Biomedical subjects

Y J Choi

Publications and source records attributed to Y J Choi.

At least 73 records · Page 4Linked to original sources

PubMed1999

Steady-state oxidation model by horseradish peroxidase for the estimation of the non-inactivation zone in the enzymatic removal of pentachlorophenol.

A theoretical model for the rate of oxidation of pentachlorophenol (PCP) catalyzed by horseradish peroxidase (HRP), was investigated to account for the influence of hydrogen peroxide (H2O2) concentration on the catalytic activity. To evaluate the maximum allowable H2O2 concentration, a relatively simple steady-state model was developed based on the Ping-Pong Bi-Bi mechanism considering the effect of excess H2O2. Several sets of experimental data obtained from batch reactions using an equimolar concentration of H2O2 and PCP were used to estimate the kinetic parameters by a nonlinear regression method. The model profiles acquired using the estimated parameters were in good agreement with experimental data at different initial enzyme and substrate concentrations. The best-fitted parameters were used to predict the initial rate of the enzyme reaction. The model prediction was coincident with the experimental results of other studies, indicating that the proposed model could be used for the optimization of reaction conditions. The maximum allowable H2O2 concentration to prevent H2O2 inhibition was calculated from the proposed model equation: [H2O2](0,max) = (square root)KmH2O2Ki[PCP]0/KmPCP+[PCP]0. Using this equation, a curve depicting the non-inactivation zone for the two substrates (hydrogen peroxide and PCP) was plotted and it could be used for experimental design and optimal process operation. To minimize enzyme inactivation by H2O2, it was determined that the concentration of H2O2 should be lower than 2.78 mM, regardless of the stoichiometric ratio.

Journal Article↗

PubMed1999

Catabolite repression of the xylanase gene (xynA) expression in Bacillus stearothermophilus no. 236 and B. subtilis.

Catabolite repression of the Bacillus stearothermophilus No. 236 xynA gene, encoding an extracellular xylanase, was investigated in this work. Expression of the xynA gene in the B. stearothermophilus strain was found to be subject to glucose catabolite repression, and the level of repression was about 50-fold when the relative amounts of xynA transcript synthesized on different carbon sources were analyzed. The experiments with the B. subtilis MW15 strains carrying plasmids containing the xynA::aprA fusion gene showed that the cloned xynA gene did not require any specific carbon source for its induction. Nevertheless, the expression of the cloned gene was repressed by the presence of glucose. From the nucleotide sequence of the cloned xynA gene, we found two potential catabolite responsive elements (cre) within its reading frame region (cre-1: nucleotides +160 to +173 and cre-2: +173 to +186). Furthermore, by using various deletion derivatives of the xynA::aprA fusion plasmid (pMGW23), we suggested that only the cre-2 element might play a role in the glucose catabolite repression. Repression level of the xynA gene expression in the recombinant B. subtilis strain was estimated to be about 3-fold by analysis of the amounts of xynA transcript.

Bacillus subtilis↗

PubMed1999

Central retinal vein occlusion combined with cilioretinal artery occlusion.

A healthy 65-year-old man with sudden profound visual loss in his right eye presented with clinical signs of central retinal venous occlusion and retinal whitening, indicative of a cilioretinal arterial obstruction. He had been diagnosed with cilioretinal artery occlusion at a private ophthalmology clinic three days before being referred to our department. On fluorescein angiogram of the affected eye, the proximal portion of the retinal arteries filled with dye 27.3 seconds after injection, indicating a delay in retinal arterial filling. Moreover, the cilioretinal artery did not fill at that phase, but went on to fill 45.1 seconds after injection. Over 63.4 seconds after the filling of the retinal arteries, the laminar flow of the retinal venous vessels appeared. This was not until 90.7 seconds after injection. This patient was elderly, had no systemic diseases, and showed non-ischemic CRVO, prolonged retinal arterial filling on fluorescein angiography, and poor prognosis in visual acuity. His clinical course seemed to favor the pathogenetic hypothesis of a primary arterial affection.

Aged↗

PubMed1999

Differential transmission of G1 cell cycle arrest and mating signals by Saccharomyces cerevisiae Ste5 mutants in the pheromone pathway.

Saccharomyces cerevisiae Ste5 is a scaffold protein that recruits many pheromone signaling molecules to sequester the pheromone pathway from other homologous mitogen-activated protein kinase pathways. G1 cell cycle arrest and mating are two different physiological consequences of pheromone signal transduction and Ste5 is required for both processes. However, the roles of Ste5 in G1 arrest and mating are not fully understood. To understand the roles of Ste5 better, we isolated 150 G1 cell cycle arrest defective STE5 mutants by chemical mutagenesis of the gene. Here, we found that two G1 cell cycle arrest defective STE5 mutants (ste5M(D248V) and ste5(delta-776)) retained mating capacity. When overproduced in a wild-type strain, several ste5 mutants also showed different dominant phenotypes for G1 arrest and mating. Isolation and characterization of the mutants suggested separable roles of Ste5 in G1 arrest and mating of S. cerevisiae. In addition, the roles of Asp-248 and Tyr-421, which are important for pheromone signal transduction were further characterized by site-directed mutagenesis studies.

Adaptor Proteins, Signal Transducing↗

PubMed1998

Matrix attachment region sequences enhanced the expression frequency of a whey acidic protein/human lactoferrin fusion gene in the mammary gland of transgenic mice.

To elevate the expression frequency of transgenes in transgenic mice, the chicken lysozyme matrix attachment region (MAR) sequence was used by combining it with a transgene. The whey acidic protein (WAP) promoter/human lactoferrin (hLF) cDNA fusion transgene (pWL) was connected to the chicken lysozyme MAR sequence at its 5'-end (pMWL). While only two of three mice became transgenic from the pWL vector expressed hLF, all seven mice from the pMWL vector expressed the transgene in their lactating mammary glands. To evaluate the effect of lactogenic hormones on transgene expression, experiments with the primary culture of transgenic mammary explants were performed. It was revealed that the expression of transgenes was slightly increased by insulin plus dexamethasone or insulin plus prolactin treatment. However it was not increased by insulin, dexamethasone or prolactin (IDP) treatment alone. In contrast, the endogenous WAP gene was expressed only in the IDP treated group. These results demonstrate that MAR sequences are effective in improving the expression frequency of transgenes in transgenic mice although the developmental and hormonal regulations are not the same as those of the endogenous WAP gene.

Animals↗

PubMed1998

High-performance liquid chromatographic determination of a new oral thrombin inhibitor in the blood of rats and dogs.

A reliable reversed-phase high-performance liquid chromatographic method has been developed for the determination of a new oral thrombin inhibitor (compound I) in the blood of rats and dogs. The analyte was deproteinized with a 1.5 volume of methanol and a 0.5 volume of 10% zinc sulfate, and the supernatant was injected into a 5-microm Capcell Pak C18 column (150 x 4.6 mm I.D.). The mobile phase was a mixture of acetonitrile and 0.2% triethylamine of pH 2.3 (31:69, v/v) with a flow-rate of 1.0 ml/min at UV 231 nm. The retention time of compound I was approximately 9.3 min. The calibration curve was linear over the concentration range of 0.05-100 mg/l for rat blood (r2>0.9995, n=6) and dog blood (r2>0.9993, n=6). The limit of quantitation was 0.05 mg/l for both bloods using a 100-microl sample. For the 5 concentrations (0.05, 0.1, 1, 10, and 100 mg/l), the within-day recovery (n=4) and precision (n=4) were 98.1-104.1% and 1.5-6.8% for rat blood and 95.4-105.7% and 1.4-5.3% for dog blood, respectively. The between-day recovery (n=6) and precision (n=6) were 99.8-105.3% and 3.7-12.6% for rat blood and 87.5-107.1% and 2.9-15.3% for dog blood, respectively. The absolute recoveries were 82.4-93.3%. No interferences from endogenous substances were observed. In conclusion, the presented simple, sensitive, and reproducible HPLC method proved and was used successfully for the determination of compound I in the preclinical pharmacokinetics.

Administration, Oral↗

PubMed1998

Cloning of the 52-kDa chitinase gene from Serratia marcescens KCTC2172 and its proteolytic cleavage into an active 35-kDa enzyme.

A chitinase gene (pCHI52) encoding the 52-kDa chitinase was isolated from a Serratia marcescens KCTC2172 cosmid library. This chitinase gene consists of 2526 bp with an open reading frame that encodes 485 amino acids. Escherichia coli harboring the pCHI52 gene secreted not only a 52-kDa but also a 35-kDa chitinase into the culture supernatant. We purified both 52-kDa and 35-kDa chitinases using a chitin affinity column and Sephacryl-S-300 gel filtration chromatography. We determined that the 17 N-terminal amino acid sequences of the 52-kDa and the 35-kDa chitinase are identical. Furthermore, a protease obtained from S. marcescens KCTC2172 cleaved the 52-kDa chitinase into the 35-kDa protein with chitinase activity. These results suggest that the 35-kDa chitinase derives from the 52-kDa chitinase by post-translational proteolytic modification. The optimal reaction temperature of 45 degrees C and the optimal pH of 5.5 were identical for both enzymes. The specific activities of the 52-kDa and 35-kDa chitinases on natural swollen chitin were 67 mumol min-1 mg-1 and 60 mumol min-1 mg-1, respectively.

Amino Acid Sequence↗

PubMed1998

Pharmacokinetic changes of M1, M2, M3 and M4 after intravenous administration of a new anthracycline, DA-125, to rats pretreated with phenobarbital, 3-methylcholanthrene, chloramphenicol, or SKF-525A.

The pharmacokinetics of M1-M4, the metabolites of a new anthracycline antineoplastic agent, DA-125, were compared after intravenous (i.v.) administration of DA-125, 15 mg kg-1, to rats pretreated with enzyme inducers, such as phenobarbital (PBT, n = 14) and 3-methylcholanthrene (MCT, n = 15), or enzyme inhibitors, such as SKF-525A (SKT, n = 11) and chloramphenicol (CMT, n = 15), and to their control rats (n = 15 for PBC, CMC or SKC, and n = 11 for MCC). After i.v. administration of DA-125, the plasma concentrations of both M1 and M2 declined slowly from 1 to 2 h onwards to 8 h in all groups of rats due to the continuous formation of M2 from M1. The AUC0-8 h of M1 (47.1 versus 7.85 micrograms min mL-1) and M2 (20.7 versus 44.3 micrograms min mL-1) decreased significantly in the PBT group compared to those in the PBC group. However, the corresponding value of only M1 (74.6 versus 89.9 micrograms min mL-1) decreased significantly in the MCT group. The above data indicate that metabolism of M1 is increased by pretreatment with both PB and 3-MC, and that of M2 with PB, but not with 3-MC. The AUC0-8 h of both M1 (126 versus 78.5 micrograms min mL-1) and M2 (69.2 versus 44.3 micrograms min mL-1) increased significantly in the SKT group compared to the SKC group. However, the corresponding values were not significantly different between CMC and CMT groups. The above data indicate that the metabolism of both M1 and M2 is inhibited by pretreatment with SKF-525A, but not with CM.

Animals↗

PubMed1998

Recurrent parosteal osteosarcoma of the talus in a 2-year-old child.

Parosteal osteosarcoma is an uncommon, low-grade malignant bone tumor and is found in an older age group than conventional osteosarcoma. We present a talar parosteal osteosarcoma that recurred twice in a 2-year-old child. To our knowledge, this is the youngest patient reported with a parosteal osteosarcoma. The talus is an unusual site for parosteal osteosarcoma. Inadequate resection due to a diagnosis of juxtacortical chondroma resulted in recurrence of the tumor. The age of the patient, the thick cartilaginous cap, and well-differentiated trabecular bone all contributed to the critical erroneous diagnosis.

Bone Neoplasms↗

PubMed1998

A new class II rice chitinase, Rcht2, whose induction by fungal elicitor is abolished by protein phosphatase 1 and 2A inhibitor.

Among the four classes of chitinase, a class II chitinase had not yet been reported for rice. We have isolated and characterized a class II acidic chitinase, Rcht2, from rice (Oryza sativa L. cv. Cheongcheongbyeo). The protein consists of a single polypeptide chain of 261 amino acid residues and includes a putative signal sequence of 29 amino acids at its N-terminus. It has a calculated molecular mass of 27,642 Da and an isoelectric point of 5.56. The Rcht2 chitinase lacks the cysteine-rich and hinge domains in the N-terminal region of the protein, which is the criterion for its classification as a class II chitinase. Comparison of the genomic and the cDNA sequence revealed that the coding region of Rcht2 consist of three exons of 301, 112, and 370 bp separated by two introns of 89 and 984 bp. In suspension-cultured rice cells, the transcript level of Rcht2 was dramatically increased by treatment with both glycol chitin and fungal elicitor. The application of protein phosphatase 1 and 2A inhibitors, calyculin A and okadaic acid, effectively abolished the induction of Rcht2 in response to fungal elicitor. In contrast, the activation of Rcht2 transcript was not inhibited by both cycloheximide and protein kinase inhibitors. These results demonstrate that protein dephosphorylation events play a crucial role in the elicitor-mediated induction of Rcht2 in rice cells, while de novo protein synthesis is not required for induction.

Amino Acid Sequence↗

PubMed1998

Immunotactoid glomerulopathy associated with idiopathic hypereosinophilic syndrome.

A case of immunotactoid glomerulopathy in an 18-year-old man with an idiopathic hypereosinophilic syndrome is presented. The patient showed cervical lymphadenopathy, asymptomatic proteinuria of nephrotic range, and hematuria without any defined immunologic disease. Marked and prolonged hypereosinophilia was found in peripheral blood (eosinophil count; 6,248/mm3) and bone marrow (eosinophil series; 32%). Diffuse and/or nodular eosinophilic infiltration was identified in multiple organs such as kidney, stomach, liver, lymph node, and skin. Renal biopsy revealed endocapillary proliferative features of typical immunotactoid glomerulopathy with IgG and C3 deposition and microtubular structures of variable size, 20-80 nm in diameter, mainly in the subendothelium. This study suggests that immunotactoid glomerulopathy may be a secondary immunologic manifestation of the tissue damage by eosinophils in the idiopathic hypereosinophilic syndrome.

Adolescent↗

PubMed1998

Gene expression during involution of mammary gland (review).

After cessation of lactation, the mammary gland undergoes involution, regressing to a state resembling that of a virgin animal. This phase of mammary gland development is characterized by epithelial cell death and tissue remodeling. To understand molecular mechanisms of mammary gland involution, we identified involution-induced clones by differential screening of a mouse mammary gland cDNA library. Several known genes were induced during mammary gland involution: sulfated glycoprotein-2 (SGP-2), WDNM1, lactoferrin, ferritin heavy chain (FHC), lysozyme and osteopontin genes. Involution of the mammary gland is presumed to be mediated by a decrease in serum prolactin level induced by weaning, but may also involve changes in paracrine or autocrine growth factors. Effects of lactogenic hormones and EGF on the expression of the involution-induced genes were examined in mammary epithelial cells. Insulin, dexamethasone, and prolactin did not influence the expression of the FHC, WDNM1 and SGP-2 genes. However, EGF strongly inhibited the expression of WDNM1 and SGP-2 genes. Our recent results are reviewed and discussed.

Animals↗

PubMed1997

High-performance liquid chromatographic assay of a new HIV-1 protease inhibitor, LB71350, in the plasma of dogs.

A reliable reversed-phase high-performance liquid chromatographic method has been developed for the determination of LB71350 in the plasma of dogs. The analyte was deproteinized with 1.5 volumes of methanol and 0.5 volumes of 10% zinc sulfate, and the supernatant was injected into a 5-microm Capcell Pak C18 column (150x4.6 mm I.D.). The mobile phase was a stepwise gradient mixture of acetonitrile and 0.2% triethylamine-HCl with a flow-rate of 1 ml/min and detection at UV 245 nm. The proportion of acetonitrile was kept at 52% for the first 6 min, increased to 100% for the next 0.5 min, kept at 100% for the next 2 min, decreased to 52% for the next 0.5 min, and finally kept at 52% for the next 7 min. The retention time of LB71350 was 6.9 min. The calibration was linear over the concentration range of 0.1-100 mg/l for dog plasma (r>0.997) and the limit of quantitation was 0.1 mg/l using 0.1 ml plasma. The quality control samples were reproducible with acceptable accuracy and precision at 0.1, 1, 10 and 100 mg/l concentrations. The within-day recovery (n=5) was 90.2-93.9%, the between-day recovery (n=5) was 89.5-93.5%, and the absolute between-day recovery (n=5) was 77-81%. The within-day precision (n=5) and between-day precision (n=5) were 2.59-5.82% and 3.17-4.55%, respectively. No interferences from endogenous substances were observed. Taken together, the above HPLC assay method by deproteinization and UV detection was suitable for the determination of LB71350 in the preclinical pharmacokinetics.

Administration, Oral↗

PubMed1997

High-performance liquid chromatographic assay of bromocriptine in plasma and eye tissue of the rabbit.

A reliable reversed-phase high-performance liquid chromatographic method has been developed for the determination of bromocriptine (BCT) in plasma and eye tissues. The BCT and propranolol, added as an internal standard (I.S.), were extracted by a liquid-liquid technique followed by an aqueous back-extraction, allowing injection of an aqueous solvent into a 4-microm Nova-Pak C18 column (150x3.9 mm I.D.). The mobile phase was a mixture of 30 parts of acetonitrile and 70 parts of 0.2% triethylamine (pH 3) at a flow-rate of 1 ml/min. Fluorescence detection was at an excitation wavelength of 330 nm and an emission wavelength of 405 nm. The retention times of I.S. and BCT were 4.1 and 11.6 min, respectively. The calibration curve was linear over the concentration range 0.2-10 microg/l for plasma (r>0.999) and vitreous humour (r>0.997) and 1-50 microg/l for aqueous humour (r>0.985). The limit of quantification was 0.2 microg/l for plasma and vitreous humour using a 1-ml sample and was 1 microg/l for aqueous humour using a 0.2-ml sample. The quality control samples were reproducible with acceptable accuracy and precision. The within-day recovery (n=3) was 100-102% for plasma, 91-106% for aqueous humour and 96-111% for vitreous humour. The between-day recovery (n=9) was 90-114% for plasma, 83-115% for aqueous humour and 90-105% for vitreous humour. The within-day precision (n=3) and the between-day precision (n=9) were 1.7-7.0% and 8.1-13.6%, respectively. No interferences from endogenous substances were observed. Taken together, the above simple, sensitive and reproducible high-performance liquid chromatography assay method was suitable for the determination of BCT in plasma and eye tissues following ocular application of BCT for the therapy of myopia.

Animals↗

PubMed1997

Isolation and characterization of the 54-kDa and 22-kDa chitinase genes of Serratia marcescens KCTC2172.

A DNA fragment (pCHI5422) containing two genes encoding a 54-kD and a 22-kDa chitinase was isolated from a cosmid DNA library of Serratia marcescens KCTC2172. The complete nucleotide sequence of pCHI5422 consisting of 4581 bp was determined. The nucleotide sequence of the 22-kDa chitinase consists of 681 bp of open reading frame encoding 227 amino acids and is located 1422 bp downstream of the translation termination codon of the 54-kDa chitinase sequence. The 54-kDa chitinase gene consisted of 1497 bp in a single open reading frame encoding 499 amino acids. The genes encoding the 54-kDa and 22-kDa chitinase were separately subcloned in Escherichia coli and the individual chitinases were expressed and purified from the culture broth using chitin affinity chromatography. When chitohexaose was used as substrate, the major product of the enzymatic reaction of both the 54-kDa and 22-kDa chitinases was a (GlcNAc)2 dimer with a minor amount of monomer. The specific activity of the 54-kDa and 22-kDa chitinases were 300 microM (min)-1 mg-1 and 17 microM (min)-1 mg-1 on the natural swollen chitin, respectively.

Amino Acid Sequence↗

PubMed1997

Construction of a Helicobacter pylori-Escherichia coli shuttle vector for gene transfer in Helicobacter pylori.

In this study, a Helicobacter pylori-Escherichia coli shuttle vector was constructed for transferring DNA into H. pylori. The smallest cryptic plasmid (1.2 kb), pHP489, among those harbored by 77 H. pylori isolates was selected as a base replicon for constructing vectors. HindIII-digested pHP489 was ligated with a kanamycin resistance gene [aph(3')-III], which originated from Campylobacter jejuni, to produce the recombinant plasmid pHP489K. pHP489K was efficiently transformed into and stably maintained in H. pylori strains. The shuttle vector pBHP489K (3.6 kb) was constructed by the recombination of pHP489, ColE1, and aph(3')-III sequences. pBHP489K was reciprocally transformed into and maintained in both H. pylori and E. coli. Introduction of the shuttle vector clone DNA (pBHP489K/AB; 6.7 kb), containing the ureA and ureB genes of H. pylori, into urease-negative mutants of H. pylori led to the restoration of their urease activity. The transformants were confirmed to contain the incoming plasmid DNA. pBHP489K satisfied the requirements for an H. pylori-E. coli shuttle vector, implying that it might be a useful vector for investigating pathogenicity and restriction-modification systems of H. pylori.

Cloning, Molecular↗

PubMed1997

Evaluation of acute renal failure in bacterial allograft pyelonephritis using abdominal CT and graft biopsy.

The causes of acute renal failure in bacterial allograft pyelonephritis were evaluated using abdominal CT and graft biopsy. Twenty-one recipients, who showed a poor response to antibiotic therapy, comprised this study group. The diagnostic approach taken with this poor responder group was first to perform abdominal CT. If a focal lesion was identified on abdominal CT, a diagnosis of acute focal bacterial nephritis or renal abscess was made. If no focal lesion was found, a graft biopsy was performed for diagnosis. Abdominal CT revealed focal lesions in 9 of the 21 recipients, and renal biopsy showed superimposed acute rejection in 8 of the 12 recipients biopsied. In conclusion, acute renal failure in allograft pyelonephritis is associated with not only severe infection but also a superimposed acute rejection process. Therefore, imaging study and graft biopsy are recommended in the poor responder group.

Acute Kidney Injury↗

PubMed1997

Compensatory growth in dairy heifers: the effect of a compensatory growth pattern on growth rate and lactation performance.

The objective of this study was to improve the efficiency of growth and lactation performance of dairy heifers fed for a stair-step growth pattern. Twenty-four young Holstein heifers were randomly assigned to either control or test groups. The test group was fed according to a schedule of 3, 2, 4, 2, 5 and 2 mo in which feed intake was alternately 20% below or 25% above requirements. Heifers that were subjected to the stair-step growth pattern gained more body weight and consumed less dry matter, resulting in improved efficiency of growth compared with that of controls (7.8% vs. 8.3%). First estrus, first conception, gestation period, services per conception, and calving difficulty (dystocia) were not affected by stair-step growth. Concentration of growth hormone in blood serum was elevated during feed restriction for the test heifers; however, during refeeding, growth hormone was decreased compared with that in the blood serum of control heifers. Mammary tissues obtained by biopsy from heifers in middle and late pregnancy were used for chemical composition analysis. Stair-step growth increased DNA, RNA, protein, the ratio of RNA to DNA, and the ratio of protein to DNA. Lipid decreased in the mammary tissue of test heifers in late pregnancy (9.5 mo). Heifers in the test group yielded approximately 9% more milk than did heifers in the control group. These results indicate that compensatory growth can contribute to the improvement of growth efficiency and lactation performance.

Animal Nutritional Physiological Phenomena↗