A Comparative Study between Hydrogen Peroxide Amperometric Biosensors Based on Different Peroxidases Wired by Os-Polymer: Applications in Water, Milk and Human Urine

In the last few years, hydrogen peroxide [...

A Comparative Study between Hydrogen Peroxide Amperometric Biosensors Based on Different Peroxidases Wired by Os-Polymer: Applications in Water, Milk and Human Urine

In the last few years, hydrogen peroxide [...

Voltammetric study of the adsorbed thermophilic plastocyanin from Phormidium laminosum up to 90 °c

Redox thermodynamics and kinetics of plastocyanin from Phormidium laminosum, and of azurin from Pseudonomas aeruginosa, have been investigated as a function of temperature by protein film voltammetry. To this purpose, both proteins have been physisorbed on a pyrolytic graphite edge electrode. A pronounced negative shift of the plastocyanin standard potential, compared to a slight shift in the case of azurin, has been found upon increasing the temperature. Hence, significant conformational and/or solvation changes accompany the redox conversion of plastocyanin. Lower electron transfer rate constants (by c.a. one order of magnitude) and higher activation enthalpies have been found for plastocyanin as compared to azurin. The voltammetric response of azurin vanishes irreversibly at temperatures close to 60 °C, whereas the redox properties of plastocyanin remain unaltered, except for some loss of electroactive protein, after heating the electrode at temperatures as high as 90 °C.Ministerio de Economía y Competitividad CTQ 2008-00371, BFU2009-07190Junta de Andalucía P07-FQM-02492, P06-CVI-0171

Potentiostatic infrared titration of 11-mercaptoundecanoic acid monolayers

In situ IR difference spectra of 11-mercaptoundecanoic acid monolayers deposited on gold have been recorded as a function of both solution pH* and substrate's potential. IR spectra recorded under voltammetric conditions indicate that the potential-induced ionization of the monolayer is a slow process, involving a simultaneous rearrangement of the hydrocarbon chains, and that a significant population of carboxylic groups are not dissociated at positive potentials in a pH* 9 solution. Steep potentiostatic IR titration curves, consistent with a monolayer pKa = 4.3, are obtained at negative potentials. As the potential is made more positive, titration curves become lower, broader and are shifted towards more basic pHs. Rather than acting directly on the electrostatic energy of the carboxylate groups, the electrode potential seems to control the ionization of the monolayer by attracting (or repelling) cations from the electrolyte and by reorienting the thiol head groups inside and outside the low permittivity layer of methylene chains.Dirección General de Investigación Científica y Técnica CTQ2008-00371Junta de Andalucía P07-FQM-0249

Structural and functional insights into lysine acetylation of cytochrome c using mimetic point mutants

Post-translational modifications frequently modulate protein functions. Lysine acetylation in particular plays a key role in interactions between respiratory cytochrome c and its metabolic partners. To date, in vivo acetylation of lysines at positions 8 and 53 has specifically been identified in mammalian cytochrome c, but little is known about the structural basis of acetylation-induced functional changes. Here, we independently replaced these two residues in recombinant human cytochrome c with glutamine to mimic lysine acetylation and then characterized the structure and function of the resulting K8Q and K53Q mutants. We found that the physicochemical features were mostly unchanged in the two acetyl-mimetic mutants, but their thermal stability was significantly altered. NMR chemical shift perturbations of the backbone amide resonances revealed local structural changes, and the thermodynamics and kinetics of electron transfer in mutants immobilized on gold electrodes showed an increase in both protein dynamics and solvent involvement in the redox process. We also observed that the K8Q (but not the K53Q) mutation slightly increased the binding affinity of cytochrome c to its physiological electron donor, cytochrome c1—which is a component of mitochondrial complex III, or cytochrome bc1—thus suggesting that Lys8 (but not Lys53) is located in the interaction area. Finally, the K8Q and K53Q mutants exhibited reduced efficiency as electron donors to complex IV, or cytochrome c oxidase.Ministerio de Ciencia e Innovación PGC2018-096049-B-I00Junta de Andalucía BIO-198, US-1254317, US-1257019, P18-FR-3487, P18-HO-409

Bond behavior of lightweight concretes containing coated pumice aggregate: hinged beam approach

Emiroglu, Mehmet/0000-0002-0214-4986WOS: 000369433600006This paper presents an experimental study for determining the bond performance of lightweight concretes produced using pumice aggregate coated with colemanite-cement paste. For this purpose, eight hinged beam specimens were produced with four different concrete mixtures. 14 mm deformed bars with 10 Phi development lengths were selected constant for all test specimens. All the specimens were tested in bending and load-slip values were measured experimentally to determine the effect of colemanite-cement coated pumice aggregate on bond performances of lightweight concretes. Test results showed that, colemanite-cement coated pumice aggregate increases compressive strength and bond performance of the lightweight concretes, considerably