• Journal of Life Science
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• v.9 no.2
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• pp.44-48
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• 1999

The ionization of tyrosine residue is known to be involved in the stabilization of transition-state in catalysis of astacin based upon the astacin-transition state analog structure. Two tyrosine residues, Tyr-216 and Tyr-219, are conserved in all MMPs related with astacin family, We replaced Tyr-216 and Tyr-219 into phenylalanine, respectively and the zinc binding properties, kinetic parameters, and pH dependence of each mutant are determined in order to examine the role of tyrosine residue in matrilysin catalysis. Both mutants contain two zinc atoms per mol of enzyme, indicating that either tyrosime does not affect the zinc binding property of the enzyme. Y216F and Y219F mutants are highly active and the kcat/Km values are only decreased 1.1-1.5-fold compared to the wild-type enzyme. The decrease in the activity of the mutants is essentially due to the increase in Km value. The pH dependencies of the kcat/Km values for both mutants are similar to the corresponding dependencies obtained with the wild type enzyme. The pKa values at the alkaline side of both mutants are not changed. These kinetic and pH dependence results indicate that the ionization of active site tyrosine residue of matrilysin is not reflected in the kinetics of peptide hydrolysin as catalyzed by astacin.

• Journal of Applied Biological Chemistry
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• v.61 no.3
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• pp.213-217
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• 2018

Tolaasin secreted by Pseudomonas tolaasii is a peptide toxin and causes brown blotch disease on the cultivated mushrooms by collapsing cellular and fruiting body structure. Toxicity of tolaasin was evaluated by measuring hemolytic activity because tolaasin molecules form membrane pores on the red blood cells and destroy cell membrane structure. In the previous studies, we found that tolaasin cytotoxicity was suppressed by $Zn^{2+}$ and $Ni^{2+}$. $Ni^{2+}$ inhibited the tolaasin-induced hemolysis in a dose-dependent manner and its $K_i$ value was 1.8 mM. The hemolytic activity was completely inhibited at the concentration higher than 10 mM. The inhibitory effect of $Zn^{2+}$ on tolaasin-induced hemolysis was increased in alkaline pH, while that of $Ni^{2+}$was not much dependent on pH. When the pH of buffer solution was increased from pH 7 to pH 9, the time for 50% hemolysis ($T_{50}$) was increased greatly by $100{\mu}M$ $Zn^{2+}$; however, it was slightly increased by 1 mM $Ni^{2+}$ at all pH values. When the synergistic effect of $Zn^{2+}$ and $Ni^{2+}$ on tolaasin-induced hemolysis was measured, it was not dependent on the pH of buffer solution. Molecular elucidation of the difference in pH-dependence of these two metal ions may contribute to understand the mechanism of tolaasin pore formation and cytotoxicity.

• Analytical Science and Technology
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• v.8 no.4
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• pp.617-622
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• 1995

Electrocatalytic reduction of dioxygen has been investigated by cyclic voltammetry at glassy carbon electrode modified with new Co(II)-Schiff base complexes in aqueous solutions of various pH. The reduction potentials of dioxygen at chemically adsorbed electrodes show the dependence of pH between pH 4 and 14. The catalytic effect is large and the reaction occurs via two or four electron transfer in various pH solution.

• Journal of Korean Society on Water Environment
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• v.18 no.2
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• pp.169-187
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• 2002

The effects of important parameters such as reaction time and pH on the Fenton's process were evaluated using a batch reactor. It was proven that organic materials and heavy metals in leachate could be successfully removed by Fenton's reagent. Favorable operation conditions were investigated. It was observed that the reaction between ferrous iron and hydrogen peroxide with the production of hydroxyl radical was almost complete in 10 minutes. That is, the oxidation of organic materials by Fenton's reagent was so fast that it was complete in 30 minutes with batch experiments. With the formation of carbonic acid, pH of the batch reactor decreased to favorable acidic conditions without acid addition. The oxidation of organic materials in the leachate showed a pH dependence and was most efficient in the pH range of 2-3.

• Bulletin of the Korean Chemical Society
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• v.10 no.1
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• pp.96-101
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• 1989

The infrared multiphoton decomposition of trichloroethylene-H(TCE-H) and trichloroehtylene-D(TCE-D) was studied by using the high power $CO_2$ laser. The pressure dependence of TCE-H decomposition showed that the HCl elimination channel to form ClC ≡ CCl was the major step at high pressures, while the HC ≡ CCl formation step became important at low pressures. $Cl_2C$ = CHCl ${\rightarrow}$ (high pressure) ClC ${\equiv}$ CCl + HCl ${\rightarrow}$ (low pressure) HC ${\equiv}$ CCl + 2Cl${\cdot}$($Cl_2$) The IRMPD of TCE-H and TCE-D mixtures with 10P(20) laser line showed that optimum conditions of large isotope selectivity were the low system pressures and high laser powers. The experimentally observed dependence of the branching ratios on the pressure and laser fluence, and the isotope selectivity coefficients were quantitatively explained by using the modified energy grained master equations (EGME) model.

• Korean Journal of Food Science and Technology
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• v.8 no.4
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• pp.253-259
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• 1976

Two kinds of sepharose-bound pronases were successfully prepared. The immobilized pronase, directly coupled to cyanogen-bromide activated sepharose, retains 22.6% of original specific activity against casein. However, ${\omega}-aminoalkyl$ sepharose immobilized pronases, in which extension arms of ${\omega}-aminoalkyl$ group $(number\;of\;-CH_2-\;is\;8,\;10,\;and\;12)$ are used, retain almost 100% of original specific activity. Studies of enzyme stability, pH dependence, temperature dependence, and Km values are presented.

• Analytical Science and Technology
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• v.13 no.1
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• pp.41-48
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• 2000

A biosensor for the determination of hydrogen peroxide was constructed by immobilizing of porcine small instestinal tissue in a plain carbon paste, and the effect of varying the $H_2O_2$ concentration and pH on the rate of catalytic reaction was evaluated. For the mathematical simplicity, no mediator was added. Electrochemical properties and the maximal rate could be derived from the quantitative analysis of the observed phenomena related to the electrode reaction. Also, pH dependence of the Michaelis constant enabled to calculate various thermodynamic parameters and subsequently to design a electrochemical method to determine the optimum pH of enzyme.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2017.10a
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• pp.353-354
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• 2017

• BMB Reports
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• v.29 no.3
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• pp.210-214
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• 1996

The pH dependence of the kinetic parameters of mutant O-acetylserine sulfhydrylase (OASS) from Salmonella typhimurium LT-2 has been determined in order to obtain information on the chemical mechanism. The initial velocity pattern obtained by varying the concentrations of OAS at several fixed concentrations of TNB, shows an intersection on the left of the ordinate at pH 7.0, indicating that the kinetic mechanism is a sequential mechanism in which substrate inhibition by OAS is observed while the wild type enzyme showed a ping pong mechanism. The values of $V/E_t$, $V/K_{OAS}E_{t}$ and $V/K_{TNB}E_{t}$ decreased by about 68%, 14% and 16% as compared with the wild type enzyme. The $V/K_{OAS}E_{t}$ is a pK of 6.5 on the acid side of the pH profile, and the $V/K_{TNB}$ is pH independent. As compared with the wild type enzyme, the pKs in the V/K profiles are shifted, reflecting that binding of the cofactor in free E:OAS is less asymmetric.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1205-1208
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• 1995

The optically-gated p-i-n diode switches have been fabricated with gold-compensated silicon. The turn-on and turn-off delay times and the rise and fall times were measured as a function of optical power level, bias, and pulse width. The turn-on characteristics shows a strong dependence an optical pulse power and a delay time(${\delta}{\iota}$) between two pulses, but a weak dependence on the width of optical pulse. Actually there is no turn-off delay in gold-doped p-i-n switches and the fall time is negligible.