• Journal of Microbiology and Biotechnology
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• v.21 no.2
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• pp.154-161
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• 2011

L. lactis sk071115 has been shown to grow more actively and generate lower levels of lactate in glucose-defined medium with nitrate than in medium with Mn(IV). By adding Mn(IV) to a L. lactis culture, lactate production was relatively reduced in combination with Mn(II) production, but cell mass production levels did not increase. Both cell-free extract and intact L. lactis cells reacted electrochemically with Mn(IV) but did not react with Mn(II) upon cyclic voltammetry using neutral red (NR) as an electron mediator. A modified graphite felt cathode with NR (NR-cathode) was employed to induce electrochemical reducing equivalence for bacterial metabolism. Cell-free L. lactis extract catalyzed the reduction of Mn(IV) to Mn(II) under both control and electrochemical reduction conditions; however, the levels of Mn(II) generated under electrochemical reduction conditions were approximately 4 times those generated under control conditions. The levels of Mn(II) generated by the catalysis of L. lactis immobilized in the NR-cathode (L-NR-cathode) under electrochemical reduction conditions were more than 4 times that generated under control conditions. Mn(II) production levels were increased by approximately 2.5 and 4.5 times by the addition of citrate to the reactant under control and electrochemical reduction conditions, respectively. The cumulative Mn(II) produced from manganese ore by catalysis of the L-NR-cathode for 30 days reached levels of approximately 3,800 and 16,000 mg/l under control and electrochemical reduction conditions, respectively. In conclusion, the electrochemical reduction reaction generated by the NR-cathode activated the biochemical reduction of Mn(IV) to Mn(II) by L. lactis.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.6
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• pp.529-536
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• 2008

Cyanobacteria Synechocystis PCC 6803 or the extracted thylakoid membrane from this strain was appled to photosynthetic bio-electrochemical fuel cell(PBEFC) for the production of hydrogen under the illumination of 48Klux using halogen lamp. PBEFC was composed of anode, cathode and membrane between them. Electrode material was carbon paper while electron mediator and receptor were added phenazine methosulfate(PMS) and potassium ferricyanide respectively. When water and 50 mM tricine buffer and $300{\mu}M$ PMS were added to the anode under the light condition, PBEFC produced the current density $4.4{\times}10^{-5}\;mA/cm^2$, $1.4{\times}10^{-4}\;mA/cm^2$ and $2.4{\times}10^{-4}\;mA/cm^2$, respectively. And the addition of the thylakoid membrane to the system increased current density to $1.3{\times}10^{-3}\;mA/cm^2$. Two times increase of the thylakoid membrane into the anode doubled the current density to $2.6{\times}10^{-3}\;mA/cm^2$. But the current density was not increased proportionally to the amount of thylakoid membrane increased. The system was unstable to measure the electricity output due to the foam production in the anode. Addition of triton X-100 and tween 80 stabilized the system to measure the electricity output but the current density was not increased higher than $8.4{\times}10^{-4}\;mA/cm^2$ and $2.3{\times}10^{-3}\;mA/cm^2$. When the thylakoid membrane was substituted to Synechocystis PCC 6803 cells of four-day culture which has chlorophyll contents $20.5{\mu}g/m{\ell}$, maximum current density was $1.3{\times}10^{-3}\;mA/cm^2$ with $1\;k{\Omega}$ resistance.

• Applied Chemistry for Engineering
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• v.3 no.1
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• pp.138-147
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• 1992

Chemically-modified electrodes were fabricated and their electrocatalytic behaviors have been investigated. As a modifying layer, poly-[1-methyl-3-(pyrrol-1-ylmethyl) pyridinium] was electropolymerized onto Pt electrodes under constant current. The thickness of the polymer film was controlled by means of total charge consumed during the electropolymerization. SEM was used to measure the thickness. There was a linear relationship between the passed charge and the film thickness. Ferro/ferricyanide, used as an electron mediator in this study, was rapidly ion-exchanged into the polymer layer with its concentration of 1.2~1.3M. It was found that electrooxidation of ascorbic acid is catalyzed by incorporated ferri/ferrocyanide couple. Kinetic parameters for electrooxidation were determined by RDE experiments. The results indicate that the present system corresponds to ER+S case based on the Saveant theory. Improving methods have been proposed to be R+S case which is ideal for electrocatalysis.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.38 no.5 s.118
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• pp.1-8
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• 2006

This study was performed to evaluate extensive electrochemical characteristics of 23 commercially available mediators for laccase. Electrochemical properties, interactions with laccases, and ability to degrade lignin were compared for selected mediators. Among them, NNDS has very similar electrochemical properties in terms of reversibility and redox potential (about 470 mV vs. Ag/AgCl at pH=7) compared to ABTS which is a well-known mediator. Specific activity of purified laccase from Cerrena unicolor was determined by both 2,2'-azino-bis-(3-ethylbenz-thiazoline-6-sulfonic acid) (ABTS) and 1-nitroso-2-naphthol -3,6-disulfonic acid (NNDS). The specific activity of the laccase was 23.2 units/mg with ABTS and 21.2 units/mg with NNDS. The electron exchange rate for NNDS with laccase was very similar to that for ABTS, which meant that NNDS had similar mediating capability to ABTS. Determining methanol concentration after reacting with laccase compared to lignin degradation capabilities of both ARTS and NNDS. ARTS or NNDS alone cannot degrade lignin, but in the presence of laccase enhanced the rate of lignin degradation. ABTS showed better activity in the beginning, and the reaction rate of NNDS with lignin was about a half of that of ABTS at 10 minute, but the final concentration of methanol produced in 1 hour was very similar each other. The reason for similar methanol concentration for both ABTS and NNDS can be interpreted as the initial activity of ABTS was better than that of NNDS, but ABTS would be inhibited laccase activity more during the incubation.

• Analytical Science and Technology
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• v.12 no.3
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• pp.218-223
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• 1999

A single use, screen-printed sensor for the measurement of liquid phase ethanol was developed and its electrochemical performance was investigated. Disposable type edthanol sensor was fabricated by serially screen printing the carbon paste, silverd pasted and insulator inlon a polyester substrate to pattern working and reference electrode sites and electrical contact. Alcohol dehydrogenase(ADH) or alcohol oxidase(AOD) together with appropriate electron transfer mediators was immobilized on the working electrode. To improve the sensitivity and reproducibility of carbon paste electrode, some pretreatment procedures were applied and their resultant electrochemical performance was examined. The disposable type electrochemical ethanol sensor developed in this study conveniently determines the ethanol in liquid samples such as blood and in fermentation process.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1153-1159
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• 2013

A novel solid-contact indium(III)-selective sensor based on bis-(1H-benzimidazole-5-methoxy-2-[(4-methoxy-3, 5-dimethyl-1-pyridinyl) 2-methyl]) thiosulfinate, known as an omeprazole dimer (OD) and a neutral ionophore, was constructed, and its performance characteristics were evaluated. The sensor was prepared by applying a membrane cocktail containing the ionophore to a graphite rod pre-coated with polyethylene dioxythiophene (PEDOT) conducting polymer as the ion-to-electron transducer. The membrane contained 3.6% OD, 2.3% oleic acid (OA) and 62% dioctyl phthalate (DOP) as the solvent mediator in PVC and produced a good potentiometric response to indium(III) ions with a Nernstian slope of 19.09 mV/decade. The constructed sensor possessed a linear concentration range from $3{\times}10^{-7}$ to $1{\times}10^{-2}$ M and a lower detection limit (LDL) of $1{\times}10^{-7}$ M indium(III) over a pH range of 4.0-7.0. It also displayed a fast response time and good selectivity for indium(III) over several other ions. The sensor can be used for longer than three months without any considerable divergence in potential. The sensor was utilized for direct and flow injection potentiometric (FIP) determination of indium(III) in alloys. The parameters that control the flow injection method were optimized. Indium(III) was quantitatively recovered, and the results agreed with those obtained using atomic absorption spectrophotometry, as confirmed by the f and t values. The sensor was also utilized as an indicator electrode for the potentiometric titration of fluoride in the presence of chloride, bromide, iodide and thiocyanate ions using indium(III) nitrate as the titrant.

• The Korean Journal of Pharmacology
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• v.21 no.1
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• pp.12-26
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• 1985

The generation of $O^{-}_{2}{\cdot}$ and its toxic effects were studied with rat brain mitochondria. The production of $O^{-}_{2}{\cdot}$ from mitochondria in the presence of succinate and antimycin was demonstrated by SOD-inhibitable reduction of NBT. Although succinate can support the $O^{-}_{2}{\cdot}$ formation, the highest rate needs antimycin indicating that blockade of electron flow in the respiratory chain augments the univalent reduction of molecular oxygen. Under this condition, $H_2O_2$ was also observed to be produced. But its formation appears to be derived from the dismutation of the primary product, $O^{-}_{2}{\cdot}$ since the rate of $H_2O_2$ production was markedly decreased by NBT and ferricytochrome c. The $O^{-}_{2}{\cdot}$ and $H_2O_2$ produced were able to cause toxic actions to mitochondrial and extra-mitochondrial components as shown by lipid peroxidation of mitochondrial membrane, and inactivation and lysis of isocitrate dehydrogenase and erythrocytes added to the medium, respectively. In all the toxic actions observed, $Fe^{++}$ was required. It appears that in the toxic actions $OH{\cdot}$ generated from the iron-catalyzed Haber-Weiss reaction acts as a mediator. This was supported by the finding that mitochondria in the presence of succinate and antimycin produced ethylene from methional, and $Fe^{++}$ added increased the ethylene production. The observed toxic actions of mitochondrial $O^{-}_{2}{\cdot}$ may provide evidence supporting a potential role of mitochondria as a source of oxygen radicals to cause tissue damage.

• The Korean Journal of Physiology and Pharmacology
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• v.3 no.4
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• pp.405-414
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• 1999

The role of platelet-activating factor (PAF) was investigated in intestinal ischemia/reperfusion (I/R) induced acute lung injury associated with oxidative stress. To induce acute lung injury following intestinal I/R, superior mesenteric arteries were clamped with bulldog clamp for 60 min prior to the 120 min reperfusion in Sprague-Dawley rats. Acute lung injury by intestinal I/R was confirmed by the measurement of lung leak index and protein content in bronchoalveolar lavage (BAL) fluid. Lung leak and protein content in BAL fluid were increased after intestinal I/R, but decreased by WEB 2086, the PAF receptor antagonist. Furthermore, the pulmonary accumulation of neutrophils was evaluated by the measurement of lung myeloperoxidase (MPO) activity and the number of neutrophils in the BAL fluid. Lung MPO activity and the number of neutrophils were increased (p＜0.001) by intestinal I/R and decreased by WEB 2086 significantly. To confirm the oxidative stress induced by neutrophilic respiratory burst, gamma glutamyl transferase (GGT) activity was measured. Lung GGT activity was significantly elevated after intestinal I/R (p<0.001) but decreased to the control level by WEB 2086. On the basis of these experimental results, phospholipase $A_2\;(PLA_2),$ lysoPAF acetyltransferase activity and PAF contents were measured to verify whether PAF is the causative humoral factor to cause neutrophilic chemotaxis and oxidative stress in the lung following intestinal I/R. Intestinal I/R greatly elevated $PLA_2$ activity in the lung as well as intestine (p<0.001), whereas WEB 2086 decreased $PLA_2$ activity significantly (p<0.001) in both organs. LysoPAF acetyltransferase activity, the PAF remodelling enzyme, in the lung and intestine was increased significantly (p<0.05) also by intestinal I/R. Accordingly, the productions of PAF in the lung and intestine were increased (p<0.001) after intestinal I/R compared with sham rats. The level of PAF in plasma was also increased (p<0.05) following intestinal I/R. In cytochemical electron microscopy, the generation of hydrogen peroxide was increased after intestinal I/R in the lung and intestine, but decreased by treatment of WEB 2086 in the lung as well as intestine. Collectively, these experimental results indicate that PAF is the humoral mediator to cause acute inflammatory lung injury induced by intestinal I/R.

• Journal of the Korean Electrochemical Society
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• v.2 no.1
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• pp.31-37
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• 1999

Copper-containig enzyme, laccase (Rhus vernicifera) was immobilized onto gold electrode using self-assembly technique and its surface properties and catalytic activities were examined. Laccase is an oxidoreductase capable to oxidize diphenols or diamines by 4-electron reduction of molecular oxygen without superoxide or peroxide intermediates. The electrode surface were modified by $\beta-mercaptopropionate$ to have a net negative charge in neutral solution and positively charged laccase (pI=9) was immobilized by electrostatic interaction. The successful immobilization was confirmed by cyclic voltammograms which showed typical surface-confined shapes and behaviors. The amount of charge to reduce the surface was similar to the charge calculated assuming the surface being covered by monolayer. The activity of the immobilized enzyme was tested by the capbility of oxidizing a substrate, ABTS (2,2-azine-bis-(3-ethylbenzthioline-6-sulfonic acid) and it was maintained for $2\~3$ days at $4^{\circ}C$. The immobilzed laccase showed about $10\~15\%$ activity compared to that in solution. The laccase-modified electrode showed the activity of elefoocatalytic reduction of oxygen in the presence of mediator, $Fe(CN)_6^{3-}$ The addtion of azide which is an inhibitor of laccase compeletly eliminated the catalytic current.

• Journal of the Korean Wood Science and Technology
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• v.38 no.3
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• pp.262-273
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• 2010

In the enzymatic hydrolysis of rice straw and wood meals using extra-cellular enzymes from Fomitopsis palustris, key factors which enhanced the sugar conversion yield were investigated in this work, such as enzyme production and enzyme reaction conditions, surfactant effects, and the surface structure of substrates. F. palustris cultured with softwood mixture produced 12.0 U/$m{\ell}$ for endo-${\beta}$-1,4-gulcanase (EG), 116.68 U/$m{\ell}$ for ${\beta}$-glucosidase (BGL), 18.82 U/$m{\ell}$ for cellobiohydrolase (CBH), and 13.33 U/$m{\ell}$ for ${\beta}$-xylosidase (BXL). These levels of BGL, CBH, and BXL activities were two to four folds more than enzyme activities of F. palustris cultured with rice straw. The optimum reaction conditions of cellulase-RS which produced by F. palustris with rice straw and cellulase-SW which produced by F. palustris with softwood mixture were pH 5.0 at $45^{\circ}C$ and pH 5.0 at $50^{\circ}C$, respectively. The sugar conversion yield of cellulase-SW had the highest value of $40.6{\pm}0.6%$ within 72 h when rice straw was used as substrate. By adding 0.1% Tween 20 (w/w-substrate), the sugar conversion yield of rice straw was increased to 44%, which was about four fifths sugar conversion yield of commercial enzyme, Celluclast 1.5L (Novozyme A/S). A low crystallinity and an intensive fibril surface observed by the scanning electron microscope may explain the high sugar conversion yield of rice straw.