• Journal of Life Science
• /
• 제9권2호
• /
• pp.44-48
• /
• 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
• /
• 제61권3호
• /
• pp.213-217
• /
• 2018

Pseudomonas tolaasii에 의해 분비되는 톨라신은 펩티드 독소로서, 버섯 자실체 구조와 세포를 파괴하여 갈반병을 일으킨다. 톨라신의 독성은 용혈활성을 측정함으로서 평가하며, 이는 톨라신 분자가 적혈구 막에 pore를 형성하여 세포 구조를 파괴하기 때문이다. 이전 연구에서, $Zn^{2+}$ 뿐만 아니라 $Ni^{2+}$이 톨라신의 세포독성에 억제효과를 가짐을 확인하였다. $Ni^{2+}$은 농도가 증가함에 따라 톨라신에 의한 용혈작용을 저해하였으며, 이의 $K_i$ 값은 1.8 mM이었다. 용혈활성은 10 mM 이상의 농도에서 완전히 저해되었다. $Ni^{2+}$의 효과는 pH에 따라 크게 변하지 않았으나, $Zn^{2+}$의 톨라신 세포독성 억제 효과는 염기성 pH에서 크게 증가하였다. 완충액의 pH를 7에서 9로 증가시키면, 50% 용혈작용이 일어나는 시간인 $T_{50}$은 1 mM $Ni^{2+}$에 의해 조금 증가하였으나 $100{\mu}M$ $Zn^{2+}$에서는 크게 증가하였다. $Zn^{2+}$와 $Ni^{2+}$을 반응용액에 동시에 처리하였을 때, 두 양이온의 상승효과는 모든 pH에서 나타났다. 서로 다른 pH 의존성을 보이는 두 금속이온의 분자적 설명은 톨라신의 pore 형성과 세포 독성에 관한 기작의 이해에 기여할 것이다.

• 분석과학
• /
• 제8권4호
• /
• pp.617-622
• /
• 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.

• 한국물환경학회지
• /
• 제18권2호
• /
• pp.169-187
• /
• 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
• /
• 제10권1호
• /
• pp.96-101
• /
• 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.

• 한국식품과학회지
• /
• 제8권4호
• /
• pp.253-259
• /
• 1976

단백질 분해효소로서 넓은 특이성을 가지고 있는 Pronase를 사용하여 두 가지의 다른 방법으로 고정화효소(固定化酵素)를 제조하였다. Sepharose에 직접 결합시킨 효소는 원래 효소활성도의 22.6%을 유지하고 있었지만, Extension arm으로서 $-CH_2-$ 기의 수가 6, 10, 12를 가진 ${\omega}-amino-alkyl\;group$을 사용하여 Sepharose에 결합시킨 효소는 원래 효소활성도의 거의 100%를 다 유지하고 있었다. 제조한 고정화효소(固定化酵素)의 pH효과, 온도효과 및 Km을 조사하였으며 GRAS list에 들지 않은 Pronase를 식품가공에 이용하는 가능성을 고찰하였다.

• 분석과학
• /
• 제13권1호
• /
• pp.41-48
• /
• 2000

돼지의 소장조직을 탄소반죽에 혼입시켜 과산화수소 정량 바이오센서를 제작하고, 기질농도와 pH변화가 전극의 효소반응속도에 미치는 영향을 관찰하였다. 수학적 취급이 용이하도록 매개체는 첨가하지 않았다. 관찰된 현상들을 정량적으로 처리하여 전극반응에 관련된 효소의 전기화학적 특성과 최대 반응속도를 구하였다. 또, pH에 따른 Michaelis 상수의 변화로부터 여러 가지 열역학적 파라미터를 얻고, 이를 이용하여 효소활동의 최적 pH를 구하는 방법을 고안하였다.

• 한국방사성폐기물학회:학술대회논문집
• /
• 한국방사성폐기물학회 2017년도 추계학술논문요약집
• /
• pp.353-354
• /
• 2017

• BMB Reports
• /
• 제29권3호
• /
• pp.210-214
• /
• 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.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1995년도 하계학술대회 논문집 C
• /
• pp.1205-1208
• /
• 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.