• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.12
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• pp.6196-6202
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• 2012

Oligo-alginate derivatives were extracted from brown algae and its antimicroalgal effects and reaction mechanism were investigated. Oligo-alginate derivatives were produced from sequential hydrolysis of high molecular weight alginate by treatment of 2 N HCl and 1% $H_2O_2$. Antimicroalgal activity of extracts was proportional to reaction time and activity was highest at 4 hrs. When oligo-alginate derivatives were treated to Akashiwo sanguinea and Cochlodinium polykrikoides, mobilities of cells were ceased. A. sanguinea cells were crushed and plasmolysis was induced in C. polykrikoides cells. To investigate the action mechanism of oligo-alginate derivatives, changes of intracellular (pHi) and extracellular pH (pHe) were determined in the microalgal cells exposed to 0.05% of oligo-alginate derivatives. pHi was decreased about 0.3 unit and pHe was increased about 0.9 unit. These results suggested that change of membrane potential by oligo-alginate derivatives could led to microalgal cell death.

• Journal of the Korean Chemical Society
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• v.54 no.2
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• pp.208-214
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• 2010

In the presence of alcohol, phospholipase D (PLD) is known to perform transphosphatidylation activity, during which the overall reaction rate of PLD increased. To elucidate the reaction mechanism of transphosphatidylation further, we investigated rate constants of transphosphatidylation reaction of the purified ${\alpha}$-type PLD from cabbage in the presence of various alcohols. The second-oder rate constants of PLD transphosphatidylation showed a large increase with the primary alcohols examined as expected. In the case of butanol we observed the second-oder rate constant of $33.33{\pm}1.33M^{-1}sec^{-1}$. This second-order rate constant of transphosphatidylation was as 400 times greater as the second-order hydrolysis rate constant of $0.078M^{-1}sec^{-1}$ which was adjusted for the water concentration. A linear free energy relationship between the $pK_a$ of alcohol and transphosphatidylation rate gives a Br${\o}$nsted slope of ${\beta}_{nu}$ = 0.12 ${\pm}$ 0.03. This small ${\beta}_{nu}$ value implicates that the transition state of break down of phosphatidyl-enzyme intermediate (E-P) is likely dissociative. Finally, a reaction mechanism of cabbage PLD is suggested on the basis of our results presented here and the histidine residue known to be located in the active site of cabbage PLD.

• Journal of Life Science
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• v.30 no.9
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• pp.826-833
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• 2020

Phospholipase C gamma (PLCγ) has critical roles in receptor tyrosine kinase- and non-receptor tyrosine kinase-mediated cellular signaling relating to the hydrolysis of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂] to produce inositol 1,4,5 trisphosphate (IP₃) and diacylglycerol (DAG), which promote protein kinase C (PKC) and Ca²⁺ signaling to their downstream cellular targets. PLCγ has two isozymes called PLCγ1 and PLCγ2, which control cell growth and differentiation. In addition to catalytically active X- and Y-domains, both isotypes contain two Src homology 2 (SH2) domains and an SH3 domain for protein-protein interaction when the cells are activated by ligand stimulation. PLCγ also contains two pleckstrin homology (PH) domains for membrane-associated phosphoinositide binding and protein-protein interactions. While PLCγ1 is widely expressed and appears to regulate intracellular signaling in many tissues, PLCγ2 expression is restricted to cells of hematopoietic systems and seems to play a role in the regulation of immune response. A distinct mechanism for PLCγ activation is linked to an increase in phosphorylation of specific tyrosine residue, Y783. Recent studies have demonstrated that PLCγ mutations are closely related to cancer, immune disease, and brain disorders. Our review focused on the physiological roles of PLCγ by means of its structure and enzyme activity and the pathological functions of PLCγ via mutational analysis obtained from various human diseases and PLCγ knockout mice.

• Journal of Environmental Science International
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• v.17 no.2
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• pp.211-224
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• 2008

Characteristics of the esterification reaction between free fatty acid in rice bran oil and methanol was investigated in the presence of catalysts, such as PTS(p-toluene sulfonic acid), Amberlyst 15 dry and SCX(silica gel based strong cation exchange resin). While reaction temperature was kept constant at $65^{\circ}C$, initial feed content of free fatty acid was varied from 100% to 1% by addition of pure free fatty acid which was previously made from rice bran oil. Also, the effect of mole ratio of methanol to fatty acid on the final conversion was examined. When esterification of pure free fatty acid was catalyzed by several acids, final conversions were increased in order of Amberlyst 15 dry, SCX and PTS. Using PTS catalyst, initially the reaction proceeded in homogeneous 2nd oder reaction mechanism. However, phase of reaction mixture changed from homogeneous to heterogeneous along the reaction time and then reaction rate was retarded by mass transfer resistance of methanol. Final conversion of free fatty acid in reaction mixture was depended on initial feed content of free fatty acid, and had maximum value at 30% of initial feed free fatty acid content for all kinds of catalysts used. And the final conversion was increased with mole ratio of methanol by the improvement of reaction rate. When initial feed free fatty acid content below 10% and the reaction was catalyzed by PTS, concentration of free fatty acid in reaction mixture was increased in the middle of reaction time by hydrolysis of triglyceride in reaction mixture. Also, if silica gel was added into the reaction mixture which had initial feed free fatty acid content below 50%, final conversion was increased by the adsorption of moisture produced. The SCX catalyst made the esterification reaction of free fatty acid to progress like in case of PTS catalyst. However, when initial feed free fatty acid content below 10%, concentration of free fatty acid in. reaction mixture was decreased monotonically and not increased in the middle of reaction time on the contrary to the case of PTS. Thus, SCX catalyst accomplished more high value of final conversion than PTS catalyst for the initial feed fatty acid content range from 50% to 5% In case of initial feed free fatty acid content of 1% and mole ratio of methanol was 2, concentration of free fatty acid in reaction mixture increased over the initial feed free fatty acid content for all kind of catalysts used. Although SCX catalyst was added into reaction mixture which had 1% of initial feed fatty acid content, final conversion was hardly raised by mole ratio of methanol.

• Journal of the Korean Wood Science and Technology
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• v.34 no.3
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• pp.56-63
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• 2006

In order to evaluate the mechanism of cellulose hydrolysis, the complementary DNA encoding Glycoside Hydrolase Family (GHF)74 was cloned from Phanerochaete chrysosporium. Depending on the presence of Cellulose Binding Module (CBM), it can be classified as GHF74A or GHF74B. The GHF74A gene from P. chrysosporium (PcGHF74A) consists of 2163 bp encoding a protein of 721 amino acid residues. The PcGHF74A showed homology of 70~77% compared with the GHF74 from other filamentous fungi. The PcGHF74B, which contains CBM and is a member of family 1, was transcribed to various transcripts depending on the nature of carbon sources and their concentration. To study the possible presence of splice variants in GHF74B transcripts in P. chrysospoium, we carried out RT-PCR analysis using primers that designed based on the annotation data and sequenced data. Our result indicated that PcGHF74B was transcribed to several splicing variants in various culture conditions. Especially in the culture of 2% cellulose, three transcript products were observed. First transcript was presumed to be a full length ORF that contained 11th intron with stop codon at position 2562 bp. The second one consisted of 12 exons and 11 introns with stop codon at position 1187 bp with 7th exon. The shortest transcript consisted of 10 exons and 9 introns with stop codon at 910 bp in the 7th exon. These premature stop codon might prevent the synthesis of fully active GHF74 or contribute for the production of protein with distinct function depending on the ambient carbon sources.

• Journal of Life Science
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• v.14 no.5
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• pp.752-760
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• 2004

The function of the [4Fe-4S] cluster containing iron (Fe-) protein in nitrogenase catalysis is to serve as the nucleotide-dependent electron donor to the MoFe protein which contains the sites for substrate binding and reduction. The ability of the Fe protein to function in this manner is dependent on its ability to adopt the appropriate conformation for productive interaction with the MoFe protein and on its ability to change redox potentials to provide the driving force required for electron transfer. The MgADP-bound (or off) conformational state of the nitrogenase Fe protein structure described reveals mechanisms for long-range communication from the nucleotide-binding sites to control affinity of association with the MoFe protein component. Two pathways, termed switches I and II, appear to be integral to this nucleotide signal transduction mechanism. In addition, the structure of the MgADP bound Fe protein provides the basis for the changes in the biophysical properties of the [4Fe-4S] observed when Fe protein binds nucleotides. The structures of the nitrogenase Fe protein with defined amino acid substitutions in the nucleotide dependent signal transduction pathways of the Switch I and Switch II have been determined by X-ray diffraction methods. These two pathways have been also implicated by site directed mutagenesis studies, structural analysis and analogies to other proteins that utilize similar nucleotide dependent signal transduction pathways. We have examined the validity of the assignment of these pathways in linking the signals generated by MgATP binding and hydrolysis to macromolecular complex formation and intermolecular electron transfer. The results provide a structural basis for the observed biophysical and biochemical properties of the Fe protein variants and interactions within the nitrogenase Fe protein-MoFe protein complex.

• Journal of the Korean Chemical Society
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• v.32 no.5
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• pp.436-442
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• 1988

The $^1H-nmr$ lineshapes of $H_2O$ in the solution containing $Al^{3+}$ ion have been measured as a function of temperature and $H^+$-ion concentration. Above [$H^+$] = 0.06, the lineshape were analyzed by the uncoupled two-site exchange model. From the proton exchange rate between hexaaquaaluminium ion and bulk water as a function of H-ion concentration. These kinetic data could be fitted to a following linear rate law; that is; 1/${\tau}$ = k$_1$/12 + $k_2$[$H^+$]/6. The following proton exchange parameters were obtained; $k_1^{298}$ = 38.5s$^{-1}$ ${\{Delta}H_1^{\neq}$ = $42.9kJ mole^{-1}$ ${\{Delta}S_1^{\neq}$ = -48.6J $mole^{-1}K^{-1}$ $k_2^{298}$ = $172s^{-1}mole^{-1}$ ${\{Delta}H_2^{\neq}$ = 27.8kJ $mole^{-1}$ ${\{Delta}S_2^{\neq}$ = -90.3J $mole^{-1}K^{-1}$ These activation parameters are indicating an associative interchange, Ia, mechanism for the acid-hydrolysis of hexaaquaaluminium ion and the proton exchange between the hydration spheres of $Al^{3+}$ and $H^+$.

• BMB Reports
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• v.35 no.3
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• pp.313-319
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• 2002

N-Acetyl-$\beta$-D-hexosaminidase ($\beta$-HexNAc'ase) (EC 3.2.1.52) was purified from rice seeds (Oryza sative L. var. Dongjin) using ammonium sulfate (80%) precipitation, Sephadex G-150, CM-Sephadex, and DEAE-Sephadex chromatography, sequentially. The activities were separated into 7 fractions($F_1-F_7$) by CM-Sephadex chromatography. Among them, F6 was further purified to homogeneity with a 13.0% yield and 123.3 purification-fold. The molecular mass was estimated to be about 52 kDa on SDS-PAGE and 37.4 kDa on Sephacryl S-300 gel filtration. The enzyme catalyzed the hydrolysis of both p-nitrophenyl-N-acetyl-$\beta$-D-hexosaminide (pNP-GlcNAc) and p-nitrophenyl-N-acetyl-$\beta$-D-hexosaminide (pNP-GalNAc) as substrates, which are typical properties of $\beta$-HexNAc'ase. The ratio of the pNP-GlcNAc'ase activity to the pNP-GalNAc'ase activity was 4.0. However, it could not hydrolyze chitin, chitosan, pNP-$\beta$-glucopyranoside, or pNP-$\beta$-glucopyranoside. The enzyme showed $K_m$, $V_{max}$ and $K_{cat}$ for pNP-GlcNAc of 1.65 mM, $79.49\;mM\;min^{-1}$, and $4.79{\times}10^6\;min^{-1}$, respectively. The comparison of kinetic values for pNP-GlcNAc and pNP-GalNAc revealed that the two enzyme activities are associated with a single binding site. The purified enzyme exhibited optimum pH and temperature for pNP-GlcNAc of 5.0 and $50^{\circ}C$, respectively. The enzyme activity for pNP-GlcNAc was stable at pH 5.0-5.5 and $20-40^{\circ}C$. The enzyme activity was completely inhibited at a concentration of 0.1 mM $HgCl_$ and $AgNO_3$, suggesting that the intact thiol group is essential for activity. Chloramine T completely inhibited the activity, indicating the possible involvement of methionines in the mechanism of the enzyme.

• Korean Chemical Engineering Research
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• v.45 no.5
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• pp.523-528
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• 2007

The objectives of this research are to investigate the mechanism of coagulation affecting UF, find out the effect of metal salt coagulant on membrane fouling. Either rapid mixing + UF or slow mixing + UF process caused much less flux decline. For PACl coagulant, the rate of flux decline was reduced for both hydrophilic and hydrophobic membrane than alum due to higher formation of flocs. In addition, the rate of flux decline for the hydrophobic membrane was significantly greater than for the hydrophilic membrane, regardless of pretreatment conditions. In general, Coagulation pretreatment significantly reduced the fouling of the hydrophilic membrane, but did little decrease the flux reduction of the hydrophobic membrane. When an Al(III) salt is added to water, monomers, polymers, or solid precipitates may form. Different Al(III) coagulants (alum and PACl) show to have different Al species distribution over a rapid mixing condition. During the rapid mixing period, for alum, formation of dissolved Al(III) (monomer and polymer) increases, but for PACl, precipitates of $Al(OH)_{3(s)}$ increases rapidly. This experimental results pointed out that precipitates of $Al(OH)_{3(s)}$ rather than dissolved Al(III) formation is major factor affecting flux decline for the membrane.

• Journal of Life Science
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• v.8 no.4
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• pp.410-415
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• 1998

Procine pepsin hydrolysis of hexapeptide L-S-pNF-Nle-A-OMe in the presence of dipeptide L-L generates a new peak on HPLC analysis of reaction mixtures that is not seen when enzyme is incubated with either peptide alone. The peaks can be detected spectroscopically at either 214 or 254 nm, the latter consistent with a new peptide containing the p-nitro-F residue. The data suggest acyl transpeptidation between E(L-S-pNF) and L-L to form L-S-pNF-L-L. Consistent with this inference are (1) the ability of L-L-NH$_{2}$ and inability of Boc-L-L to undergo a similar transpeptidation reaction, and (2) the data from electrospray mass spectrum. This synthesis requires that Nle-A-L-OMe be released before L-S-pNF, an order opposite to that proposed on the basis of product inhibition kinetics. Consistent with this inference are reciprocal solvent isotope effects ; normal isotope effects of 1.736$\pm$0.121 on the formation of Nle-A-L-OMe and 2.281$\pm$0.184 in the formation of L-S-pNF, coupled to an inverse isotope effects of 0.576$\pm$0.045 on the formation of L-S-pNF-L-L. Because transpeptidation precedes faster in D$_{2}$O, the isotopically-sensitive step must occur after release of Nle-A-L-OMe. Isotopically-enhanced transpeptidation is consistent with the Uni-Bi iso memchanism postulated on the basis of an isotope effects on Vmax but not on Vmax/Km$^{1)}$ and confirmed by isotope effects on the onset of inhibition by pepstatin$^{2)}$.