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Cyclic voltammetry is a particularly useful tool for characterizing charge accumulation in conductive materials. A simple model is presented to evaluate proton transport effects on charge storage in conductive materials associated with a redox process coupled with proton insertion in the bulk material from an aqueous buffered solution, a situation frequently encountered in metal oxide materials. The interplay between proton transport inside and outside the materials is described using a formulation of the problem through introduction of dimensionless variables that allows defining the minimum number of parameters governing the cyclic voltammetry response with consideration of a simple description of the system geometry. This approach is illustrated by analysis of proton insertion in a mesoporous TiO2 film.

RESUMEN

This contribution highlights correlation between the surface concentration of a chemisorbed organophosphorous probe (flavin mononucleotide) and the relative hydroxyl surface coverage of nanostructured ITO electrodes, which can be tuned during post-deposition reductive annealing. The resulting modified electrodes are very stable in aqueous solution, highly hydrophilic and fully-accessible to the bulk solution.

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The formation of 8-SH-cGMP from the reaction between hydrogen sulfide and 8-nitro-guanosine-3',5'-cyclic monophosphate in the presence of thiols does not take place by nucleophilic attack of the hydrosulfide anion, as previously proposed, but first involves the formation of reactive species containing sulfane sulfur, like persulfides.

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UV-visible absorption spectroelectrochemistry elucidated the different redox behaviours of Fe(III)- and Co(III)-mimochrome VI artificial enzymes, adsorbed on mesoporous conductive films of ITO. The reduction of the ferric complex was rapid and reversible, while the cobaltic complex exhibited irreversible processes probably related to multiple coordination states.

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AIMS: Exploitation of natural biodiversity in species Pycnoporus coccineus and Pycnoporus sanguineus to screen for a new generation of laccases with properties suitable for the lignin-processing sector. METHODS AND RESULTS: Thirty strains originating from subtropical and tropical environments, mainly isolated from fresh specimens collected in situ, were screened for laccase activity. On the basis of levels of enzyme activity and percentage of similarity between protein sequences, the laccases from strains BRFM 938, BRFM 66 and BRFM 902 were selected for purification and characterization. Each BRFM 938, BRFM 66 and BRFM 902 laccase gene encoded a predicted protein of 518 amino acids; the three deduced proteins showed 68.7-97.5% similarity with other Polyporale laccases. The three laccases (59.5-62.9 kDa with 7-10% carbohydrate content) had high redox potentials (0.72-0.75 V vs normal hydrogen electrode at pH 6), remained highly stable up to 75-78 degrees C and at pH 5-7 mixtures, and were resistant to methyl and ethyl alcohols, acetonitrile and dimethylsulfoxide at concentrations as high as 50% (v/v). The best laccase-1-hydroxybenzotriazole systems permitted almost 100% of various polyphenolic dye decolourization and oxidation of adlerol and veratryl alcohol. CONCLUSIONS: The three laccases showed complementary biochemical features. BRFM 938 laccase had the highest thermo- and pH stability, catalytic efficiency towards 2,2'-azino-bis-[3-ethylthiazoline-6-sulfonate] and resistance to alcoholic solvents. BRFM 66 laccase had the highest rates of dye decolourization and oxidation of nonphenolic compounds. SIGNIFICANCE AND IMPACT OF THE STUDY: This study identified P. coccineus and P. sanguineus as outstanding producers of high redox potential laccases, easy to purify and scale-up for industrial production. Three new laccases proved to be suitable models for white biotechnology processes and for further molecular breeding to create a new generation of tailor-made enzymes.

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BjFixL from Bradyrhizobium japonicum is a heme-based oxygen sensor implicated in the signaling cascade that enables the bacterium to adapt to fluctuating oxygen levels. Signal transduction is initiated by the binding of O(2) to the heme domain of BjFixL, resulting in protein conformational changes that are transmitted to a histidine kinase domain. We report structural changes of the heme and its binding pocket in the Fe(II) deoxy and Fe(III) met states of the wild-type BjFixLH oxygen sensor domain and four mutants of the highly conserved residue arginine 220. UV-visible, electron paramagnetic resonance, and resonance Raman spectroscopies all showed that the heme iron of the R220H mutant is unexpectedly six-coordinated at physiological pH in the Fe(III) state but undergoes pH- and redox-dependent coordination changes. This behavior is unprecedented for FixL proteins, but is reminiscent of another oxygen sensor from E. coli, EcDos. All mutants in their deoxy states are five-coordinated Fe(II), although we report rupture of the residue 220-propionate 7 interaction and structural modifications of the heme conformation as well as propionate geometry and flexibility. In this work, we conclude that part of the structural reorganization usually attributed to O(2) binding in the wild-type protein is in fact due to rupture of the Arg220-P7 interaction. Moreover, we correlate the structural modifications of the deoxy Fe(II) states with k(on) values and conclude that the Arg220-P7 interaction is responsible for the lower O(2) and CO k(on) values reported for the wild-type protein.

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