• Toxicological Research
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• v.21 no.4
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• pp.319-323
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• 2005

The aim of the present study was to evaluate systemic bioavailability of surfactin and to determine its pharmacokinetic profiles. The stability of surfactin to pH, temperature and protease was evaluated. Surfactin was resistant to high temperature, a wide range of pH and the action of hydrolytic enzymes. The pharmacokinetic natures of surfactin which were shown the short half-life, rapid clearance and poor bioavailability. The results of study should provide preliminary data of surfactin for further dose-finding studies and for the design of application forms. It is also be important to a context of the safety of surfactin.

• Journal of Life Science
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• v.21 no.5
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• pp.761-765
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• 2011

Salt stability of enzymes is a crucial practical factor in the food industry. Previously, leucine aminopeptidase (LAP) was purified from Bacillus sp. N2. Here, we present the salt effect of LAP using synthetic substrates. LAP had a hydrolytic activity for L-leucine-${\rho}$-nitroanilide in high concentrations of NaCl (up to 4 M), but not for other neutral salts (LiBr, LiCl, NaBr, KBr, and KCl). It hydrolyzed various synthetic di-peptide substrates with hydrophobic and hydrophilic amino acids at the C-terminal Xaa region, in the presence of 0-4 M NaCl. The result indicated that the hydrolytic action of LAP is not dependent on the hydrophobicity of the amino acid side chain at the scissile bond of the substrate. Remarkably, the hydrolytic activity of LAP was 1-3 folds higher than those of other LAPs and aminopeptidases in 4.5 M NaCl, suggesting that NaCl-tolerant LAP might be used in the food industry as cheese and anchovy sauce.

• Journal of Microbiology and Biotechnology
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• v.16 no.1
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• pp.145-148
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• 2006

A new functional lipolytic enzyme (AT4) has recently been found from Agrobacterium tumefaciens C58 Cereon using a genome-wide approach. The enzyme has some sequence similarity to E. coli acetyl hydrolase, Emericella nidulans lipase, Moraxella sp. lipase, Acinetobacter lwoffii esterase, and Streptomyces hygroscopicus acetyl hydrolase. However, the sequence similarities are very low (less than $25\%$), suggesting that it is a new lipase/esterase enzyme. ill the present study, intact cell of the A. tumefaciens strain was shown to have lipolytic activity on a tributyrin-LB plate. The AT4 gene was then expressed at a high level in E. coli BL21 (DE3) cells and the enzyme was purified simply by Ni-NTA column chromatography. The purified enzyme showed hydrolytic activity toward p-nitrophenyl caproate, but not toward olive oil, suggesting that the AT4 enzyme was a typical esterase rather than lipase. AT4 esterase had a maximum hydrolytic activity at $45^{\circ}C$ and pH 8.0, when p-nitrophenyl caproate was used as a substrate. It was relatively stable up to $40^{\circ}C$ and at pH 5.0-9.0. Calcium ion and EDT A did not affect the activity and thermal stability of the enzyme. As for substrate specificity, AT4 enzyme could rapidly hydrolyze acetyl and butyl groups from p-nitrophenyl esters and 1-naphthyl esters. In addition, it also released acetyl residues from acetylated glucose and xylose substrates. Therefore, this new esterase enzyme might be used as a biocatalyst in acetylation and deacetylation reactions performed in the fine chemical industry.

• Microbiology and Biotechnology Letters
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• v.32 no.1
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• pp.78-83
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• 2004

In order to screen microorganisms producing phopholipase D (PLD) had high transphosphatidylation activity, about 1,000 Actinomycetes strains were isolated from the 63 soil samples, collected over 6 local area in Korea. When the hydrolytic activity in the supernatant was determined, 131 strains produced PLD more than 0.3U/$m\ell$. Among 131 culture broths tested, 23 ones had transphosphatidylation activity higher than 20% and finally one strain (Actinomycetes KF923), which had highest hydrolytic and transphophadylation activity, was selected. Actinomycetes KF923 showed the highest hydrolytic activity (13U/$m\ell$) and phosphatidylation activity (95%) after 48 h fermentation using the P medium (yeast extract 1%, peptone 1%, glucose 1.5%, glycerol 1%, $CaCO_3$ 0.4%, pH 7.2). PLD was purified from the culture broth of Actinomycetes KF923 and the specific activity of purified PLD was 567U/mg. The molecular weight of PLD was about 55kD and the optimum pH and temperature were pH 6.0 and $60^{\circ}C$, respectively. The stability of PLD toward pH and temperature were high around pH 8.0 and below $40^{\circ}C$ Special metal ions were not necessary to the PLD activity.

• Microbiology and Biotechnology Letters
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• v.31 no.4
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• pp.389-394
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• 2003

In order to screen microorganisms producing phopholipase D (PLD) had high transphosphatidylation activity, about 1,000 Actinomycetes strains were isolated from the 63 soil samples, collected over 6 local area in Korea. When the hydrolytic activity in the supernatant was determined, 131 strains produced PLD more than 0.3 U/ml. Among 131 culture broths tested, 23 ones had transphosphatidylation activity higher than 20% and finally one strain (Actinomycetes KF 923), which had highest hydrolytic and transphophadylation activity, was selected. Actinomycetes KF923 showed the highest hydrolytic activity (13 U/ml) and phosphatidylation activity (95%) after 48 h fermentation using the P medium (yeast extract 1%, peptone 1%, glucose 1.5%, glycerol 1%, $CaCo_3$ 0.4%, pH 7.2). PLD was purified from the culture broth of Actinomycetes KF923 and the specific activity of purified PLD was 567 U/mg. The molecular weight of PLD was about 55 kD and the optimum pH and temperature were 6.0 and $60^{\circ}C$, respectively. The stability of PLD toward pH and temperature were high around pH 8.0 and below $40^{\circ}C$. Special metal ions were not necessary to the PLD activity.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2006.04a
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• pp.180-181
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• 2006

The hydrolysis of some vinylsulfonyl (VS) typed reactive dyes were investigated at the pH, temperature and other experimental conditions. The hydrolytic behaviour, especially, stability in various pH value, of the water soluble reactive dyes are examined. In neutral and acid condition, mother dyes are a quite stable. Other hand, it was found that dimerization and decomposition for these dyes were estimated in an aqueous alkaline medium. These alkaline hydrolysis behaviour was monitored by the high performance liquid chromatography.

• Proceedings of the KACD Conference
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• 2003.11a
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• pp.605-605
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• 2003

Novel silane coupling agents containing hydrophobic phenyl group 3-(3-methoxy-4-methacryloyloxyphenyl) propyl-trimethoxysilane(p-MPS), -triisocyanatesilane (p-MBI), -trichlorosilane (p-MBC) were synthesized. The bonding durability of these silanes against water immersion and thermal stress was investigated. 3-methacryloyloxypropyltrimethoxysilane (3-MPG) was used as a control. The glass modified with those silanes at a concentration of 2wt％ were kept for 3 minutes at $120^{\circ}C$, and then were bonded to the heaped metal with self-cured resin composite.(omitted)

• Proceedings of the Membrane Society of Korea Conference
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• 2003.11a
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• pp.61-63
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• 2003

A major research objective related to proton exchange membrane(PEM) for DMFC is to achieve high proton conductivity over 10$^{-2}$ S/cm, high hydrolytic stability and low methanol permeability with low cost base materials. for the purpose, a lot of thermoplastic polymers such as polysulfones, polyethersulfone, polyetherketones, polyimides, polyoxadiazole, polyphosphazene and polybenzimidazol have been investigated. Amongst those polymers, polyimides have been suggested as a potential PEM due to their excellent thermal, chemical stability and good mechanical properties. Generally, polyimides are synthesized by polycondensation with numerious diamines and dianhydriedes. In our study, polyimide was prepared using non-sulfonated diamine, sulfonated diamine directly synthesized by fuming sulfuric acid, and naphthalenic dianhydride to improve the hydrolysis stability under acidic condition. Through monomer sulfonation-subsequent polymerization method, the high proton conducting capability and the desired sulfonation level were effectively controlled at the same time. To reduce severe methanol transport through the membrane, the chemical crosslinking among polymer chains was introduced using various crosslinking agents with different chain lengths. The crosslinked sulfonated polyimide membranes showed high proton conductivity up to 8.09$\times$10$^{-2}$ S/cm and from crosslinking effect methanol transport through the membranes was considerably reduced as compared with unmodified membranes. For increase of chain length of crosslinker, methanol permeability was adversely reduced to 10$^{-8}$ $\textrm{cm}^2$/s due to decrease of IEC and increase of crosslinking desity.

• Journal of Microbiology and Biotechnology
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• v.20 no.2
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• pp.325-331
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• 2010

Rhodococcus erythropolis amidase was expressed in Escherichia coli cells. The crude amidase in the cell-free extract was immobilized using the cross-linked enzyme aggregate (CLEA) method. The crude amidase was mixed with bovine serum albumin and then precipitated with ammonium sulfate. The resultant precipitant was subsequently cross-linked with glutaraldehyde. Scanning electron microscopy revealed that this co-CLEA had a ball-like shape with a diameter of approximately $1\;{\mu}m$. This co-CLEA evidenced hydrolytic activity toward a variety of amide substrates. The amidase co-CLEA evidenced an optimum temperature of $60^{\circ}C$ and an optimum pH of 8.0, results that were similar to those of the soluble amidase. The reaction stability of the co-CLEA was increased. That is, it was stable up to $50^{\circ}C$ and in a pH range of 5.0-12.0. Additionally, the co-CLEA could be recovered by centrifugation, and retained 96% activity after 3 repeated cycles. This amidase co-CLEA may prove useful as a substitute for soluble amidase as a biocatalyst in the pharmaceutical and chemical industries.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.3
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• pp.62-69
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• 1998

Mechanical properties of polyethyleneglycol(PEG)/cyclo-tetramethylene tetranitramine(HMX) propellant were studied by adding polycaprolactone(PCP) and silane derivatives as coupling agent. Mechanical properties of the propellant were enhanced by increasing the content of PCP which was partially replaced with PEG. PCP/HMX propellant showed 17% increase in maximum tensile strength and 59% increase in elongation compared to those of PEG/HMX propellant. However, as the content of PCP was increased, the hydrolytic stability of this propellant was found to be deteriorated due to the ester group of PCP by measuring hardness drop of cured propellant and swell ratio difference of PEG/PCP binder stored at $40^{\cire}C$ and 90% relative humidity. Hardness of the PEG/PCP/HMX propellant was decreased with increasing triethoxysilyl propionitrile(TESPN) and dinitrosalicylic acid (DNSA) content from accelerated aging at $60^{\cire}C$.