• Bulletin of the Korean Chemical Society
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• 제32권7호
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• pp.2423-2427
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• 2011

Pseudo-first-order rate constants ($k_{obsd}$) have been measured spectrophotometrically for nucleophilic substitution reactions of 3,4-dinitrophenyl diphenylphosphinothioate 9 with alkali metal ethoxides (EtOM, M = Li, Na, K) in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. The plot of $k_{obsd}$ vs. [EtOM] is linear for the reaction of 9 with EtOK. However, the plot curves downwardly for those with EtOLi and EtONa while it curves upwardly for the one with EtOK in the presence of 18-crown-6-ether (18C6). Dissection of $k_{obsd}$ into $k_{EtO^-}$ and $k_{EtOM}$ (i.e., the second-order rate constant for the reaction with dissociated $EtO^-$ and ion-paired EtOM, respectively) has revealed that the reactivity increases in the order $k_{EtOLi}$ < $k_{EtONa}$ < $k_{EtO^-}$ ${\approx}$ $k_{EtOK}$ < $k_{EtOK/18C6}$, indicating that the reaction is inhibited by $Li^+$ and $Na^+$ ions but is catalyzed by 18C6-crowned $K^+$ ion. The reactivity order found for the reactions of 9 contrasts to that reported previously for the corresponding reactions of 1, i.e., $k_{EtOLi}$ > $k_{EtONa}$ > $E_{EtOK}$ > $k_{EtO^-}$ ${\approx}$ $k_{EtOK/18C6}$, indicating that the effect of changing the electrophilic center from P=O to P=S on the role of $M^+$ ions is significant. A four-membered cyclic transition-state has been proposed to account for the $M^+$ ion effects found in this study, e.g., the polarizable sulfur atom of the P=S bond in 9 interacts strongly with the soft 18C6-crowned $K^+$ ion while it interacts weakly with the hard $Li^+$ and $Na^+$ ions.

• Journal of Pharmaceutical Investigation
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• 제22권3호
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• pp.173-183
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• 1992

To study the feasibility of transmucosal delivery of $[D-ala^2]-methionine$ enkephalinamide (YAGFM), its enzymatic degradation and stabilization in various rabbit mucosal extracts were investigated by HPLC method. The degradation of YAGFM was observed to follow the first-order kinetics and the half-lives of YAGFM in the nasal, rectal and vaginal mucosal extracts were found to be 25.7, 3.0 and 7.8 hr, respectively. However, there was no significant difference in degradation rates of YAGFM between the mucosal and serosal extracts obtained from the same mucosal membrane. This finding suggests that even a synthetic enkephalin analog, which is designed to be resistent to aminopeptidases, needs to be fully protected from the enzymatic degradation in mucosal sites for the delivery of the analog through mucosal routes. To inhibit the degradation of YAGFM in various mucosal extracts, effects of enzyme inhibitors such as bestatin (BS), amastatin (AM), thiorphan (TP), thimerosal (TM) and EDTA, alone or in combination, and modified cyclodextrins were observed by assaying YAGFM staying intact during 24 hr-incubation at $37^{\circ}C$. It was found from the results that mixed inhibitors such as TM (0.5 mM)/EDTA (5 mM) or AM $(50{\mu}M)/TM$ (0.5 mM)/EDTA (5 mM) provided very useful means for the stabilization in various mucosal extracts. The latter was found to protect YAGFM from the degradation in the nasal, rectal, and vaginal mucosal extracts by 90.9, 90.4 and 91.3%, respectively, after 24 hr-incubation, suggesting almost complete inhibition of YAGFM-degrading enzymes present in the incubation mixture. However, BS $(50{\mu}M)$, AM 50 $(50{\mu}M)$ or TP$(50{\mu}M)$ alone did not reveal sufficient inhibition except TM (0.5 mM) or EDTA (5 mM). The adddition of $2-hydroxylpropyl-{\beta}-cyclodextrin$(10%) to the nasal mucosal extract, and $dimethyl-{\beta}-cyclodextrin$(10%) to the rectal and vaginal mucosal extracts reduced the first-order rate constants for the degradation of YAGFM by 5.8, 17.3 and 8.9 times, respectively, compared to those with no additive.

• Bulletin of the Korean Chemical Society
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• 제25권2호
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• pp.226-232
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• 2004

Ground and low-lying electronic states of Cr atoms in the gas phase were generated from photolysis of $Cr(CO)_6$ vapor in He or Ar using an unfocussed weak UV laser pulse and their reactions with $O_2$ and $N_2O$ were studied. When 0.5-1.0 Torr of $Cr(CO)_6$ /$O_2$ /He or Ar mixtures were photolyzed using 295-300 nm laser pulses, broadband chemiluminescence peaked at ~420 and ~500 nm, respectively, was observed in addition to the atomic emissions from $z^7P^{\circ}$, $z^5P^{\circ}$, and $y^7P^{\circ}$ states of Cr atoms. When $N_2O$ was used instead of $O_2$, no chemiluminescence was observed. The chemiluminescence intensities as well as the LIF intensities for those three low-lying electronic states ($a^7S_3,\;a^5S_2\;and\;a^5D_J$) showed second-order dependence on the photolysis laser power. Also, the chemiluminescence intensities were first-order in $O_2$ pressure, but the presence of excess Ar showed a strong inhibition effect on them. Based on the experimental results, the chemiluminecent species in this work is attributed to $CrO_2^*$ generated from hot ground state Cr atoms with $O_2$. The apparent radiative lifetimes of the chemiluminescent species and collisional quenching rate constants by $O_2$ and Ar also were investigated.

• The Korean Journal of Physiology and Pharmacology
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• 제22권1호
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• pp.71-80
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• 2018

In patients with epilepsy, depression is a common comorbidity but difficult to be treated because many antidepressants cause pro-convulsive effects. Thus, it is important to identify the risk of seizures associated with antidepressants. To determine whether paroxetine, a very potent selective serotonin reuptake inhibitor (SSRI), interacts with ion channels that modulate neuronal excitability, we examined the effects of paroxetine on Kv3.1 potassium channels, which contribute to high-frequency firing of interneurons, using the whole-cell patch-clamp technique. Kv3.1 channels were cloned from rat neurons and expressed in Chinese hamster ovary cells. Paroxetine reversibly reduced the amplitude of Kv3.1 current, with an $IC_{50}$ value of $9.43{\mu}M$ and a Hill coefficient of 1.43, and also accelerated the decay of Kv3.1 current. The paroxetine-induced inhibition of Kv3.1 channels was voltage-dependent even when the channels were fully open. The binding ($k_{+1}$) and unbinding ($k_{-1}$) rate constants for the paroxetine effect were $4.5{\mu}M^{-1}s^{-1}$ and $35.8s^{-1}$, respectively, yielding a calculated $K_D$ value of $7.9{\mu}M$. The analyses of Kv3.1 tail current indicated that paroxetine did not affect ion selectivity and slowed its deactivation time course, resulting in a tail crossover phenomenon. Paroxetine inhibited Kv3.1 channels in a use-dependent manner. Taken together, these results suggest that paroxetine blocks the open state of Kv3.1 channels. Given the role of Kv3.1 in fast spiking of interneurons, our data imply that the blockade of Kv3.1 by paroxetine might elevate epileptic activity of neural networks by interfering with repetitive firing of inhibitory neurons.

• Biomolecules & Therapeutics
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• 제1권1호
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• pp.1-8
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• 1993

It has been known that calcium antagonists also inhibit the radioligand binding to muscarinic and $\alpha$-adrenergic receptors and, in case of verapamil, these inhibitions may play a role in the effects of verapamil on the heart. In this study, the effects of nicardipine, nifedipine, nimodipine, diltiazem and verapamil on the binding of [$^3H$]dihydroalprenolol (DHA) to dog cardiac ${\beta}$-adrenergic receptors were examined. A single uniform [$^3H$]DHA binding site ($K_D/= 5nM\;and\;B_{max}=2600$ fmol/mg protein) was identified in dog cardiac sarcolemma. [$^3H$]DHA binding was not affected by the usual therapeutic concentrations of these calcium antagonists (nanomolar range) but in the "nonspecific"concentration ranges ($28-180{\mu}m$) these drugs inhibited [$^3H$]DHA binding to $\beta$-adrenergic receptors. Nicardipine, nifedipine, nimodipine and diltiazem competed for [$^3H$]DHA binding to ${\beta}$-adrenergic receptors with dissociation constants ($K_i$) of $28{\mu}m,\' 74{\mu}m, 39{\mu}m \;and \;35{\mu}m,$ respectively. Verapamil ($K_i=176.5 {\mu}m$) was less potent inhibitor than other drugs and this inhibition was noncompetitive; the maximal binding capacity ($B_{max}$) $300 {\mu}m$ verapamil without change in the apparent dissociation constant (4K_D$) for DHA. These results indicate that the inhibitory action of calcium antagonists at high concentrations on ${\beta}$-adrenergic receptors is not involved in the therapeutic effects of these drugs by the calcium channel blocking action.

• Journal of Pharmaceutical Investigation
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• 제22권1호
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• pp.11-21
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• 1992

The effects of colchicine on the plasma elimination and biliary excretion of various organic anions in rats were examined. Elimination of indocyanine green (ICG) or rose bengal (RB) from plasma was significantly delayed when rats were treated with colchicine (3 mg/kg body weight) 3 hr prior to the administration of the dye. On the other hand, disappearance of sulfobromophthalein (BSP) or bromophenol blue (BPB) from plasma was not influenced by colchicine. The plasma disappearance and biliary excretion of organic anions were kinetically analyzed based on a compartment model, in which the deep compartment and the unknown disposition are incorporated. The transfer rate constants of ICG or RB, $k_{23}$ (from the liver to the deep compartment) and $k_{3B}$ (from the deep compartment to the bile), were decreased by colchicine, but those of BSP or BPB were not changed. A mechanism for the decrease in the $k_{23}$ and $k_{3B}$ values for ICG and RB might be explained by a inhibition of colchicine to the intracellular cytoskeleton. The hepatocellular distribution of RB or BPB was then determined. BPB mainly distributed to the cytosolic fraction, but RB distributed to each hepatocyte organelle. Taken together. it was suggested that ICG or RB is transported through hepatocytes into bile with the aid of the cytoskeleton, whereas BSP or BPB is handled by hepatocytes in a different way.

• Natural Product Sciences
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• 제21권3호
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• pp.176-184
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• 2015

In our search for natural soluble epoxide hydrolase (sEH) inhibitors from plants, an extract of the dried whole plants of Euphorbia supina Rafin was found to significantly inhibit sEH activity in vitro. Phytochemical investigation of E. supina resulted in isolation of 17 compounds (1 - 17), including triterpenes (1 - 4), phenolic compounds (5 - 8), and flavonoid derivatives (9 - 17). The structures of the isolated compounds were established mainly by extensive analysis of the 1D and 2D NMR, and MS data. All of the isolated compounds were evaluated for their sEH inhibitory activity. Among the isolated phenolic compounds, 8 was identified as a significant inhibitor of sEH, with an IC₅₀ value of 15.4 ± 1.3 μM. Additionally, a kinetic analysis of isolated compounds (2, 5, 8 - 11, 13, and 17) indicated that the inhibitory effects of flavonoid derivatives 10 and 11 were of mixed-type, with inhibitory constants (K_i) ranging from 3.6 ± 0.8 to 21.8 ± 1.0 μM, whereas compounds 2, 5, 8, 9, 13, and 17 were non-competitive inhibitors with inhibition K_i values ranging from 3.3 ± 0.2 to 39.5 ± 0.0 μM.

• 멤브레인
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• 제10권2호
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• pp.83-91
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• 2000

불용성 농축어육단백질(fish protein concentration, FPC)의 기능성을 개선하기 위한 목적으로 한외여과막 반응기 (MWCO 5,000)를 사용하여 효소적 가수분해를 시도하였다. 막반응기에서 불용성인 FPC의 막힌현상(fooling)을 완화시키기 위하여 회분식에서 pepsin으로 1차 가수분해하였으며, 그 가수분해물을 한외여과막 반응기에서 pronase E를 사용하여 2차 가수분해하였다. 회분식에서 FPC의 최적가수분해 조건은 45$^{\circ}C$, pH 2.0, 기질 대 효소비 150 (w/w)였으며, 이때의 가수분해도는 약 89%였다. 회분식에서 반응속도 상수 $K_{m}$ 및 V$_{max}$는 각각 1.25%, 0.89 mg/$m\ell$/min이었으며, 기질농도 1.5% 이상에서 기질저해가 있었다. 한외여과막 반응기는 순환속도 474 $m\ell$/min, 투과압력 15 psi로 작동하였으며, 온도에 따른 투과유속은 증가하였으나 pH에 대해서는 거의 일정하였다. 막반응기에서 기질과 2차 가수분해효소 pronase E의 비 (S/E)는 200 (w/w)이 가장 효율적이었으며, 이때의 가수분해물의 생산량은 효소 mg당 702 mg으로 회분식 51 mg에 비해 13배 이상 높았다. FPC 가수분해물의 분자량은 1차 가수분해물의 경우 2,500~20,000 Da 영역에 분포하였으며, 2차 가수분해물은 700~10,000 Da 이었다.

• Biomolecules & Therapeutics
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• 제3권1호
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• pp.21-27
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• 1995

The only compounds with antagonistic activity via AT$_1$receptor, one of two subtypes of angiotensin II (AII) receptor, have been demonstrated to block the vasoconstriction effects of AII and thereby provide therapeutic potential. This initiated the search for compounds with high specific affinity to AT$_1$receptor and their effective screening methods. The radioligand binding assay for the AII receptor is regarded as the primary method for the evaluation of AT$_1$receptor antagonists for their activity. In this paper, we characterized the liver AT$_1$receptor and describe the efficient method of the radioligand binding assay using rat liver as a source of AT$_1$receptor. Equilibrium binding studies with rat adrenal cortex, adrenal medulla, liver and bovine adrenal showed that the specific bindings of [$^3$H] AII were saturable in all tissues and the Scatchard plots of those data were linear, suggesting a single population of binding sites. Hill slopes were very near to the unity in all tissues. Kinetic studies of [$^3$H) AII binding in rat liver homogenates yielded two association rate constants, 4.10$\times$10$^{7}$ M$^{-1}$ min$^{-1}$ and 4.02$\times$10$^{9}$ M$^{-1}$ min$^{-1}$ , with a single dissociation rate constant, 7.07$\times$10$^{-3}$ min-$^{-1}$ , possibly due to the partial dissociation phenomenon. The rank order of inhibition potencies of [$^3$H] AII binding in rat liver was AII>Sarile>Losartan>PD 123177. Rat liver homogenates revealed to have very high density of homogeneous population of the AT$_1$receptor subtype, as the specifically bound [$^3$H] AII was not inhibited by PD 123177, the nonpeptide antagonist of AT$_2$. The results of this study demonstrated that the liver homogenates from rats could be the best receptor preparation for the AT$_1$receptor binding assay and provide an efficient system for the screening of newly synthesized candidate compounds of AT$_1$receptor antagonist.

• 한국미생물·생명공학회지
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• 제9권4호
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• pp.197-205
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• 1981

Bacillus megaterium의 발효액으로 부터 페니실린 아미다제를 셀라이트에 흡착시켜 분리한 후 이 흡착효소를 아크릴아마이드에 포괄시켜 고정화하였다. 관형식 반응조에서의 이 고정화효소의 안정도는 포괄시키지 않은 흡착효소에 비해 크게 증가하였으며 최적 반응 pH는 8.7, 그리고 최적 안정도는 7.5~8.0이었고 최적온도는 5$0^{\circ}C$ 였다. Km과 6-APA, 페닐초산에 의한 저해상수는 각각 4.55mM, 36.5mM, 그리고 10.5mM이었다. Effectiveness factor값은 0.95로 내부확산 효과는 무시할 수 있었다. pH8.0의 조건에서 관형식 반응조 내에서의 효소역가의 반감기는 4$0^{\circ}C$에서 6.8일 그리고 3$0^{\circ}C$ 에서는 47일로 포괄하지 않은 흡착효소에 비해 안정도가 각각 6.8배와 12배로 증가하였다. 이 고정화 효소에 의한 회분식 및 연녹식반응조에서의 6-APA의 생산성을 논의하였다. 실험결과로 미루어 보아 특히 흡착효소를 고정화효소로 사용하는 경우에 포괄방법을 이용함으로써 효소반응조의 안정도를 크게 증가시킬 수 있음을 시사하였다.