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J S Rhee

Publications and source records attributed to J S Rhee.

68 records · Page 4Linked to original sources
PubMed1994

Characterization and evaluation of a pta (phosphotransacetylase) negative mutant of Escherichia coli HB101 as production host of foreign lipase.

In order to evaluate the pta(phosphotransacetylase) (-) mutant of Escherichia coli as a potential host of foreign lipase expression, the pta(-) mutant HB101 was constructed for the purpose of blocking the acetate synthetic pathway. Since acetate is known as a major inhibitory by-product of cell growth and foreign protein production, the growth characteristics and expression kinetics of the microbial lipase of the pta(-) E. coli mutant were investigated. The growth rate was considerably decreased (about 30%) when grown on M9 minimal media containing glucose, mannose or glycerol. Growth retardation was not observed when a gluconeogenic carbon source (acetate, malate or succinate) was utilized. It should be noted that the growth rate of the mutant was enhanced (about 20%) in modified M9 media including a gluconeogenic carbon source and NZ-amine. Growth inhibition of the pta(-) mutant by menadione, a representative redox-cycling drug, was more pronounced than that of the parental type of E. coli. Furthermore, the inhibition effect was more pronounced in glucose minimal medium, whereas the menadione sensitivity was not observed when a gluconeogenic carbon source was used as a sole carbon source or the lactate dehydrogenase gene from Lactobacillus casei was introduced in the pta(-) mutant. Therefore, it is suggested that the growth deficiency of the pta(-) mutant is closely related to the intracellular redox balance. When the pseudomonad lipase was expressed in the pta(-) mutant, a comparable expression rate and yield to the parental type strain was observed. High-cell-density culture of the mutant was easy to achieve even under the fluctuating conditions of residual glucose concentration.

Acetates↗
PubMed1994

Gramicidin perforated patch-clamp technique reveals glycine-gated outward chloride current in dissociated nucleus solitarii neurons of the rat.

1. The inhibitory response of exogenously applied glycine was investigated in freshly dissociated rat nucleus tractus solitarii neurons under whole cell configuration using new perforated patch-clamp technique termed "gramicidin perforated patch technique," which maintains intact intracellular Cl- concentrations. 2. Using the gramicidin perforated patch technique, at a holding potential (VH) of -45 mV, glycine induced outward currents in a concentration-dependent manner with a EC50 of 4.0 x 10(-5) M and at a Hill coefficient of 1.5. In contrast, using the nystatin perforated patch technique, glycine induced inward currents at the same VH in a concentration-dependent manner with an EC50 of 4.9 x 10(-5) M and at a Hill coefficient of 1.2. 3. The glycine-induced outward currents were blocked by strychnine in a concentration dependent manner with an IC50 of 2.2 x 10(-8) M. The blockade was competitive. 4. The current-voltage relationship for the 10(-5) M glycine response showed a clear outward rectification. 5. Ten-fold change of extracellular Cl- with a large impermeable anion resulted in a 65 mV shift of the reversal potential of glycine-induced currents (EGly), indicating that the membrane behaves like a Cl- electrode in the presence of glycine. 6. The intracellular Cl- activity calculated from the EGly ranged from 7.3 to 18.2 mM, with a mean value of 13.3 mM. 7. The values of EGly in the individual neurons were significantly negative to the resting membrane potentials, suggesting the existence of active transport of Cl-.

Animals↗
PubMed1993

Purification and characterization of Pseudomonas fluorescens SIK W1 lipase expressed in Escherichia coli.

Pseudomonas fluorescens SIK W1 lipase was expressed as a form of inclusion bodies in Escherichia coli, which was equivalent to 46% of total cell protein. The inclusion bodies isolated from other cell components were solubilized in the buffer containing 8 M urea and then refolded by diluting urea. The lipase with active conformation was purified by hydrophobic interaction chromatography, gel filtration, anion-exchange chromatography and hydroxyapatite chromatography from the refolded sample. By these purification steps, a single band for active lipase was detected on non-reducing SDS-PAGE and 10-fold purification was attained on the basis of specific activity. Specific activity of the purified lipase toward olive oil emulsion was found to be 7395 units per mg protein. The optimum pH and temperature of the lipase were pH 8.5 and 45-55 degrees C, respectively. The lipase showed higher lipolytic activity toward tricaproin (C6) and tricaprylin (C8) among the triacylglycerols examined and preferentially hydrolyzed ester bond of 1- and 3-position of triolein. Lipase activity was greatly increased by approx. 6-fold and stability for pH was shifted to alkaline pH by Ca2+ ion. The lipase was inhibited by Hg2+, Ag2+, p-chloromercuribenzoate, diethylpyrocarbonate and sodium dodecyl sulfate.

Amino Acid Sequence↗
PubMed1992

Controlled mycelial growth for kojic acid production using Ca-alginate-immobilized fungal cells.

Conidia of Aspergillus oryzae were immobilized in Ca-alginate beads and then incubated in a nutrient medium to yield an immobilized biocatalyst producing kojic acid. The immobilized cell cultures produced kojic acid linearly during cultivation. Regardless of the size of the immobilized particles, there existed an optimal nitrogen concentration for the maximum production rate of kojic acid, at which smaller bead sizes resulted in a higher production rate. When the growth of mycelia were confined within the bead surface and segregated from each other by gel material, they produced kojic acid with maximal catalytic activity and exhibited the highest conversion yield of glucose. The extent of mycelial segregation was especially higher in cultures of smaller bead particles, and the depth of mycelial growth was 150 to 250 microns from the gel bead surface in all cultures of different nitrogen concentrations and bead sizes. Therefore, for the maximum expression of catalytic activities of immobilized mycelial cultures, it was found very critical to optimally control the mycelial distribution in gel beads by the culture conditions affecting mycelial growth.

Alginates↗
PubMed1991

Cloning and nucleotide sequence of thermostable lipase gene from Pseudomonas fluorescens SIK W1.

A gene coding for a thermostable lipase of Pseudomonas fluorescens SIK W1 was cloned into Escherichia coli JM83 by inserting Sau3AI-generated DNA fragments into the BamHI site of pUC19. Twenty colonies with esterase activity on the tributyrin agar plate were isolated by screening the constructed Pseudomonas fluorescens genomic library. Only one out of the esterase positive 20 colonies had lipase activity on the agar plate containing olive oil and Rhodamine-B. The complete nucleotide sequence of the lipase gene was identified. The lipase gene consists of an open reading frame, 1347bp long, commencing with an ATG start codon encoding a polypeptide of 449 amino acid residues and a TGA stop codon. Comparison of this lipase amino acid sequence with those from another organisms sequenced to data showed the presence of the short homologous region Gly-X-Ser-X-Gly.

Amino Acid Sequence↗
PubMed1990

Structure and function of the photoreceptor stentorins in Stentor coeruleus. I. Partial characterization of the photoreceptor organelle and stentorins.

The unicellular ciliary protozoan, Stentor coeruleus, exhibits photophobic and phototactic responses to visible light stimuli. The pigment granule contains the photoreceptor chromoproteins (stentorins). Stentorin localized in the pigment granules of the cell serves as the primary photoreceptor for the photophobic and phototactic responses in this organism. An initial characterization of the pigment granules has been described in terms of size, absorbance spectra and ATPase activity. Two forms of the stentorin pigments have been isolated from the pigment granules. Stentorin I has an apparent molecular weight of 68,600 and 52,000 by SDS-PAGE (at 10 and 13% gel, respectively) or 102,000 by steric exclusion HPLC, whereas stentorin II is a larger molecular assembly probably composed of several proteins (mol. wt. greater than 500,000). Stentorin I is composed of at least two heterologous subunits corresponding to apparent mol. wts. of 46,000 (fluorescent, Coomassie blue negative) and 52,000 (fluorescent, Coomassie blue positive) on SDS-PAGE (13% gel). However, these values were found to be strongly dependent on the degree of crosslinking in the acrylamide gel. Stentorin II appears to be the primary photoreceptor whose absorption and fluorescence properties are consistent with the action spectra for the photoresponses of the ciliate to visible light.

Animals↗
PubMed1990

Cloning and nucleotide sequence of an esterase gene from Pseudomonas fluorescens and expression of the gene in Escherichia coli.

A gene coding for a novel esterase of Pseudomonas fluorescens was cloned in this study. DNA sequencing showed that the open reading frame is comprised of 708 nucleotides. The coding sequence of the gene is preceded by a potential Shine-Dalgarno sequence and by a promoter-like structure. Following the stop codon a structure reminiscent of the E. coli rho-independent terminator is present. The enzyme expressed in an E. coli clone was mostly in the periplasmic space, released to the outside of the cell by osmotic shock and purified to homogeneity by QAE-Sephadex A-50 and DEAE-Sepharose columns. The native form of the enzyme consisted of two identical subunits, each with a molecular weight of 27,000. By studying the properties and substrate specificity, the enzyme was classified as an arylesterase (EC 3.1.1.2).

Amino Acid Sequence↗
PubMed1984

Effects of organic solvents on lipase for fat splitting.

The effect of organic solvents on the stability and catalytic activity of the microbial lipase from Candida rugosa for hydrolysis of triglyceride (fat splitting) has been examined. The solvents examined were 5 hydrocarbons (n-hexane, n-heptane, n-octane, iso-octane and cyclohexane) and 3 ethers (diethyl-ether, diisopropylether and di-n-butylether). The results revealed that iso-octane and cyclohexane are superior to the other solvents examined for enzymatic fat splitting in organic solvent systems.

Candida↗
PubMed1980

Enzymatic biosynthesis of cephalexin.

The reaction kinetics of the enzymatic synthesis of cephalexin from 7-aminodeacetoxy cephalosporanic acid and phenylglycine methylester was studied using the synthesizing enzyme obtained from Xanthomonas citri. The activation energy, Km values for 7-aminodeacetoxy cephalosporanic acid and phenylglycine methylester, and Ki value for phenylglycine methylester were determined as 8.63 kcal/mol, 3.7mM, 14.5mM, and 70mM, respectively. The enzyme was found to be constitutive and susceptible to deactivation.

Amidohydrolases↗
PubMedDate not supplied

Intranasal endoscopy-assisted repair of medial orbital wall fractures.

The repair of medial orbital blow-out fractures remains a challenging surgical procedure for most surgeons. Endoscopic intranasal visualization of the medial orbital wall or lamina papyracea is a technique familiar to most otolaryngologists. This endoscopic view would allow for confirmation of orbital content reduction and bimanual manipulation of an orbital implant. To determine the effectiveness of a new surgical technique, a cadaveric study was performed to evaluate the ability to (1) reduce the herniated orbital contents and (2) restore the normal anatomic orbital configuration and volume with the addition of an orbital implant. Excellent visualization of the fracture was achieved in all cadaveric specimens. In addition, endoscopic intranasal visualization of the medial orbital wall greatly facilitated the anatomic reduction of orbital contents and proper placement of the orbital implant. The surgical technique is described and a clinical case is reported in which this endoscopic technique was effectively used. Arch Facial Plast Surg. 2000;2:269-273

Adult↗
PubMedDate not supplied

Management of misplaced or migrated endovascular stents.

PURPOSE: To report experience with techniques for management of misplaced or migrated endovascular stents. MATERIALS AND METHODS: During a 5-year period, percutaneous management of 27 misplaced or migrated endovascular stents (16 Palmaz, 11 Wallstents) in 25 patients was attempted. The 17 venous and 10 arterial stents were rescued from the aorta (n = 9), inferior vena cava (IVC) (n = 4), transjugular intrahepatic portosystemic shunt/IVC (n = 2), right atrium (n = 3), right ventricle (n = 2), pulmonary artery (n = 2), iliac vein (n = 2), iliac artery (n = 1), superior vena cava (n = 1), and superior mesenteric vein (n = 1). RESULTS: Stent management was successful in 26 of 27 cases (96%). Eleven stents were removed percutaneously, two were repositioned and removed with a minor surgical procedure, and 13 were repositioned and deployed in a stable alternate location. The only complication was the development of tricuspid insufficiency in the single case in which the procedure failed (4% complication rate). This patient's stent was eventually surgically removed from the right ventricle. CONCLUSION: Misplaced or migrated endovascular Palmaz and Wallstents can be effectively managed with few complications by using a variety of percutaneous techniques.

Adult↗
PubMedDate not supplied

Effects of growth rate on the production of Pseudomonas fluorescens lipase during the fed-batch cultivation of Escherichia coli.

Recombinant Escherichia coli was grown to produce the thermostable Pseudomonas fluorescens lipase by controlling the specific growth rate (mu). At low growth rate (mu = 0.07 h-1), a higher cell density (OD600 = 140) was obtained. By calculating the cell yield on nitrogen, the medium was optimized to prevent inhibition of cell growth by nitrogen unbalance. Acetate accumulated in the broth at the same rate as observed in a chemostat under nitrogen-limited fed-batch conditions, but not in a glucose-limited fed-batch culture. Postinduction growth rate affected lipase production more than preinduction growth rate. After induction, more lipase was produced at a low growth rate (mu = 0.1 h-1) than at a high growth rate (mu = 0.4 h-1). More lipase was produced at 37 than at 20 degrees C at a constant growth rate, indicating that temperature affected other factors in addition to growth rate.

Acetic Acid↗