• 한국미생물·생명공학회지
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• 제35권1호
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• pp.26-29
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• 2007

Tautomycetin(TMC)은 국내 토양에서 분리된 방선균(Streptomyces sp. CK4412)로부터 생합성 되는 항진균성 2차 대사산물로서, Cyclosporin및 FK506과 같은 기존의 면역억제제보다 작용 메카니즘 및 효능이 훨씬 탁월한 선형의 폴리케타이드계 면역억제 화합물이다. 고체배지의 pH변화와 TMC생산성과의 상관관계를 규명하기 위하여, 방선균 CK4412를 다양한 pH조건에서 배양하면서 항진균 활성 및 TMC생산량을 비교분석 하였다. 고체배지의 pH를 산성조건(pH 4-5)으로 유지하여 방선균 CK4412 균주를 배양할 경우, 중성 pH 조건에서 배양한 경우보다 훨씬 탁월한 항진균 활성 및 TMC생산성이 관찰되었다. 본 연구결과는 대표적인 방선균 S. coelicolor에서 입증된 pH-shock게 의한 2차대사산물의 생산성 증대효과가 대사산물의 특성과 균주가 전혀 다른 TMC 생산균주 CK4412에서도 관찰됨을 입증함으로써, pH조절에 의한 다양한 종류의 방선균 유래 유용 생리활성물질의 생산성 증대 전략을 제시하고 있다.

• Journal of Pharmaceutical Investigation
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• 제24권3호
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• pp.139-144
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• 1994

The effect of some formulation variables on the release rate of famotidine, a $H_2$ receptor antagonist, from cellulose matrices containing hydroxypropylcellulose (HPC) in different ratios and types was investigated. The effects of tablet shape and compression pressure on dissolution rate of famotidine were studied. And the effect of the pH of dissolution media was also studied. Increase in the ratio of polymer to drug decreased the release rate of famotidine. Increase of the polymer viscosity also decreased the release rate. The release rate of famotidine was dependent on the pH of dissolution media. The release rate of drug was not much dependent on the compression pressure but dependent on the tablet shape and/or surface area. Consequently, the release rate of famotidine can be modified by changing the HPC contents, types of polymers with different viscosity grades or using appropriate fillers.

• Bulletin of the Korean Chemical Society
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• 제8권4호
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• pp.280-285
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• 1987

FMN-dependent glycolate oxidase from spinach is inactivated by diethyl pyrocarbonate at pH 7.0. Inactivation of both apo- and holoenzyme by diethyl pyrocarbonate follows pseudo-first-order kinetics and first order with respect to the reagent. A series of difference spectra of inactivated and native enzymes show a single peak at 240 nm, indicating the modification of histidyl residues. No decrease in absorbance at around 280 nm due to formation of O-carbethoxytyrosine is observed. The rate of inactivation is dependent on pH, and the data for pH dependent rates implicate the involvement of a group with a pKa of 6.9. The activity lost by treatment with diethyl pyrocarbonate could be almost fully restored by incubation with 0.75M hydroxylamine. The reactivation by hydroxylamine and the pH dependence of inactivation are also consistent with that the inactivation is due to modification of histidyl residues. Although coenzyme FMN is without protective effect, the substrate glycolate, the product glyoxylate, and two competitive inhibitors, oxalate and oxalacetate, provide marked protection against the inactivation of the holoenzyme. These results suggest that the inactivation of the oxidase by diethyl pyrocarbonate occurs by modification of essential histidyl residue(s) at the active site.

• 대한의생명과학회지
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• 제13권2호
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• pp.75-81
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• 2007

Sodium salicylate (NaSal), a chemopreventive drug, has been shown to induce apoptosis and cell circle arrest depending on its concentrations in a variety of cancer cells. In A549 cells, low concentration of NaSal (5$\sim$10 mM) induces cell cycle arrest, whereas it induces apoptosis at higher concentration of 20 mM. In the present study, we examined the molecular mechanism for NaSal-induced cell cycle arrest. NaSal induced expression of p53, p21 (Wafl/Cipl), and p27 (Kipl) that play important roles in cell cycle arrest. p53 induction was mediated by its phosphorylation at Ser-15 that could be prevented by the PI3K-related kinase (ATM, ATR and DNA-PK) inhibitors including wortmannin, caffeine and LY294002. In addition, NaSal-induction of p2l (Wafl/Cipl) was detected in P53 (+/+) wild type A549 cells but not in p53 (-/-) mutant H1299 cells, indicating p53-dependent p21 (Wafl/Cipl) induction. In contrast, p27 (Kipl) that is a negative regulate. of cell cycle with p21 (Wafl/Cipl) was observed both in A549 cells and H1299 cells. Thus, 5 mM NaSal appeared to cause cell cycle arrest through inducing the cyclin-dependent kinase inhibitor p21 (Wafl/Cipl) via PI3K-related protein kinase-dependent p53 activation as well as by up-regulating p27 (Kipl) independently of p53 in A549 cells.

• 한국자기공명학회논문지
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• 제22권4호
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• pp.144-148
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• 2018

Catalytic enzyme Pyrazinamidase (PncA) from Mycobacterium tuberculosis can hydrolyze substrate pyrazinamide (PZA) to pyrazoic acid (POA) as active form of compound. Using NMR spectroscopy, pH-dependent catalytic properties were monitored including metal binding mode during converting PZA to POA. There seems to be a conformational change through zinc binding in active site from the perturbation of peak intensities in series of 2D HSQC spectra the conformation changes through zinc binding.

• The Korean Journal of Physiology and Pharmacology
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• 제7권3호
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• pp.187-191
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• 2003

$Na^+/H^+$ exchanger (NHE) has a critical role in regulation of intracellular pH (pHi) in the renal proximal tubular cells. It has recently been shown that dopamine inhibits NHE in the renal proximal tubules. Nevertheless, there is a dearth of information on the effects of long-term (chronic) dopamine treatment on NHE activities. This study was performed to elucidate the pHi regulatory mechanisms during the chronic dopamine treatments in renal proximal tubular OK cells. The resting pHi was greatly decreased by chronic dopamine treatments. The initial rate and the amplitude of intracellular acidification by isosmotical $Na^+$ removal from the bath medium in chronically dopamine-treated cells were much smaller than those in control. Although it seemed to be attenuated in $Na^+$-dependent pH regulation system, $Na^+$-dependent pHi recovery by NHE after intracelluar acid loading in the dopamine-treated groups was not significantly different from the control. The result is interpreted to be due to the balance between the stimulation effects of lower pHi on the NHE activity and counterbalance by dopamine. Our data strongly suggested that chronic dopamine treatment increased intrinsic intracellular buffer capacity, since higher buffer capacity was induced by lower resting pHi and this effect could attenuate pHi changes under extracellular $Na^+$-free conditions in chronically dopamine-treated cells. Our study also demonstrated that intracellular acidification induced by chronic dopamine treatments was not mediated by changes in NHE activity.

• Journal of Applied Biological Chemistry
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• 제61권3호
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• pp.213-217
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• 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.

• Journal of Microbiology and Biotechnology
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• 제14권2호
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• pp.243-249
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• 2004

The toxicity of inorganic sulfuric acid as a stressor was characterized in Saccharomyces cerevisiae KNU5377. In this work, we examined physiological responses to low extracellular pH $(pH_{ex})$ caused by inorganic $H_2SO_4$, which could not affect cell growth after pH was adjusted to an optimum with Trizma base. The major toxicity of sulfuric and was found to be reduction of environmental pH, resulting in stimulation of plasma membrane ${H^+}-ATPase$, which in turn contributed to intracellular alkalinization. Using a pH-dependent fluorescence probe, 5-(and-6)-carboxy SNARF-1, acetoxymethyl ester, acetate (carboxy SNARF-1 AM acetate), to determine $pH_{in}$, we found that color was dependent on the changes of intracellular pH which coincided with calculated $pH_{in}$ of alkalinization up to approximately pH 7.3. This alkalinization did not seem to affect survival of these cells exposed to 30 mM sulfuric acid, which lowered the $pH_{ex}$ of the glucose containing growth media up to approximately pH 3.0; however, the cells could grow only up to 70% of the maximum growth in the same media, when 30 mM sulfuric acid was added.

• BMB Reports
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• 제38권4호
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• pp.468-473
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• 2005

The energetics of nitrate uptake by intact cells of the halotolerant cyanobacterium Aphanothece halophytica were investigated. Nitrate uptake was inhibited by various protonophores suggesting the coupling of nitrate uptake to the proton motive force. An artificially-generated pH gradient across the membrane (${\Delta}pH$) caused an increase of nitrate uptake. In contrast, the suppression of ${\Delta}pH$ resulted in a decrease of nitrate uptake. The increase of external pH also resulted in an enhancement of nitrate uptake. The generation of the electrical potential across the membrane ($\Delta\psi$) resulted in no elevation of the rate of nitrate uptake. On the other hand, the valinomycin-mediated dissipation of $\Delta\psi$ caused no depression of the rate of nitrate uptake. Thus, it is unlikely that $\Delta\psi$ participated in the energization of the uptake of nitrate. However, $Na^+$-gradient across the membrane was suggested to play a role in nitrate uptake since monensin which collapses $Na^+$-gradient strongly inhibited nitrate uptake. Exogenously added glucose and lactate stimulated nitrate uptake in the starved cells. N, N'-dicyclohexylcarbodiimide, an inhibitor of ATPase, could also inhibit nitrate uptake suggesting that ATP hydrolysis was required for nitrate uptake. All these results indicate that nitrate uptake in A. halophytica is ATP-dependent, driven by ${\Delta}pH$ and $Na^+$-gradient.

• Bulletin of the Korean Chemical Society
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• 제15권10호
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• pp.896-900
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• 1994

The pH-dependent reduction behavior of N-monosubstituted-4,4'-bipyridinium ions ($RBPY^+: R=methyl(C_1)$; benzyl; n-octyl; n-dodecyl) has been investigated by electrochemical and spectroelectrochemical techniques. At acidic condition, $RBPY^+$ is protonated and the protonated species are reduced by two consecutive one-electron processes. The $2e^-$ reduced species undergoes a chemical reaction with $H^+$. The second-order rate constant $(k_H)$ of the homogeneous chemical process is $(3.7{\pm}0.3){\times}10^3M^{-1}s^{-1}$ for the two electron reduction product of $C_1BPY^+$. At high pH, the electrode reduction of $RBPY^+$ is one-step $2e^-$ transfer process with concomitant addition of $H^+$, which is confirmed by cyclic voltammetric study using a microdisk electrode.