Single-walled carbon nanotubes (SWCNTs) deposits on glassy carbon and pyrolytic graphite electrodes have dramatically enhanced the direct electron transfer of the multihemic nitrite reductase from Desulfovibrio desulfuricans ATCC 27774, enabling a 10-fold increase in catalytic currents. At optimal conditions, the sensitivity to nitrite and the maximum current density were 2.4 +/- 0.1 A L mol(-1) cm(-2) and 1500 mu A cm(-2), respectively. Since the biosensor performance decreased over time, laponite clay and electropolymerized amphiphilic pyrrole were tested as protecting layers. Both coating materials increased substantially the bioelectrode stability, which kept about 90% and 60% of its initial sensitivity to nitrite after 20 and 248 days, respectively.

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Electron transfer proteins and redox enzymes containing paramagnetic redox centers with different relaxation rates are widespread in nature. Despite both the long distances and chemical paths connecting these centers, they can present weak magnetic couplings produced by spin-spin interactions such as dipolar and isotropic exchange. We present here a theoretical model based on the Bloch-Wangsness-Redfield theory to analyze the dependence with temperature of EPR spectra of interacting pairs of spin 1/2 centers having different relaxation rates, as is the case of the molybdenum-containing enzyme aldehyde oxidoreductase from Desulfovibrio gigas. We analyze the changes of the EPR spectra of the slow relaxing center (Mo(V)) induced by the faster relaxing center (FeS center). At high temperatures, when the relaxation time T(1) of the fast relaxing center is very short, the magnetic coupling between centers is averaged to zero. Conversely, at low temperatures when T(1) is longer, no modulation of the coupling between metal centers can be detected.

No abstract is available for this item.

The catalytic mechanism of nitrate reduction by periplasmic nitrate reductases has been investigated using theoretical and computational means. We have found that the nitrate molecule binds to the active site with the Mo ion in the +6 oxidation state. Electron transfer to the active site occurs only in the proton-electron transfer stage, where the Mo(V) species plays an important role in catalysis. The presence of the sulfur atom in the molybdenum coordination sphere creates a pseudo-dithiolene ligand that protects it from any direct attack from the solvent. Upon the nitrate binding there is a conformational rearrangement of this ring that allows the direct contact of the nitrate with Mo(VI) ion. This rearrangement is stabilized by the conserved methionines Met141 and Met308. The reduction of nitrate into nitrite occurs in the second step of the mechanism where the two dimethyl-dithiolene ligands have a key role in spreading the excess of negative charge near the Mo atom to make it available for the chemical reaction. The reaction involves the oxidation of the sulfur atoms and not of the molybdenum as previously suggested. The mechanism involves a molybdenum and sulfur-based redox chemistry instead of the currently accepted redox chemistry based only on the Mo ion. The second part of the mechanism involves two protonation steps that are promoted by the presence of Mo(V) species. Mo(VI) intermediates might also be present in this stage depending on the availability of protons and electrons. Once the water molecule is generated only the Mo(VI) species allow water molecule dissociation, and, the concomitant enzymatic turnover.

Selective interaction between Crystal Violet Lactone and Fe(3+)/Fe(2+) in methanol leads to a reversible ionochromic colour change. This interaction can be controlled electrochemically, in order to achieve reversible colour changes with high contrast between colourless and dark blue solutions. The presented system is proposed as an alternative electrochromic solution. (C) 2009 Elsevier Ltd. All rights reserved.

Electrospun cellulose-based nano and microfibers and a nematic liquid crystal are used to assemble an electro-optical (EO) light-scattering device that shows enhanced characteristics when compared to similar devices. Based on the controlled scattering of light in the composite system, the device can achieve light transmission coefficients tunable from 1% up to around 89%. Simulation of the EO behavior indicates that the roughness of the polymer-liquid crystal interface is crucial for the optical performance of the device.

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The multicopper enzyme nitrous oxide reductase (N 2OR) catalyzes the final step of denitrification, the two-electron reduction of N 2O to N 2. This enzyme is a functional homodimer containing two different multicopper sites: CuA and CuZ. CuA is a binuclear copper site that transfers electrons to the tetranuclear copper sulfide CuZ, the catalytic site. In this study, Pseudomonas nautica cytochrome c 552 was identified as the physiological electron donor. The kinetic data show differences when physiological and artificial electron donors are compared [cytochrome vs methylviologen (MV)]. In the presence of cytochrome c 552, the reaction rate is dependent on the ET reaction and independent of the N 2O concentration. With MV, electron donation is faster than substrate reduction. From the study of cytochrome c 552 concentration dependence, we estimate the following kinetic parameters: K m c 552 = 50.2 +/- 9.0 muM and V max c 552 = 1.8 +/- 0.6 units/mg. The N 2O concentration dependence indicates a K mN 2 O of 14.0 +/- 2.9 muM using MV as the electron donor. The pH effect on the kinetic parameters is different when MV or cytochrome c 552 is used as the electron donor (p K a = 6.6 or 8.3, respectively). The kinetic study also revealed the hydrophobic nature of the interaction, and direct electron transfer studies showed that CuA is the center that receives electrons from the physiological electron donor. The formation of the electron transfer complex was observed by (1)H NMR protein-protein titrations and was modeled with a molecular docking program (BiGGER). The proposed docked complexes corroborated the ET studies giving a large number of solutions in which cytochrome c 552 is placed near a hydrophobic patch located around the CuA center.

No abstract is available for this item.

Metalloenzymes control enzymatic activity by changing the characteristics of the metal centers where catalysis takes place. The conversion between inactive and active states can be tuned by altering the coordination number of the metal site, and in some cases by an associated conformational change. These processes will be illustrated using heme proteins (cytochrome c nitrite reductase, cytochrome c peroxidase and cytochrome cd1 nitrite reductase), non-heme proteins (superoxide reductase and [NiFe]-hydrogenase), and copper proteins (nitrite and nitrous oxide reductases) as examples. These examples catalyze electron transfer reactions that include atom transfer, abstraction and insertion.

Electrochromic materials are characterized by their colour changes upon applied voltage. Colour can mean many things: a certain kind of light, its effect on the human eye, or the result of this effect in the mind of the viewer. Since the electrochromic materials are developed towards real life applications it is relevant to characterize them with the usual commercial colour standards. A colorimetric study of electrogenerated Prussian blue and electrogenerated polymers based on salen-type complexes of Cu(II), Ni(II) and Pd(H) deposited over transparent flexible electrodes of polyethylene terephthalate coated with indium tin oxide (PET/ITO electrodes) was carried out using the CIELAB coordinates. A cuvette with a designed adapter to allow potentiostatic control was placed on an integrating sphere installed in the sample compartment of a spectrophotometer to run the colorimetric measurements. The colour evolution in situ was measured through the transmittance of the films by potentiostatic control. Chronocoutometry/chronoabsorptometry was used to evaluate maximum coloration efficiencies for the coloration step: 184 (Pd), 161 (Cu) and 83 cm(2)/C (Ni) and for bleaching: 199 (Pd), 212 (Cu) and 173 cm(2)/C (Ni) of the Pd, Cu and Ni polymer films, respectively. The Prussian Blue/Prussian White states over the PET/ITO films were relatively reversible while the reversibility and stability of the polymers based on the metals salen-type complexes depends on the metal, Pd being the most stable. (c) 2008 Elsevier B.V. All rights reserved.

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Recent progress in global sequence and microarray data analysis has revealed the increasing complexity of the human transcriptome. Alternative splicing generates a huge diversity of transcript variants and disruption of splicing regulatory networks is emerging as an important contributor to various diseases, including cancer. Current efforts to establish the dynamic repertoire of transcripts that are generated in health and disease are showing that many cancer-associated alternative-splicing events occur in the absence of mutations in the affected genes. A growing body of evidence reveals changes in splicing-factor expression that correlate with cancer development, progression and response to therapy. Here, we discuss how recent links between cancer and altered expression of proteins implicated in splicing regulation are bringing the splicing machinery to the fore as a potential target for anticancer treatment.

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