• Korean Chemical Engineering Research
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• v.50 no.4
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• pp.723-728
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• 2012

The production of biodiesel by transesterification of soybean oil was performed on $MoO_3$, $SnO_2$ and $CeO_2$ mixed oxides. The catalysts were characterized using XRD and $NH_3$-TPD. $MoO_3$ showed the highest activity among the three metal oxides. When 7 wt% of catalysts was introduced into the reactants, the highest activity was obtained and the water added to reactant decreased the catalytic activity. $MoO_3$ and $SnO_2$ mixed with 50:50 showed the highest activity and $CeO_2$ added with 20% on the $MoO_3-SnO_2$ mixed oxide also showed the highest activity. The catalytic activity showed to have a good relationship with the amount of acid site of catalysts. When the waste soybean oil was used as a reactant, the conversion was decreased about 30%.

• Korean Chemical Engineering Research
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• v.51 no.2
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• pp.163-170
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• 2013

Selective catalytic reduction of $NO_x$ by $NH_3$ ($NH_3$-SCR) over $V_2O_5/TiO_2$-based catalysts is recently reported to be an anthropogenic emitter of $N_2O$ that is a global warming gas with a global warming potential of 310. Therefore, this review will get a touch on significance of some parameters regarding $N_2O$ formation in the $deNO_xing$ reaction for fossil fuels-fired power plants applications. The $N_2O$ production in $NH_3$-SCR reaction with such catalysts occurs via side reactions between $NO_x$ and $NH_3$ in addition to $NH_3$ oxidation, and the extent of these undesired reactions depends strongly on the loadings of $V_2O_5$ as a primary active component and the promoter as a secondary one ($WO_3$ and $MoO_3$) in the SCR catalysts, the feed and operating variables such as reaction temperature, $NO_2/NO_x$ ratio, oxygen concentration, gas hourly space velocity, water content and thermal excursion, and the physical and chemical histories of the catalysts on site. Although all these parameters are associated with the $N_2O$ formation in $deNO_xing$ reaction, details of some of them have been discussed and a better way of suppressing the $N_2O$ production in commercial SCR plants has been proposed.

• Journal of Life Science
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• v.26 no.3
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• pp.353-358
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• 2016

Thiolase is an enzyme that catalyzes condensation reactions between two acetyl-CoA molecules to produce acetoacetyl-CoA. As thiolase catalyzes is the first reaction in the production of n-butanol, knowledge of the molecular and regulatory mechanism of the enzyme is crucial for synthesizing high-value biofuel. Thiolase from Clostridium butyricum (CbTHL) was expressed, purified, and crystallized. X-ray diffraction data were collected from the crystals, and the 3-dimentional structure of the enzyme was determined at 2.0 Å. The overall structure of thiolase was similar to that of type II biosynthetic thiolases, such as thiolase from C. acetobutylicum (CaTHL). The superposition of this structure with that of CaTHL complexed with CoA revealed the residues that comprise the catalytic and substrate binding sites of CbTHL. The catalytic site of CbTHL contains three conserved residues, Cys88, His349, and Cys379, which may function as a covalent nucleophile, general base, and second nucleophile, respectively. For substrate binding, the way in which CbTHL stabilized the ADP moiety of CoA was unlike that of other thiolases, whereas the stabilization of β-mercaptoethyamine and pantothenic acid moieties of CoA was quite similar to that of other enzymes. The most interesting observation in the CbTHL structure was that the enzyme was regulated through redox-switch modulation, using a reversible disulfide bond.

• The Korean Journal of Pharmacology
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• v.30 no.1
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• pp.117-124
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• 1994

Phospholamban is the regulator of $Ca^{2+}-ATPase$ in cardiac sarcoplasmic reticulum(SR). The mechanism of regulation appears to involve inhibition by dephosphorylated phospholamban. Phosphorylation of phospholamban relieves this inhibition. Recently, there has been a report that the cytoplasmic domain (amino acids 1-25) of phospholamban is insufficient to inhibit the $Ca^{2+}$ pump. To explore the domains of phospholamban responsible for $Ca^{2+}-ATPase$ inhibitory activity, we examined the effect of a synthetic phospholamban peptide consisting of amino acid residues 1-25 on $Ca^{2+}$ uptake by reconstituted skeletal SR $Ca^{2+}-ATPase$. The $Ca^{2+}-ATPase$ of skeletal SR was purified and reconstituted in proteoliposomes containing phosphatidylcholine (PC) or phosphatidylcholine: phosphatidylserine (PC:PS). Inclusion of a phospholamban peptide in PC proteoliposomes was associated with significant inhibition of the initial rates of $Ca^{2+}$ uptake at pCa 6.0, and phosphorylation of this peptide by the catalytic subunit of cAMP-dependent protein kinase reversed the inhibitory effect on the $Ca^{2+}$ pump. Similar effects of phospholamban peptide were also observed using PC:PS proteoliposomes. Based on these results, we could conclude that the cytoplasmic domain of phospholamban, containing the phosphorylation sites, by itself is sufficient to inhibit the $Ca^{2+}$ pump of SR.

• Microbiology and Biotechnology Letters
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• v.31 no.2
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• pp.140-144
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• 2003

Type Ⅰ signal peptidase is an integral membrane protein that functions to cleave signal peptides from secreted and membrane proteins. The enzyme serves as a potential target for the development of novel antibacterial agents due to its unique physiological properties. Despite being one of the best characterized enzymes, the catalysis of Type Ⅰ signal peptidase still remains controversy over the catalytic serine/lysine dyad mechanism. It appears that the dyad proteases are generally less efficient than the prototypical serine/histidine/aspartic acid triad found in most enzymes, although Type Ⅰ signal peptidase is an exception to this rule. In this paper, we have proposed that Type Ⅰ signal peptidase may act as the serine/lysine/aspartic acid triad cataltytic mechanism. Therefore, the aspartic acid 99 residue in the E. coli signal peptidase was chosen and mutated to an alanine to see if there is any possible role of the aspartic acid in the catalytic function. Type Ⅰ signal peptidase D99A protein was inactive in vitro assay using the procoat synthesized by in vitro transcription translation. However, the mutant was active using a highly sensitive in vivo assay. Pulse-chase experiments show that the replacement of aspartic acid 99 with alanine results in a very unstable signal peptidase molecule. Therefore, we conclude that it is unlikely that the residue is directly involved in catalysis, but rather plays an important role in stabilizing the protein structure.

• Molecules and Cells
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• v.38 no.5
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• pp.409-415
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• 2015

Low-barrier hydrogen bonds (LBHBs) have been proposed to have important influences on the enormous reaction rate increases achieved by many enzymes. ${\Delta}^5$-3-ketosteroi isomerase (KSI) catalyzes the allylic isomerization of ${\Delta}^5$-3-ketosteroid to its conjugated ${\Delta}^4$-isomers at a rate that approache the diffusion limit. Tyr14, a catalytic residue of KSI, has been hypothesized to form an LBHB with the oxyanion of a dienolate steroid intermediate generated during the catalysis. The unusual chemical shift of a proton at 16.8 ppm in the nuclear magnetic resonance spectrum has been attributed to an LBHB between Tyr14 $O{\eta}$ and C3-O of equilenin an intermediate analogue, in the active site of D38N KSI. This shift in the spectrum was not observed in Y30F/Y55F/D38N and Y30F/Y55F/Y115F/D38N mutant KSIs when each mutant was complexed with equilenin, suggesting that Tyr14 could not form LBHB with the intermediate analogue in these mutant KSIs. The crystal structure of Y30F/Y55F/Y115F/D38N-equilenin complex revealed that the distance between Tyr14 $O{\eta}$ and C3-O of the bound steroi was within a direct hydrogen bond. The conversion of LBHB to an ordinary hydrogen bond in the mutant KSI reduced the binding affinity for the steroid inhibitors by a factor of 8.1-11. In addition, the absence of LBHB reduced the catalytic activity by only a factor of 1.7-2. These results suggest that the amount of stabilization energy of the reaction intermediate provided by LBHB is small compared with that provided by an ordinary hydrogen bond in KSI.

• Korean Chemical Engineering Research
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• v.51 no.4
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• pp.443-454
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• 2013

Various metal ions (transition and base metals) incorporated MCM-41 catalysts can be synthesized using colloidal and soluble silica with non-sodium involved process. Transition metal ion-typically $V^{5+}$, $Co^{2+}$, and $Ni^{2+}$-incorporated MCM-41 catalysts were synthesized by isomorphous substitution of Si ions in the framework. Each incorporated metal ion created a single species in the silica framework, single-site solid catalyst, showing a substantial stability in reduction and catalytic activity. Radius of pore curvature effect was investigated with Co-MCM-41 by temperature programmed reduction (TPR). The size of metallic Co clusters, sub-nanometer, could be controlled by a proper reduction treatment of Co-MCM-41 having different pore size and the initial pH adjustment of the Co-MCM-41 synthesis solution. These small metallic clusters showed a high stability under a harsh reaction condition without serious migration, resulting from a direct anchoring of small metallic clusters to the partially or unreduced metal ions on the surface. After a complete reduction, partial occlusion of the metallic cluster surface by amorphous silica stabilized the particles against aggregations. As a probe reaction of particle size sensitivity, carbon single wall nanotubes (SWNT) were synthesized using Co-MCM-41. A metallic cluster stability test was performed by CO methanation using Co- and Ni-MCM-41. Methanol and methane partial oxidations were carried out with V-MCM-41, and the radius of pore curvature effect on the catalytic activity was investigated.

• Applied Biological Chemistry
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• v.41 no.7
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• pp.489-495
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• 1998

The optimum culture condition of Scopulariopsis brevicaulis for the production of ${\alpha}$-galactosidase was as follows: Tryptone 1.5%, $NH_4NO_3$ 0.2%, Raffinose 2.5%, $KH_2PO_4$ 0.5%, yeast extract 0.5%, pH 7.0, $27^{\circ}C$. The optimum pH and temperature for the enzyme activity of ${\alpha}$-galactosidase producing Scopulariopsis brevicaulis were pH 7.0 and $27^{\circ}C$, respectively. The enzyme was relatively stable at $pH\;6.0{\sim}8.0$ and at temperature below $40^{\circ}C$. The activity of the enzyme was inhibited by $Ag^{2+},\;Hg^{2+},\;Cu^{2+}$, p-chloromercuribenzoic acid and Iodine. These results would indicate the presence of -SH groups in the catalytic site of the enzyme. Km value was 1.9 mM for $p-nitrophenyl-{\alpha}-D-galactopyranoside$ and Vmax value was $9.66{\times}10^2\;{\mu}M/min$. Sugar constituents of culture broth were identified by HPLC that the enzyme liberated sucrose, glucose and fructose from raffinose and raffinose was significantly decreased.

• Applied Chemistry for Engineering
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• v.32 no.1
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• pp.20-27
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• 2021

Effects of the etching treatment of SAPO-34 catalyst were investigated to improve the catalytic lifetime in DTO reaction. The aqueous NH3 solution was a more appropriate treatment agent which could control the degree of etching progress, compared to that of using a strong acid (HCl) or alkali (NaOH) solution. Therefore, the effect on characteristics and lifetime of SAPO-34 catalyst was observed using the treatment concentration and time of aqueous NH3 solution as variables. As the treatment concentration or time of aqueous NH3 solution increased, the growth of erosion was proceeded from the center of SAPO-34 crystal plane, and the acid site concentration and strength gradually decreased. Meanwhile, it was found that external surface area and mesopore volume of SAPO-34 catalyst increased at appropriate treatment conditions. When the treatment concentration and time were 0.05 M and 3 h, respectively, the lifetime of the treated SAPO-34 catalyst was the longest, and was significantly enhanced by ca. 36% (based on DME conversion of > 90%) compared to that of using the untreated catalyst. The model for the etching progress of SAPO-34 catalyst in a mild treatment process using aqueous NH3 solution was also proposed.

• Archives of Pharmacal Research
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• v.25 no.6
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• pp.879-884
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• 2002

Previous study showed that an amidrazonophenylalanine derivative, LB30057, which has high water solubility, inhibited the catalytic activity of thrombin potently by interaction with the active site of thrombin. In the current investigation, we examined whether LB30057 inhibited platelet aggregation and vascular relaxation induced by thrombin. Treatment with LB30057 to plateletrich plasma (PRP) isolated from human blood resulted in a concentration-dependent inhibition of thrombin-induced aggregation. Values for $IC_{50}$ and $IC_{100}$ were $54{\pm}4$ nM and $96{\pm}3$ nM, respectively. This inhibition was agonist (thrombin) specific, since $IC_{50}$ values for collagen and ADP were \much greater than those for thrombin. In addition, concentration-dependent inhibitory effects were observed on the serotonin secretion induced by thrombin in PRP. Consistent with these findings, thrombin-induced increase in cytosolic calcium levels was inhibited in a concentration-dependent manner. When LB30057 was treated with aortic rings isolated from rats, LB30057 resulted in a concentration-dependent inhibition of thrombin-induced vascular relaxation. All these results suggest that LB30057 is a potent inhibitor of platelet aggregation and blood vessel relaxation induced by thrombin.