• Bulletin of the Korean Chemical Society
• /
• v.32 no.6
• /
• pp.1884-1890
• /
• 2011

A series of Ni(II) and Pd(II) complexes bearing N4-type tetradentate ligands, [Ni($X^1X^2$-6-$Me_2bpb$) 1] and [Pd($X^1X^2$-6-$Me_2bpb$) 2]; 6-$Me_2bpb$ = N,N'-(o-phenylene)bis(6-methylpyridine-2-carboxamidate), $X^1$ = Cl, H, or $CH_3$, $X^2$ = $NO_2$, Cl, F, H, $CH_3$, or $OCH_3$) were designed, synthesized, and characterized to investigate electronic and steric effects of ligand on the norbornene polymerization catalysts. Using modified methylaluminoxanes as an activator, the complexes exhibited high catalytic activities for the polymerization of norbornene and the nickel complexes exhibited better catalytic activity the palladium complexes. Ni complex 1a with $NO_2$ group on the benzene ring showed the highest catalytic activity of $4.9{\times}10^6$ g of PNBEs/$mol_{Ni}{\cdot}h$ and molecular weight of $15.28{\times}10^5$ g/mol with PDI < 2.30. Complexes with electron-withdrawing groups are more thermally stable (> 100 $^{\circ}C$), and tend to afford higher polymerization productivities than the ones having electron-donating groups. Amorphous polynorbornenes were obtained with good solubility in halogenated aromatic solvents. A vinyl addition mechanism has been proposed for the catalytic polymerization.

• Bulletin of the Korean Chemical Society
• /
• v.31 no.7
• /
• pp.1907-1914
• /
• 2010

A novel catalytic kinetic method is proposed for the determination of Se(IV), Se(VI) and total inorganic selenium in water based on the catalytic effect of Se(IV) on the reduction of bromate by p-nitrophenylhydrazine at pH 3.0. The generated bromine, $Br_2$ or $Cl_2$ plus $Br_2$ in 0.1 M NaCl (or NaBr) environment efficiently decolorized Calmagite and the reaction was monitored spectrophotometrically at 523 nm as a function of time. In this indicator reaction, bromide acted as an activator for the catalysis of selenium (IV) and a reducing agent for selenium (VI) at pH 3.0, which allowed the determination of total selenium. The fixed time method was adopted for the determination and speciation of inorganic selenium. Under the optimum conditions, the calibration graph are linear in the range 1 - 35 ${\mu}gL^{-1}$ of Se(IV) for the fixed time method at $25^{\circ}C$. The detection limit based on statistical $3S_{blank}$/m-criterion was 0.215 ${\mu}gL^{-1}$ for the fixed time method (7 min). All of the variables that affect the sensitivity at 523 nm were investigated, and the optimum conditions were established. The interference effect of various cations and anions on the Se (IV) determination was also studied. The selectivity of the selenium determination was greatly improved with the use of the strongly cation exchange resin such as Amberlite IR120 plus. The proposed kinetic method was validated statistically and through recovery studies in natural water samples. The RSDs for ten replicate measurements of 5, 15 and 25 ${\mu}gL^{-1}$ of Se(IV) and Se(VI) was changed between 2.1 - 4.85%. Analyses of a certified standard reference material (NIST SRM 1643e) for selenium using the fixed-time method showed that the proposed kinetic method has good accuracy. Se(IV), Se(VI) and total inorganic selenium in environmental water samples have been successfully determined by this method after selective reduction of Se(VI) to Se(IV).

• Bulletin of the Korean Chemical Society
• /
• v.10 no.6
• /
• pp.595-599
• /
• 1989

The effects of phosphatidic acid(PA) on the activity of phospholipase D were examined in detail. The enzyme activity was examined in the liposome system containing phosphatidylcholine and PA, which was suspended in a desired buffer solution by ultrasonication. The substrate of large unilamella vesicle (LUV) state by ultrasonication was more effective on the enzyme activity than that of multilamella vesicle(MLV) by water-bath type sonication. The most effective molar ratio of PC-PA liposome for enzyme activity was found to be 1:0.7. The other optimum conditions were found 5 mM $Ca^{2+}$ ion, pH 6.6, and incubation temperature of $27^{\circ}C. K_m \;and \;V_{max}$ values were estimated to be 1.43 mM and 0.8 $nmole/min/{\mu}g$ protein respectively. These properties in a PC-PA liposome system were compared with those in a PC-SDS mixed micelle system. The effects of other phospholipids and organic phosphates on the enzyme activity were also examined.

• Journal of Life Science
• /
• v.32 no.11
• /
• pp.882-889
• /
• 2022

Breast cancer anti-estrogen resistance 3 (BCAR3) has been identified as one of the genes that induces anti-estrogen resistance in breast cancer. We have previously reported that BCAR3 activates promoters of c-Jun, activator protein-1, and the serum response element. In this study, we investigated the functional role of BCAR3 in the activation of the estrogen response element (ERE) in normal human breast MCF-12A cells. Transient expression of BCAR3 induced ERE activation, which was further increased by 17β-estradiol treatment but was not blocked by the anti-estrogen tamoxifen. Next, we studied the signaling pathway of BCAR3 leading to ERE activation. BCAR3-mediated ERE activation was inhibited by LY294002 and AZD5363, inhibitors of the phosphatidylinositol (PI) 3-kinase pathway, but not by PD98059 and U0126, inhibitors of the mitogen-activated protein kinase pathway. ERE activation was induced by the catalytic subunit p110α. of PI3-kinase or the active mutant of Akt, and this activation was not further increased by additional BCAR3 transfection. Based on these results, we propose that BCAR3 plays an important role in ERE activation through the PI3-kinase/Akt pathway in human breast MCF-12A cells.

• BMB Reports
• /
• v.32 no.1
• /
• pp.60-66
• /
• 1999

Matrix metalloproteinase-2 (MMP-2; 72-kDa gelatinase; 72-kDa type IV collagenase; gelatinase A) plays an important role in normal physiological processes and in many pathologic processes such as arthritis and metastasis of cancer. Tissue inhibitor of metalloproteinases-2 (TIMP-2) binds to proMMP-2 or mature MMP-2 at a 1:1 ratio and inhibits the catalytic activity of MMP-2. We demonstrated that the baculovirus/insect cell system does not have TIMP-2 activity. The human proMMP-2 free of TIMP-2 was expressed in the expression system and purified by one-step affinity chromatography using gelatin-Sepharose. The free proMMP-2 was autoactivated to the mature MMP-2 and autodegraded into smaller molecular weight forms in the absence of external activator. The activation and autodegradation of the proMMP-2 was much more rapid in the presence of 4-aminophenylmercuric acetate (APMA). Addition of TIMP-2 inhibits both APMA-induced activation and autodegradation of the free proMMP-2. However, an increasing concentration of TIMP-2 more readily inhibited activation of the free proMMP-2 than autodegradation. These results demonstrate that TIMP-2 plays roles in inhibition of both activation and autodegradation of the free proMMP-2 in addition to inhibition of the catalytic activity of MMP-2.

• Bulletin of the Korean Chemical Society
• /
• v.32 no.5
• /
• pp.1500-1506
• /
• 2011

Tyrosinase is a widespread enzyme with great promising capabilities. The Lineweaver-Burk plots of the catecholase reactions showed that the kinetics of mushroom tyrosinase (MT), activated by $Co^{2+}$ and $Zn^{2+}$ at different pHs (6, 7, 8 and 9) obeyed the non-essential activation mode. The binding of metal ions to the enzyme increases the maximum velocity of the enzyme due to an increase in the enzyme catalytic constant ($k_{cat}$). From the kinetic analysis, dissociation constants of the activator from the enzyme-metal ion complex ($K_a$) were obtained as $5{\times}10^4M^{-1}$ and $8.33{\times}10^3M^{-1}$ for $Co^{2+}$ and $Zn^{2+}$ at pH 9 and 6 respectively. The structural analysis of MT through circular dichroism (CD) and intensive fluorescence spectra revealed that the conformational stability of the enzyme in these pHs reaches its maximum value in the presence of each of the two metal ions.

• BMB Reports
• /
• v.31 no.3
• /
• pp.227-232
• /
• 1998

The leukocyte NADPH oxidase of neutrophils is a membrane-bound enzyme that catalyzes the production of $O_2^-$ from oxygen using NADPH as an electron donor. Dormant in resting neutrophils, the enzyme acquires catalytic activity when the cells are exposed to appropriate stimuli. During activation, the cytosolic oxidase components $p47^{phox}$ and $p67^{phox}$ migrate to the plasma membrane, where they associate with cytochrome $b_{558}$, a membrane-bound flavohemoprotein, to assemble the active oxidase. The oxidase can be activated in a cell-free system; the activating agent usually employed is an anionic amphiphile such as sodium dodecyl sulfate (SDS). Because $p47^{phox}$ can translocate by itself during activation, the conformational change in $p47^{phox}$ may be responsible for the activation of NADPH oxidase. We show here that the treatment of $p47^{phox}$ with SDS leads to an increase in the reactivity of the sutbydryl group of cysteines toward N-ethylmaleimide, indicating that the conformational change occurs when $p47^{phox}$ is exposed to SDS. We propose that this change in conformation results in the appearance of a binding site through which $p47^{phox}$ interacts with cytochrome $b_{558}$during the activation process.

• Journal of Microbiology and Biotechnology
• /
• v.26 no.5
• /
• pp.967-974
• /
• 2016

Zearalenone (ZEA) is an estrogenic mycotoxin that is produced by several Fusarium species, including Fusarium graminearum. One of the ZEA biosynthetic genes, ZEB2, encodes two isoforms of Zeb2 by alternative transcription, forming an activator (Zeb2L-Zeb2L homooligomer) and an inhibitor (Zeb2L-Zeb2S heterodimer) that directly regulate the ZEA biosynthetic genes in F. graminearum. Cyclic AMP-dependent protein kinase A (PKA) signaling regulates secondary metabolic processes in several filamentous fungi. In this study, we investigated the effects of the PKA signaling pathway on ZEA biosynthesis. Through functional analyses of PKA catalytic and regulatory subunits (CPKs and PKR), we found that the PKA pathway negatively regulates ZEA production. Genetic and biochemical evidence further demonstrated that the PKA pathway specifically represses ZEB2L transcription and also takes part in posttranscriptional regulation of ZEB2L during ZEA production. Our findings reveal the intriguing mechanism that the PKA pathway regulates secondary metabolite production by reprograming alternative transcription.

• BMB Reports
• /
• v.46 no.12
• /
• pp.567-574
• /
• 2013

Liver plays a major role in maintaining glucose homeostasis in mammals. Under fasting conditions, hepatic glucose production is critical as a source of fuel to maintain the basic functions in other tissues, including skeletal muscle, red blood cells, and the brain. Fasting hormones glucagon and cortisol play major roles during the process, in part by activating the transcription of key enzyme genes in the gluconeogenesis such as phosphoenol pyruvate carboxykinase (PEPCK) and glucose 6 phosphatase catalytic subunit (G6Pase). Conversely, gluconeogenic transcription is repressed by pancreatic insulin under feeding conditions, which effectively inhibits transcriptional activator complexes by either promoting post-translational modifications or activating transcriptional inhibitors in the liver, resulting in the reduction of hepatic glucose output. The transcriptional regulatory machineries have been highlighted as targets for type 2 diabetes drugs to control glycemia, so understanding of the complex regulatory mechanisms for transcription circuits for hepatic gluconeogenesis is critical in the potential development of therapeutic tools for the treatment of this disease. In this review, the current understanding regarding the roles of two key transcriptional activators, CREB and FoxO1, in the regulation of hepatic gluconeogenic program is discussed.

• Molecules and Cells
• /
• v.26 no.3
• /
• pp.258-264
• /
• 2008

A rice diacylglycerol kinase (DGK) gene, OsBIDK1, which encodes a 499-amino acid protein, was cloned and characterized. OsBIDK1 contains a conserved DGK domain, consisting of a diacylglycerol kinase catalytic subdomain and a diacylglycerol kinase accessory subdomain. Expression of OsBIDK1 in rice seedlings was induced by treatment with benzothiadiazole (BTH), a chemical activator of the plant defense response, and by infection with Magnaporthe grisea, causal agent of blast disease. In BTH-treated rice seedlings, expression of OsBIDK1 was induced earlier and at a higher level than in water-treated control seedlings after inoculation with M. grisea. Transgenic tobacco plants that constitutively express the OsBIDK1 gene were generated and disease resistance assays showed that overexpression of OsBIDK1 in transgenic tobacco plants resulted in enhanced resistance against infection by tobacco mosaic virus and Phytophthora parasitica var. nicotianae. These results suggest that OsBIDK1 may play a role in disease resistance responses.