• Bulletin of the Korean Chemical Society
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• v.24 no.12
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• pp.1799-1804
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• 2003

Acetolatate synthase(ALS) catalyzes the first common step in the biosynthesis of valine, leucine, isoleucine in plants and microorganisms. ALS is the target of several classes of herbicides, including the sulfonylureas, the imidazolinones, and the triazolopyrimidines. To elucidate the roles of arginine residues in tobacco ALS, chemical modification and site-directed mutagenesis were performed. Recombinant tobacco ALS was expressed in E. coli and purified to homogeneity. The ALS was inactivated by arginine specific reagents, phenylglyoxal and 2,3-butanedione. The rate of inactivation was a function of the concentration of modifier. The inactivation by butanedione was enhanced by borate, and the inactivation was reversible on removal of excess butanedione and borate. The substrate pyruvate and competitive inhibitors fluoropyruvate and phenylpyruvate protected the enzyme against inactivation by both modifiers. The mutation of well-conserved Arg198 of the ALS by Gln abolished the enzymatic activity as well as the binding affinity for cofactor FAD. However, the mutation of R198K did not affect significantly the binding of FAD to the enzyme. Taken together, the results imply that Arg198 is essential for the catalytic activity of the ALS and involved in the binding of FAD, and that the positive charge of the Arg is crucial for the interaction with negatively charged FAD.

• BMB Reports
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• v.31 no.4
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• pp.399-404
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• 1998

In order to gain further insight on the relationship between structure and function of glutathione S-transferase (GST), the six active-site mutants, R13T, K44T, Q51A, Q64A, S65A, and D98A, of human GST P1-1 were expressed in Escherichia coli and purified to electrophoretic homogeneity by affinity chromatography on immobilized GSH. The active-site mutants showed marked differences in substrate specificity. The substitution of Gln51 with threonine resulted in a drastic decrease in the specific activities to <10% of the wild-type value. The substitution of Arg13 with threonine resulted in more decreased specific activity toward cumene hydroperoxide and in the $I_{50}$ values of S-(2,4-dinitrophenyl) glutathione and benanstatin A. These results suggest that the substitution of Arg13 with threonine changes the conformation of the active site to increase the affinity for the product or electrophilic substrate. Lys44 seems to be in the vicinity of the H-site of hGST P1-1 or may contribute to some extents to the electrophile binding.

• Journal of Microbiology and Biotechnology
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• v.22 no.3
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• pp.339-342
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• 2012

This study describes the characterization of a new angiotensin I-converting enzyme (ACE) inhibitory peptide from a Korean traditional rice wine. After purification of the ACE inhibitor peptides with ultrafiltration, Sephadex G-25 column chromatography, and successively $C_{18}$ and SCX solid-phase extraction, reverse-phase HPLC, and size exculsion chromatography, two types of the purified ACE inhibitors with $IC_{50}$ values of 0.34 mg/ml and 1.23 mg/ml were finally obtained. The two purified ACE inhibitors (F-1 and F-2) were found to have two kinds of novel oligopeptides, showing very little similarity to other ACE inhibitory peptide sequences. The amino acid sequences of the two purified oligopeptides were found to be Gln-Phe-Tyr-Ala-Val (F-1) and Ala-Gly-Pro-Val-Leu-Leu (F-2), and their molecular masses were estimated to be 468.7 Da (F-1) and 357.7 Da (F-2), respectively. They all showed a clear antihypertensive effect on spontaneously hypertensive rats at a dosage of 500 mg/kg.

• Bulletin of the Korean Chemical Society
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• v.33 no.12
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• pp.4074-4078
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• 2012

The first step in the common pathway for the biosynthesis of branched chain amino acids is catalyzed by acetohydroxyacid synthase (AHAS). The AHAS is found in plants, fungi and bacteria. With an aim to identify new anti-tuberculosis drugs that inhibit branched chain amino acid biosynthesis, we screened a chemical library against Mycobacterium tuberculosis AHAS. The screening identified four compounds, AVS 2087, AVS 2093, AVS 2236, and AVS 2387 with $IC_{50}$ values of 0.28, 0.21, 3.88, and $0.25{\mu}M$, respectively. Moreover, these four compounds also showed strong inhibition against reconstituted AHAS with $IC_{50}$ values of 0.37, 0.26, 1.0, and $1.18{\mu}M$, respectively. The basic scaffold of the AVS group consists of 1-pyrimidin-2-yl-1H-[1,2,4]-triazole-3-sulfonamide. The most active compound, AVS 2387, showed the lowest total interaction energy -8.75 Kcal/mol and illustrates its binding mode by hydrogen bonding with $H_{\varepsilon}$ of Gln517 with the distance of $2.24{\AA}$.

• BMB Reports
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• v.32 no.6
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• pp.579-584
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• 1999

Mantis egg fibrolase (MEF-3) was purified from the egg cases of Tenodera sinensis using ammonium sulfate fractionation, gel filtration on Bio-Gel P-60, DEAE Affi-Gel blue gel affinity chromatogragphy, and MONO-Q anion-exchange chromatography. This protease had a molecular weight of 35,600 Da as determined by SDS-polyacrylamide gel electrophoresis under reducing conditions and its isoelectric point was 6.0. The N-terminal amino acids sequence was Ala-Thr-Gln-Asp-Asp-Ala-Pro-Pro-Gly-Leu-Ala-Arg-Arg. This sequence was 80% homologous to the serine protease from Tritirachium album. MEF-3 readily digested the ${\alpha}$-and ${\beta}$-chains of fibrinogen and more slowly the ${\gamma}$-chains. It showed strong proteolytic and fibrinolytic activities. Phenylmethanesulfonyl fluoride and chymostatin inhibited its proteolytic activity, while EDTA, EGTA, cysteine, ${\beta}$-mercaptoethanol, elastinal, tosyl-lysine chloromethylketone, and tosyl-amido-2-phenylethyl chloromethyl ketone did not affect its proteolytic activity. Among the chromogenic protease substrates, the most sensitive one to the hydrolysis of MEF-3 was benzoyl-Phe-Val-Arg-p-nitroanilide. Based on these experimental results, we speculated that MEF-3 is a serine protease with a strong fibrin(ogen)olytic activity.

• Journal of Marine Bioscience and Biotechnology
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• v.10 no.1
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• pp.1-8
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• 2018

The objective of this study was to purify and characterize the ${\beta}-secretase$ inhibitor from enzymatic hydrolysates of blackfin flounder muscle, for development of a novel anti-dementia agent that may be used in the drug or functional food industries. ${\beta}-secretase$ inhibitory peptide was purified from various enzymatic hydrolysates of blackfin flounder muscle. Among six enzymatic hydrolysates, the Alcalase hydrolysate revealed highest ${\beta}-secretase$ inhibitory activity. Consecutive purification of the blackfin flounder muscle hydrolysate using Sephadex G-25 column chromatography and octadecylsilane C18 reversed phase HPLC techniques were used to isolate a potent ${\beta}-secretase$ inhibitory peptide composed of 5 amino acids, Leu-Thr-Gln-Asp-Trp (MW: 526.7 Da). The $IC_{50}$ value of purified ${\beta}-secretase$ inhibitory peptide was $126.93{\mu}M$. Results of this study suggest that peptides derived from blackfin flounder muscle may be beneficial as anti-dementia compounds in functional foods or as pharmaceuticals.

• Food Science of Animal Resources
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• v.36 no.4
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• pp.487-493
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• 2016

The antimicrobial activity of bovine lactoferrin hydrolysates (bLFH) was measured against Pseudomonas strains (P. syringae and P. fluorescens) in vitro. To compare susceptibility to bLFH, minimal inhibitory concentration (MIC) values were determined using chemiluminescence assays and paper disc plate assays. Antimicrobial effect against P. fluorescens was not observed by either assay, suggesting that bLFH did not exhibit antimicrobial activity against P. fluorescens. However, a significant inhibition of P. syringae growth was observed in the presence of bLFH. The addition of bLFH in liquid or solid medium inhibited growth of P. syringae in a dose-dependent manner. Furthermore, a bLFH peptide with antimicrobial activity toward P. syringae was isolated and identified. The N-terminal amino acid sequences of thus obtained antimicrobial bLFH peptides were analyzed by a protein sequencer and were found to be Leu-Arg-Ile-Pro-Ser-Lys-Val-Asp-Ser-Ala and Phe-Lys-Cys-Arg-Arg-Trp-Gln-Trp-Arg-Met. The latter peptide sequence is known to be characteristic of lactoferricin. Therefore, in the present study, we identified a new antimicrobial peptide against P. syringae, present within the N-terminus and possessing the amino acid sequence of Leu-Arg-Ile-Pro-Ser-Lys-Val-Asp-Ser-Ala.

• Bulletin of the Korean Chemical Society
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• v.28 no.3
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• pp.379-385
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• 2007

Receptor-oriented pharmacophore-based in silico screening is a powerful tool for rapidly screening large number of compounds for interactions with a given protein. Inhibition of the enzyme catechol-Omethyltransferase (COMT) offers a novel possibility for treating Parkinson's disease. Bisubstrate inhibitors of COMT containing the adenine of S-adenosylmethionine (SAM) and a catechol moiety are a new class of potent and selective inhibitor. In the present study, we used receptor-oriented pharmacophore-based in silico screening to examine the interactions between the active site of human COMT and bisubstrate inhibitors. We generated 20 pharmacophore maps, of which 4 maps reproduced the docking model of hCOMT and a bisubstrate inhibitor. Only one of these four, pharmacophore map I, effectively described the common features of a series of bisubstrate inhibitors. Pharmacophore map I consisted of one hydrogen bond acceptor (to Mg2+), three hydrogen bond donors (to Glu199, Glu90, and Gln120), and one hydrophobic feature (an active site region surrounded by several aromatic and hydrophobic residues). This map represented the most essential pharmacophore for explaining interactions between hCOMT and a bisubstrate inhibitor. These results revealed a pharmacophore that should help in the development of new drugs for treating Parkinson's disease.

• BMB Reports
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• v.37 no.5
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• pp.597-602
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• 2004

N-terminal His-tagged recombinant $\beta$-1,4-galactosyltransferase from Neisseria meningitidis was expressed and purified to homogeneity by column chromatography using Ni-NTA resin. Mutations were introduced to investigate the roles of, Ser68, His69, Glu88, Asp90, and Tyr156, which are components of a highly conserved region in recombinant $\beta$-1,4 galactosyltransferase. Also, the functions of three other cysteine residues, Cys65, Cys139, and Cys205, were investigated using site-directed mutagenesis to determine the location of the disulfide bond and the role of the sulfhydryl groups. Purified mutant galactosyltransferases, His69Phe, Glu88Gln and Asp90Asn completely shut down wild-type galactosyltransferase activity (1-3%). Also, Ser68Ala showed much lower activity than wild-type galactosyltransferase (19%). However, only the substitution of Tyr156Phe resulted in a slight reduction in galactosyltransferase activity (90%). The enzyme was found to remain active when the cysteine residues at positions 139 and 205 were replaced separately with serine. However, enzyme reactivity was found to be markedly reduced when Cys65 was replaced with serine (27%). These results indicate that conserved amino acids such as Cys65, Ser68, His69, Glu88, and Asp90 may be involved in the binding of substrates or in the catalysis of the galactosyltransferase reaction.

• KSBB Journal
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• v.28 no.3
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• pp.185-190
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• 2013

For the selection of peptide specifically binding to $Pb^{2+}$, the biopanning with the commercially available Ph.D.-7 phage displayed heptapeptide library was carried out against $Pb^{2+}$ immobilized on a metal-chelating IDA (iminodiacetic acid) resin. After four rounds of screening against $Pb^{2+}$-IDA including negative selections against charged bead with metal ions other than $Pb^{2+}$ and uncharged bead, several candidate lead-binding phage peptides were initially determined based on the order of frequency from the screened phage clones. Of the selected phage peptide sequences, the peptide of the highest frequency, CysSerIleArgThrLeuHisGlnCys (CSIRTLHQC) also exhibited the strongest affinity for $Pb^{2+}$ in binding assays for individual phage clones. However, there was not a significant difference in $Pb^{2+}$ affinity between selected peptides when using synthetic heptapeptides corresponding to the displayed peptide sequences of phage clones.