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When an enzymatic reaction is extremely fast, the mediated bioelectrocatalytic reaction on the microelectrodes produces a pseudo-steady-state current that is independent of the enzyme ...activity. To understand this phenomenon, I derive the semi-analytical formula for this system. The semi-analytical formula reproduces the results calculated by the numerical simulations. Based on the analytical formula, the current responses of this system can be fully understood. Furthermore, the analytical formula clearly reveals the conditions necessary to expand the linear range of the current with respect to the substrate concentration; small diffusion coefficient of the substrate, small Michaelis constant for the substrate, large diffusion coefficient of the mediator, large radius of the microelectrode, and high enzyme activity. The results obtained here could be useful for the development of a biosensor using microelectrodes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Recently, a smaller-ion shell (SiS) model was developed to describe the electrostatic interaction between ions in solutions (D. Fraenkel, Mol. Phys., 108, 1435 (2010)). The analytical formula based ...on the SiS model reproduces experimental data very well with only one fitting parameter (namely, ion size parameter, a). However, a numerical simulation of the SiS model does not agree with the analytical formula. This indicates that the analytical formula does not represent the SiS model correctly. Therefore, the ion size parameter (a) obtained by fitting Fraenkel’s analytical formula to the experimental data is physically meaningless.
Direct electron transfer (DET)-type bioelectrocatalytic waves of bilirubin oxidase (BOD)-catalyzed O2 reduction and NiFe hydrogenase (H2ase)-catalyzed H2 oxidation are very small and un-detectable ...using glassy carbon (GC) electrodes, respectively; however, clear catalytic waves are observed when the enzymes are adsorbed on Ketjen black-modified GC (KB-GC) electrodes, in which KB provides mesopores for DET-type bioelectocatalysis. To explain the phenomena, we focus on the curvature effect of mesoporous structures on long range electron transfer kinetics and simulate steady-state voltammograms catalyzed by model redox enzymes adsorbed with a random orientation on planar and mesoporous electrodes based on a three-dimensional model. In the simulation, we assume a spherical enzyme with a radius of r, an active site located at a certain distance from the center of the enzyme, and a spherical pore with a radius of Rp in mesoporous electrodes in which the enzyme is trapped and adsorbed. The simulation reveals that mesoporous electrodes provide platforms suitable for DET-type bioelectrocatalysis of enzymes when Rp becomes close to r. Such curvature effects of mesoporous electrodes become especially notable for larger sized enzymes. Furthermore, the simulation reproduces the experimental data of BOD- and H2ase-catalyzed DET-type waves by considering the crystal structures of the enzymes. This work will open a route to improve the kinetic performance of the DET-type bioelectrocatalysis that has become very important in its practical application to a variety of bioelectrochemical devices.
To investigate the effect of mesoporous media as electrodes for the observation of a noncatalytic Faradaic current of redox proteins adsorbed on an electrode (i.e., redox peaks in adsorption ...voltammetry), we propose a simulation model with randomly oriented redox proteins to obtain adsorption voltammograms. Furthermore, we compare the simulated currents of redox proteins adsorbed on planar and mesoporous electrodes. In this model, a redox protein is postulated as a sphere with the active site located at a certain distance from the center of the protein. For a mesoporous electrode, a spherical pore with a radius of R p is assumed. When R p is close to the radius of the protein, a redox peak is obtained even when the active site is located at a great distance from the protein surface; however, the peak is not observed for a planar electrode. This is ascribed to an increase in the number of proteins with orientations suitable for electron transfer because of the curvature effect of the pore. This work indicates that mesoporous media with appropriate pore sizes will provide suitable platforms for several redox proteins to produce observable Faradaic currents.
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IJS, KILJ, NUK, PNG, UL, UM
Electrostatic interactions greatly affect the interaction and activity of ions and charged molecules. In this study, electrochemical techniques were applied to evaluate the electrostatic interactions ...of zwitterions and proteins as charged molecules that have partially overlapped electric field. The formal potential of a probe redox couple, Fe(CN)63−/4−, was used as a measure of the electrostatic interaction between the probe ions and linear amino acids as zwitterions. The zwitterions clearly showed electrostatic interaction with Fe(CN)63−/4−, but the strength was weakened by the partial overlapping of the electric field of oppositely charged sites. Furthermore, we investigated the electrostatic interaction between proteins as multivalent polymeric ions using quinohemoprotein amine dehydrogenase and its electron accepter proteins (amicyanin, cytochrome c550, and horse heart cytochrome c). The second-order reaction rate constant (k) of the intermolecular electron transfer between the proteins was electrochemically determined in various ionic strengths (I). The I dependences of k were explained not by the net charges but by the local charges around the interaction interfaces of the proteins.
Patients with chronic granulomatous disease (CGD) who have mutated phagocyte NADPH oxidase are susceptible to infections due to reduced reactive oxygen species production and exhibit autoimmune and ...inflammatory diseases in the absence of evident infection. Neutrophils and macrophages have been extensively studied since phagocyte NADPH oxidase is mainly found only in them, while the impact of its deficiency on lymphocyte cellularity is less well characterized. We showed herein a zymosan-induced systemic inflammation model that CGD mice deficient in the phagocyte NADPH oxidase gp91phox subunit (NOX2) exhibited more severe thymic atrophy associated with peripheral blood and splenic lymphopenia and reduced lymphopoiesis in the bone marrow in comparison with the wild-type mice. Conversely, the zymosan-exposed CGD mice suffered from more remarkable neutrophilic lung inflammation, circulating and splenic neutrophilia, and enhanced granulopoiesis compared with those in zymosan-exposed wild-type mice. Overall, this study provided evidence that NOX2 deficiency exhibits severe thymic atrophy and lymphopenia concomitant with enhanced neutrophilic inflammation in a zymosan-induced systemic inflammation model.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Effects of the electrode poential on the activity of an adsorbed enzyme has been examined by using copper efflux oxidase (CueO) as a model enzyme and by monitoring direct electron transfer (DET)-type ...bioelectrocatalysis of oxygen reduction. CueO adsorbed on bare Au electrodes at around the point of zero charge (Epzc) shows the highest DET activity, and the activity decreases as the adsorption potential (Ead; at which the enzyme adsorbs) is far from Epzc. We propose a model to explain the phenomena in which the electrostatic interaction between the enzyme and electrodes in the electric double layer affects the orientation and the stability of the adsorbed enzyme. The self-assembled monolayer of butanethiol on Au electrodes decreases the electric field in the outside of the inner Helmholtz plane and drastically diminishes the Ead dependence of the DET activity of CueO. When CueO is adsorbed on bare Au electrodes under open circuit potential and then is held at hold potentials (Eho) more positive than Epzc, the DET activity of the CueO rapidly decreases with the hold time. The strong electric field with positive surface charge density on the metallic electrode (σM) leads to fatal denaturation of the adsorbed CueO. Such denaturation effect is not so serious at Eho<<Epzc, but the electric field with negative σM induces an orientation inconvenient for the DET reaction during the adsorption process. A positively charged neomycin shows a promoter ability to CueO adsorbed at Ead<<Epzc. The phenomenon is also explained on the proposed model.
•The state of CueO on the electrode is monitored amperometrically.•CueO shows the highest activity at around the pzc of Au electrode.•The SAM on Au electrodes diminishes the potential dependence of the DET activity.•The DET activity of CueO held at positive potential decreases with the time.•The electrostatic interaction between CueO and electrodes affects the orientation and the stability of the adsorbed enzyme.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•The state of FDH on the Au electrode is voltammetrically monitored with DET catalytic current, O2 reduction current, and Fe(CN)63−/4− redox signal.•FDH shows the highest activity at around the pzc ...of Au electrode.•The DET activity of FDH decreases with time at positive electrode potentials due to the strong positive electric field.•Mercaptoethanol-Au binding located in the gap of the adsorbed FDH plays a significant role in the stability of the adsorbed FDH on the Au electrode.
Effects of the electrode potential on a direct electron transfer (DET)-type bioelectrocatalysis of fructose dehydrogenase (FDH) at Au electrodes were investigated. Adsorbed FDH showed the highest DET activity at an adsorption potential (Ead) around the point of zero charge (Epzc). Since FDH stock solution contains 2-mercaptoethanol (ME) for stabilization, ME is partially bound to the Au electrode. However, the DET activity drastically decreased at Ead>>Epzc. Au oxide layer is formed at the positive potentials to hinder the interfacial electron transfer. In contrast, only slight decrease in the DET activity was observed at sufficiently negative Ead (<<Epzc), where ME is reductively desorbed from the Au electrode, but co-exists in the solution. In contrast, when FDH and ME were adsorbed on Au electrodes at an open circuit potential and the FDH- and ME-adsorbed Au electrode was held at such a negative hold potential (Eho) in the buffer without ME, the DET activity drastically decreased. An addition of ME in the test solution prevented the decrease in the DET activity at the negative Eho. These results indicate that ME close to adsorbed FDH plays a significant role in the stabilization of FDH adsorbed on Au electrodes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Reverse electrodialysis (RED) power generation using seawater (SW) and river water is expected to be a promising environmentally friendly power generation system. Experiments with large RED stacks ...are needed for the practical application of RED power generation, but only a few experimental results exist because of the need for large facilities and a large area of ion-exchange membranes (IEMs). In this study, to predict the power output of a large RED stack, the power generation performances of a lab-scale RED stack (40 membrane pairs and 7040 cm2 total effective membrane area) with several IEMs were evaluated. The results were converted to the power output of a pilot-scale RED stack (299 membrane pairs and 179.4 m2 total effective membrane area) via the reference IEMs. The use of low-area-resistance IEMs resulted in lower internal resistance and higher power density. The power density was 2.3 times higher than that of the reference IEMs when natural SW was used. The net power output was expected to be approximately 230 W with a pilot-scale RED stack using low-area-resistance IEMs and natural SW. This value is one of the indicators of the output of a large RED stack and is a target to be exceeded with further improvements in the RED system.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Standard NiFe-hydrogenase from Desulfovibrio vulgaris Miyazaki F (DvMF-H2ase) catalyzes the uptake and production of hydrogen (H2) and is a promising biocatalyst for future energy devices. However, ...DvMF-H2ase experiences oxidative inactivation under oxidative stress to generate Ni-A and Ni-B states. It takes a long time to reactivate the Ni-A state by chemical reduction, whereas the Ni-B state is quickly reactivated under reducing conditions. Oxidative inhibition limits the application of DvMF-H2ase in practical devices. In this research, we constructed a mediated-electron-transfer system by co-immobilizing DvMF-H2ase and a viologen redox polymer (VP) on electrodes. The system can avoid oxidative inactivation into the Ni-B state at high electrode potentials and rapidly reactivate the Ni-A state by electrochemical reduction of VP. H2 oxidation and H+ reduction were realized by adjusting the pH from a thermodynamic viewpoint. Using carbon felt as a working-electrode material, high current densities—up to (200 ± 70) and −(100 ± 9) mA cm−3 for the H2-oxidation and H+-reduction reactions, respectively—were attained.
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•DvMF-H2ase- and viologen polymer-co-immobilized MET system was constructed.•Reactivation of Ni-A was realized in a short time in the MET system.•Electrochemical oxidative-inactivation was protected in the MET system.•Bidirectional H2 oxidation and H+ reduction were realized by adjusting pH.•High catalytic-current-densities were achieved by use of carbon felt.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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