented.

The time dependence of photobleaching of photosynthetic pigments under high light illumination of isolated spinach thylakoid membranes at 22 and 4 8C was investigated. At 22 8C, the bleaching at 678, 472 and 436 nm was prominent but lowering the temperature up to 4 8C during illumination prevented the pigments from bleaching almost completely. The accelerating effect on pigment photobleaching by the presence of 3-(3,4 dichlorophenyl)-1,1dimethyl-urea)-(DCMU), a well-known inhibitor of the electron transport and known to prevent photosystem I (PSI) and photosystem II (PSII) against photoinhibitory damage, was also suppressed at low temperature. At 22 8C in the presence and absence of DCMU, the decrease of the absorption at 678 and 472 nm was accompanied by a shift to the shorter wavelengths. To check the involvement of reactive oxygen species in the process, pigment photobleaching was followed in anaerobiosis. The effects of the three different environmental factors-light, temperature and DCMU-on the dynamics of photobleaching are discussed in terms of different susceptibility of the main pigment-protein complexes to photoinhibition. ᮊ

Although the central role of the phagocytic NADPH oxidase in mediating bacterial killing has long been appreciated, this sophisticated enzyme complex serves various other important functions. This Perspective focuses on these underappreciated roles of phagocytic NADPH oxidase, highlighting recent work implicating reactive oxygen species in triggering an unconventional form of cell death.

An ab initio Green's function study of the electron transport properties of the selected metal-porphyrin complexes has been performed. Transmission spectra and current-voltage dependence have been calculated for the porphyrin molecule located between gold electrodes in the presence of interaction with metal atoms, which are most common in biochemistry (Fe(II), Fe(III), Mn(II), and Zn(II)). It was shown that the estimated Fermi level almost coincides with the LUMO level of Fe(II)-porphyrin and Fe(III)-porphyrin, resulting in significant conductance at small voltage biases. Conductance of Mn(II)-porphyrin and Zn(II)-porphyrin are much lower, and decrease from Mn to Zn. It was confirmed that performing spin-unrestricted calculations is essential to account splitting of the original molecular orbitals levels. Preformed calculations demonstrate the principal possibility of experimental realization of porphyrin based nanosensors.

The reflection and transmission amplitudes of waves in disordered multimode waveguides are studied by means of numerical simulations based on the invariant embedding equations. In particular, we analyze the influence of surface-type disorder on the behavior of the ensemble average and fluctuations of the reflection and transmission coefficients, reflectance, transmittance, and conductance. Our results show anomalous effects stemming from the combination of mode dispersion and rough surface scattering: For a given waveguide length, the larger the mode transverse momentum is, the more strongly is the mode scattered. These effects manifest themselves in the mode selectivity of the transmission coefficients, anomalous backscattering enhancement, and speckle pattern both in reflection and transmission, reflectance and transmittance, and also in the conductance and its universal fluctuations. It is shown that, in contrast to volume impurities, surface scattering in quasione-dimensional structures (waveguides) gives rise to the coexistence of the ballistic, diffusive, and localized regimes within the same sample.

The measured peak shape and intensity of the photoemitted signal in X-ray photoelectron spectroscopy (XPS) experiments (elastic and inelastic parts included) are strongly correlated, through electron-transport theory, with the depth distribution of photoelectron emitters within the analyzed surface. This is the basis of so-called XPS peakshape analysis (also known as the Tougaard method) for non-destructive determination of compositional in-depth (up to 6-8 nm) profiles. This review describes the theoretical basis and reliability of this procedure for quantifying amounts and distributions of material within a surface. The possibilities of this kind of analysis are illustrated with several case examples related to the study of the initial steps of thin-film growth and the modifications induced in polymer surfaces after plasma treatments.