アプリケーションレベルの情報提示によるソーシャルエンジニアリング攻撃の拡散防止手法

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Direct electron transfer-type bioelectrocatalysis of redox enzymes at nanostructured electrodes

Direct electron transfer (DET)-type bioelectrocatalysis, which couples the electrode reactions and catalytic functions of redox enzymes without any redox mediator, is one of the most intriguing subjects that has been studied over the past few decades in the field of bioelectrochemistry. In order to realize the DET-type bioelectrocatalysis and improve the performance, nanostructures of the electrode surface have to be carefully tuned for each enzyme. In addition, enzymes can also be tuned by the protein engineering approach for the DET-type reaction. This review summarizes the recent progresses in this field of the research while considering the importance of nanostructure of electrodes as well as redox enzymes. This review also describes the basic concepts and theoretical aspects of DET-type bioelectrocatalysis, the significance of nanostructures as scaffolds for DET-type reactions, protein engineering approaches for DET-type reactions, and concepts and facts of bidirectional DET-type reactions from a cross-disciplinary viewpoint

Development Perspective of Bioelectrocatalysis-Based Biosensors

Bioelectrocatalysis provides the intrinsic catalytic functions of redox enzymes to nonspecific electrode reactions and is the most important and basic concept for electrochemical biosensors. This review starts by describing fundamental characteristics of bioelectrocatalytic reactions in mediated and direct electron transfer types from a theoretical viewpoint and summarizes amperometric biosensors based on multi-enzymatic cascades and for multianalyte detection. The review also introduces prospective aspects of two new concepts of biosensors: mass-transfer-controlled (pseudo)steady-state amperometry at microelectrodes with enhanced enzymatic activity without calibration curves and potentiometric coulometry at enzyme/mediator-immobilized biosensors for absolute determination

Direct electron transfer-type bioelectrocatalysis by membrane-bound aldehyde dehydrogenase from Gluconobacter oxydans and cyanide effects on its bioelectrocatalytic properties

The bioelectrocatalytic properties of membrane-bound aldehyde dehydrogenase (AlDH) from Gluconobacter oxydans NBRC12528 were evaluated. AlDH exhibited direct electron transfer (DET)-type bioelectrocatalytic activity for acetaldehyde oxidation at several kinds of electrodes. The kinetic and thermodynamic parameters for bioelectrocatalytic acetaldehyde oxidation were estimated based on the partially random orientation model. Moreover, at the multi-walled carbon nanotube-modified electrode, the coordination of CN‾ to AlDH switched the direction of the DET-type bioelectrocatalysis to acetate reduction under acidic conditions. These phenomena were discussed from a thermodynamic viewpoint

Role of a non-ionic surfactant in direct electron transfer-type bioelectrocatalysis by fructose dehydrogenase

A heterotrimeric membrane-bound fructose dehydrogenase (FDH) from Gluconobacter japonicus NBRC3260 contains FAD in subunit I and three heme C moieties in subunit II as the redox centers, and is one of the direct electron transfer (DET)-type redox enzymes. FDH-catalyzed current density of fructose oxidation at hydrophilic mercaptoethanol (MEtOH)-modified Au electrode is much larger than that at hydrophobic mercaptoethane (MEtn)-modified Au electrode. Addition of a non-ionic surfactant Triton® X-100 (1%) completely quenches the catalytic current at the MEtn-modified Au electrode, while only small competitive effect is observed at the MEtOH-modified Au electrode. Quartz crystal microbalance measurements support the adsorption of FDH and Triton® X-100 on both of the modified electrodes. We propose a model to explain the phenomenon as follows. The surfactant forms a monolayer on the hydrophobic MEtn-modified electrode with strong hydrophobic interaction, and FDH adsorbs on the surface of the surfactant monolayer. The monolayer inhibits the electron transfer from FDH to the electrode. On the other hand, the surfactant forms a bilayer on the hydrophilic MEtOH-modified electrode. The interaction between the surfactant bilayer and the hydrophilic electrode is relatively weak so that FDH replaces the surfactant and is embedded in the bilayer to communicate electrochemically with the hydrophilic electrode

Numerical Study on Gas-Liquid-Solid Three-phase Flow Assuming Seepage of CO2 Stored under the Seabed

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 佐藤 徹, 東京大学教授 徳永 朋祥, 東京大学教授 多部田 茂, 東京大学特任教授 尾崎 雅彦, 東京大学講師 平林 紳一郎University of Tokyo(東京大学

Autonomous Decentralized Control of Traffic Signals that can Adapt to Changes in Traffic

A major challenge for traffic signal control is adapting to unpredictable changes in traffic. To address this issue, we propose an autonomous decentralized control scheme for traffic signals that is based on physics. More specifically, “virtual impulses” given by red signals or preceding cars, which are defined in a similar manner as the impulses generally used in physics, are calculated at each traffic signal by using an optimal velocity model, and traffic signals are switched to reduce these virtual impulses. We performed simulations under various traffic conditions, and the results showed that the proposed control scheme works adaptively and resiliently in response to each set of circumstances. Thus, the virtual impulse can be a key physical quantity for designing adaptive traffic systems

Presynaptic monoacylglycerol lipase activity determines basal endocannabinoid tone and terminates retrograde endocannabinoid signaling in the hippocampus

金沢大学大学院医学系研究科機能障害学Endocannabinoids function as retrograde messengers and modulate synaptic transmission through presynaptic cannabinoid CB1 receptors. The magnitude and time course of endocannabinoid signaling are thought to depend on the balance between the production and degradation of endocannabinoids. The major endocannabinoid 2-arachidonoylglycerol (2-AG) is hydrolyzed by monoacylglycerol lipase (MGL), which is shown to be localized at axon terminals. In the present study, we investigated how MGL regulates endocannabinoid signaling and influences synaptic transmission in the hippocampus. We found that MGL inhibitors, methyl arachidonoyl fluorophosphonate and arachidonoyl trifluoromethylketone, caused a gradual suppression of cannabinoid-sensitive IPSCs in cultured hippocampal neurons. This suppression was reversed by blocking CB1 receptors and was attenuated by inhibiting 2-AG synthesis, indicating that MGL scavenges constitutively released 2-AG. We also found that the MGL inhibitors significantly prolonged the suppression of both IPSCs and EPSCs induced by exogenous 2-AG and depolarization-induced suppression of inhibition/excitation, a phenomenon known to be mediated by retrograde endocannabinoid signaling. In contrast, inhibitors of other endocannabinoid hydrolyzing enzymes, fatty acid amide hydrolase and cyclooxygenase-2, had no effect on the 2-AG-induced IPSC suppression. These results strongly suggest that presynaptic MGL not only hydrolyzes 2-AG released from activated postsynaptic neurons but also contributes to degradation of constitutively produced 2-AG and prevention of its accumulation around presynaptic terminals. Thus, the MGL activity determines basal endocannabinoid tone and terminates retrograde endocannabinoid signaling in the hippocampus. Copyright © 2007 Society for Neuroscience

Ca2+-assisted receptor-driven endocannabinoid release: mechanisms that associate presynaptic and postsynaptic activities

金沢大学大学院医学系研究科機能障害学Endogenous cannabinoids (endocannabinoids) serve as retrograde messengers at synapses in various regions of the brain. They are released from postsynaptic neurons and cause transient and long-lasting reduction of neurotransmitter release through activation of presynaptic cannabinoid receptors. Endocannabinoid release is induced either by increased postsynaptic Ca2+ levels or by activation of Gq/11-coupled receptors. When these two stimuli coincide, endocannabinoid release is markedly enhanced, which is attributed to the Ca2+ dependency of phospholipase Cβ (PLCβ). This Ca2+-assisted receptor-driven endocannabinoid release is suggested to participate in various forms of synaptic plasticity, including short-term associative plasticity in the cerebellum and spike-timing-dependent long-term depression in the somatosensory cortex. In these forms of plasticity, PLCβ seems to function as a coincident detector of presynaptic and postsynaptic activities. © 2007 Elsevier Ltd. All rights reserved

Essential Insight of Direct Electron Transfer-Type Bioelectrocatalysis by Membrane-Bound d-Fructose Dehydrogenase with Structural Bioelectrochemistry

電極を基質認識できる酵素の反応メカニズムを解明 --次世代バイオセンシングにつながる基盤技術--. 京都大学プレスリリース. 2023-10-16.Flavin adenine dinucleotide-dependent d-fructose dehydrogenase (FDH) from Gluconobacter japonicus NBRC3260, a membrane-bound heterotrimeric flavohemoprotein capable of direct electron transfer (DET)-type bioelectrocatalysis, was investigated from the perspective of structural biology, bioelectrochemistry, and protein engineering. DET-type reactions offer several benefits in biomimetics (e.g., biofuel cells, bioreactors, and biosensors) owing to their mediator-less configuration. FDH provides an intense DET-type catalytic signal; therefore, extensive research has been conducted on the fundamental principles and applications of biosensors. Structural analysis using cryo-electron microscopy and single-particle analysis has revealed the entire FDH structures with resolutions of 2.5 and 2.7 Å for the reduced and oxidized forms, respectively. The electron transfer (ET) pathway during the catalytic oxidation of d-fructose was investigated by using both thermodynamic and kinetic approaches. Structural analysis has shown the localization of the electrostatic surface charges around heme 2c in subunit II, and experiments using functionalized electrodes with a controlled surface charge support the notion that heme 2c is the electrode-active site. Furthermore, two aromatic amino acid residues (Trp427 and Phe489) were located in a possible long-range ET pathway between heme 2c and the electrode. Two variants (W427A and F489A) were obtained by site-directed mutagenesis, and their effects on DET-type activity were elucidated. The results have shown that Trp427 plays an essential role in accelerating long-range ET and triples the standard rate constant of heterogeneous ET according to bioelectrochemical analysis