Biomedical subjects

J K Choi

Publications and source records attributed to J K Choi.

At least 73 records · Page 4Linked to original sources

PubMed1996

A modified Coomassie blue staining of proteins in polyacrylamide gels with Bismark brown R.

A rapid and sensitive protein staining method employing a mixed dye technique has been developed. Solutions of Coomassie brilliant blue R-250 (CB, 0.2%) and Bismark brown R (BBR, 0.05%) were mixed in the volume ratio of 1:0.75 for staining (final molar ratio, 4.5:1). In this staining, BBR inhibits the binding of CB to gel matrix by forming ion-pairing complex with excess CB; therefore, it reduces staining/destaining times and also enhances the staining effect of CB on protein band. As a result, the mixed dye staining enables complete staining/destaining within 20/25 min and detection of up to 25 ng of bovine serum albumin.

Animals↗

PubMed1996

Thermal balance of man in water: prediction of deep body temperature change.

Changes in rectal temperature and metabolic rate were continuously monitored in men immersed in water at 15, 20, 25, 30, and 35 degrees C. The subjects (12 healthy male students) wore swimming suits while either resting or doing leg exercise (delta M approximately 60 kcal.h-1.m-2 approximately 70 W.m-2) for 1 h. At all water temperatures below 30 degrees C, the metabolic rate increased but the rectal temperature fell continuously, resulting in hypothermia. The rate of fall in rectal temperature (cooling rate, CR, degrees C.h-1) was inversely proportional to water temperature (Tw, degrees C) according to the equation CR = 3.818-0.109 Tw in resting subjects and CR = 3.434-0.110 Tw in exercising subjects. At a given Tw the cooling rate was greater in resting than in exercising subjects and in lean than in obese subjects. From the relationships between the cooling rate and water temperature the duration of useful activity and the survival time were predicted for resting and exercising subjects of various fatness.

Adult↗

PubMed1995

Modular structural elements in the replication origin region of Tetrahymena rDNA.

Computer analyses of the DNA replication origin region in the amplified rRNA genes of Tetrahymena thermophila identified a potential initiation zone in the 5'NTS [Dobbs, Shaiu and Benbow (1994), Nucleic Acids Res. 22, 2479-2489]. This region consists of a putative DNA unwinding element (DUE) aligned with predicted bent DNA segments, nuclear matrix or scaffold associated region (MAR/SAR) consensus sequences, and other common modular sequence elements previously shown to be clustered in eukaryotic chromosomal origin regions. In this study, two mung bean nuclease-hypersensitive sites in super-coiled plasmid DNA were localized within the major DUE-like element predicted by thermodynamic analyses. Three restriction fragments of the 5'NTS region predicted to contain bent DNA segments exhibited anomalous migration characteristic of bent DNA during electrophoresis on polyacrylamide gels. Restriction fragments containing the 5'NTS region bound Tetrahymena nuclear matrices in an in vitro binding assay, consistent with an association of the replication origin region with the nuclear matrix in vivo. The direct demonstration in a protozoan origin region of elements previously identified in Drosophila, chick and mammalian origin regions suggests that clusters of modular structural elements may be a conserved feature of eukaryotic chromosomal origins of replication.

Animals↗

PubMed1995

Increasing intracellular concentrations of thymosin beta 4 in PtK2 cells: effects on stress fibers, cytokinesis, and cell spreading.

Thymosin beta 4 (T beta 4) binds to G-actin in vitro and inhibits actin polymerization. We studied the effects of increasing T beta 4 concentration within living PtK2 cells, comparing its effects on the disassembly of stress fibers and membrane-associated actin with its ability to inhibit cytokinesis and cell spreading after mitosis. We chose PtK2 cells for the study because these cells have many striking actin bundles in both stress fibers and cleavage furrows. They also have prominent concentrations of membrane-associated actin and remain flattened during mitosis. We have found that PtK2 cells contain an endogenous homologue of T beta 4 at a concentration (approximately 28 microM) sufficient to complex a third or more of the cell's unpolymerized actin. Intracellular T beta 4 concentrations were increased by three different methods: 1) microinjection of an RSV vector containing a cDNA for T beta 4; 2) transfection with the same vector; and 3) microinjection of purified T beta 4 protein. The plasmid coding for T beta 4 was microinjected into PtK2 cells together with fluorescently labeled alpha-actinin as a reporter molecule. Immediately after microinjection fluorescently labeled alpha-actinin was detected in a periodic pattern along the stress fibers just as in control cells injected solely with the reporter. However, after 13 h, cells microinjected with reporter and plasmid showed marked disassembly of the fiber bundles. PtK2 cells transfected with this RSV vector for 2-3 days showed disassembly of stress fibers as detected by rhodamine-phalloidin staining; in these cells the membrane actin was also greatly diminished or absent and the border of the cells was markedly retracted. Microinjection of pure T beta 4 protein into interphase PtK2 cells induced disassembly of the stress fibers within 10 min, while membrane actin appeared only somewhat reduced. If the PtK2 cells were mitotic, similar microinjection of pure thymosin beta 4 protein at times from early prophase to metaphase resulted in an unusual pattern of delayed cytokinesis. Furrowing occurred but at a much slower rate than in controls and the amount of actin in the cleavage furrow was greatly reduced. The cells constricted to apparent completion, but after about 30 min the furrow regressed, forming a binucleate cell, much as after treatment with cytochalasin B or D. Postcytokinesis spreading of these T beta 4-injected cells was often inhibited. These experiments suggest that an insufficient number of actin filaments prolongs the contractile phase of cytokinesis and abolishes the final sealing process.

Actinin↗

PubMed1995

Cloning of the 3'-terminal region encoding movement and coat proteins of a Korean isolate of odontoglossum ringspot virus.

The 3'-terminal 1855 nucleotides (nts) of a Korean isolate of odontoglossum ringspot tobamovirus (ORSV-Cy) were cloned and sequenced. The sequence contained two open reading frames, which encode the cell-to-cell movement protein (MP) and coat protein genes, and are 912 nts and 477 nts long, respectively. The MP gene contained a conserved sequence motif of tobamoviruses and putative assembly origin of the viral RNA locating between 1117 nts and 1292 nts from the 3'-end. The 3' untranslated region (UTR) of the virus comprises 414 nts, includes nine pseudoknots and a tRNA-like structure domain containing aminoacyl acceptor arm and the anticodon hairpin loop coding for histidine.

Amino Acid Sequence↗

PubMed1995

Molecular cloning and characterization of the cDNA coding for the biotin-containing subunit of the chloroplastic acetyl-coenzyme A carboxylase.

We report the molecular cloning and sequence of the cDNA coding for the biotin-containing subunit of the chloroplastic acetylcoenzyme A (CoA) carboxylase (ACCase) of Arabidopsis thaliana (CAC1). The 3' end of the CAC1 sequence, coding for a peptide of 94 amino acids, which includes a putative biotinylation motif, was expressed in Escherichia coli as a glutathione-S-transferase (GST) fusion protein. The resulting GST-CAC1 fusion protein was biotinylated in vivo, indicating that CAC1 codes for a biotin-containing protein. Antibodies generated to the GST-CAC1 protein reacted solely with the 38-kD biotin-containing polypeptide of Arabidopsis. Furthermore, these antibodies inhibited ACCase activity in extracts from Arabidopsis leaves. The deduced amino acid sequence of CAC1 has an apparent N-terminal chloroplast-targeting transit peptide. The CAC1 protein is coded by a single Arabidopsis gene, and its mRNA accumulates to the highest levels in organs that are undergoing rapid growth. The amino acid sequence of the CAC1 protein is most similar to the biotin carboxyl-carrier protein component of eubacterial ACCases. These characterizations identify CAC1 as the biotin-containing subunit of the plastidic, heteromeric ACCase of Arabidopsis. The results support the ancient origin of the two structurally distinct ACCases of plants.

Acetyl-CoA Carboxylase↗

PubMed1994

Ontogeny of protein kinase C in the rat hippocampus: an autoradiographic study with [3H]phorbol 12,13-dibutyrate.

The ontogeny of protein kinase C (PKC) in the hippocampus was studied in 1-week-, 4-week-, and 3-month-old Wistar rats with in vitro receptor autoradiography using [3H]phorbol 12,13-dibutyrate ([3H]PDBu). The developmental pattern of [3H]PDBu binding varied within hippocampal subregions. [3H]PDBu binding in stratum oriens of the CA1 and CA3 sectors and stratum lucidum of the CA3 sector increased to adult levels by 4 weeks. In strata moleculare and granulosum of the dentate gyrus, the binding reached peak values at 4 weeks but declined at 3 months. Interestingly, in stratum lacunosum-moleculare of the CA1 sector, the [3H]PDBu binding activity was the highest at 1 week. There were constant binding activities in stratum radiatum of the CA1 and CA3 sectors and the dentate hilus during the postnatal development. These findings may provide evidence that PKC has a distinct role in different subregions of the hippocampus during postnatal development.

Animals↗

PubMed1993

Inhibition of human immunodeficiency virus-1 protease by a C2-symmetric phosphinate. Synthesis and crystallographic analysis.

The human immunodeficiency virus type 1 (HIV-1) protease is a potential target of acquired immune deficiency syndrome (AIDS) therapy. A highly potent, perfectly symmetrical phosphinate inhibitor of this enzyme, SB204144, has been synthesized. It is a competitive inhibitor of HIV-1 protease, with an apparent inhibition constant of 2.8 nM at pH 6.0. The three-dimensional structure of SB204144 bound to the enzyme has been determined at 2.3-A resolution by X-ray diffraction techniques and refined to a crystallographic discrepancy factor, R (= sigma parallel F(o) magnitude to - Fc parallel/sigma magnitude of F(o)), of 0.178. The inhibitor is held in the enzyme active site by a set of hydrophobic and hydrophilic interactions, including an interaction between Arg8 and the center of the terminal benzene rings of the inhibitor. The phosphinate establishes a novel interaction with the two catalytic aspartates; each oxygen of the central phosphinic acid moiety interacts with a single oxygen of one aspartic acid, establishing a very short (2.2-2.4 A) oxygen-oxygen contact. As with the structures of penicillopepsin bound to phosphinate and phosphonate inhibitors [Fraser, M. E., Strynadka, N. C., Bartlett, P. A., Hanson, J. E., & James, M. N. (1992) Biochemistry 31, 5201-14], we interpret this short distance and the stereochemical environment of each pair of oxygens in terms of a hydrogen bond that has a symmetric single-well potential energy curve with the proton located midway between the two atoms.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1993

Detection of proteins on polyacrylamide gels using calconcarboxylic acid.

We describe here a protein staining method in polyacrylamide gels with a new staining dye, 1-(2-hydroxy-4-sulfo-1-naphthylazo)-2-hydroxy-3-naphthoic acid (calconcarboxylic acid, NN). This method can be performed by both simultaneous and postelectrophoretic staining techniques. Simultaneous staining using 0.01% of NN in upper reservoir buffer eliminates the poststaining step, and thus enables detection of the proteins more rapidly and simply. In poststaining, proteins can be stained by a 30-min incubation of a polyacrylamide gel in 40% methanol/7% acetic acid solution of 0.05% NN. These techniques produced protein staining patterns identical to the ones obtained by the conventional poststaining with Coomassie blue R-250 (CB). NN staining can detect as little as 10 ng of bovine serum albumin by poststaining and 25 ng by simultaneous staining, compared to 50 ng detectable by CB poststaining. In comparing the relationship between band intensity and amount of protein, NN staining gave better linearity than CB staining.

Azo Compounds↗

PubMed1993

Renal response to head-out water immersion in Korean women divers.

Head-out water immersion (HOI) induces a profound diuresis and natriuresis, which may endanger the body fluid balance of breath-hold divers during prolonged diving work. To investigate if adaptation is acquired by professional breath-hold divers, we have evaluated renal responses to 3-h HOI in 5 Korean women divers (Amas) and 11 nondiving housewives (controls). In both control and diver groups, the average urine flow during 3-h immersion was four times greater and Na+ excretion was 70%-80% greater than the pre-immersion value [urine flow: 3.7 (SD 1.0) ml.min-1 vs 0.9 (SD 0.4), P < 0.001, in controls; 4.3 (SD 0.9) vs 1.1 (SD 0.4), P < 0.001, in divers; Na+ excretion: 270 (SD 176) mumol.min-1 vs 161 (SD 84), P < 0.025, in controls; 303 (SD 31) vs 164 (SD 62), P < 0.005, in divers]. In all cases, the values for a given period were not significantly different between the two groups. The plasma concentrations of Na+ and osmolality, and renal clearance of creatinine did not change significantly. However, the osmolal clearance increased [from 2.0 (SD 0.8) ml.min-1 to 2.8 (SD 0.7), P < 0.05, in the controls; from 2.2 (SD 0.4) to 2.6 (SD 0.4), P < 0.05, in the divers] and free water clearance changed from negative to positive values [from -1.1 (SD 0.5) ml.min-1 to 1.2 (SD 0.3), P < 0.005, in the controls; from -1.2 (SD 0.4) to 1.6 (SD 1.1), P < 0.01, in the divers] during immersion, again the pattern of change being similar in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

G-actin pool and actin messenger RNA during development of the apical processes of the retinal pigment epithelial cells of the chick.

It has been suggested that during development an increase in the pool of G-actin may drive the elongation of actin-containing processes which occur in several types of epithelial cells. The apical processes of chick retinal pigment epithelial (RPE) cells elongate during the last 7 days of embryonic life (E15-E21) reaching lengths of 20 microns or more by hatching (E21). F-actin bundles form the cores of these processes. We followed the elongation by measuring F-actin in the cells and cytoskeletons. In correlation with this, we studied by DNAse assay the levels of monomeric actin in supernatants of cell extracts from E13, before elongation starts, to E17, when elongation is well underway. Total F-actin increased 1.9-fold over this time period and cytoskeletal actin increased 2.5-fold. In supernatants from extracts of E13 RPE the monomeric actin concentration was 51 +/- 0.5 micrograms/ml. From estimates of cell volume we calculated the cellular monomeric actin concentration at E13 as at least 510 micrograms/ml (13 microM). We compared this with monomeric actin levels in extracts from RPE at E15 and E17. Allowing for the estimated increase in cell volume, our data show little overall change in cellular monomeric actin concentration at these times. Changes in the level of actin mRNA were measured over the same time period. Normalized to equal RNA, we found a twofold increase in beta actin mRNA and a four- to fivefold increase in message for gamma actin at E17 as compared to E13. In summary, we show that (1) there is a substantial pool of monomeric actin in these epithelial cells before elongation starts; (2) process elongation is not associated with a significant change in the size of this pool; and (3) process elongation is associated with a significant increase in actin mRNA.

Actins↗

PubMed1992

Effect of dehydration on thirst and drinking during immersion in men.

The mechanism for reduced voluntary water intake during water immersion was studied in eight men (19-25 yr of age) immersed to the neck while sitting for 3 h at 34.5 degrees C or in air at 28 degrees C when euhydrated (Eu-H2O and Eu-air, respectively) and hypohydrated (Hypo-H2O and Hypo-air) by 3.6% body weight loss. Thirst sensations (degree of thirst, mouth dryness and taste, drinking desirability, and stomach fullness) were similar at the beginning of Hypo-air and Hypo-H2O test periods. Initial drinking of tap water (15 degrees C) was 216 +/- 30 ml/7 min (P less than 0.05) with Hypo-air, decreased to 108 +/- 28 ml/7 min (P less than 0.05) with Hypo-H2O, and was 10-50 ml/10-30 min thereafter. Intake was less than 10 ml/10-30 min in Eu-air, and there was no drinking in Eu-H2O. Within the first 10 min of immersion, compared with Hypo-air findings, the significant reduction in drinking in the Hypo-H2O experiment was associated with unchanged plasma Na+, plasma osmolality, heart rates, and mean arterial pressures; the different responses were increased cardiac output, plasma volume, and atrial natriuretic peptides and decreased plasma renin activity and arginine vasopressin. Thus the extracellular pathway, as opposed to the osmotic pathway, appears to be the major mechanism for immersion-induced suppression of drinking.

Adult↗

PubMed1992

Increase of heat loss by wearing gloves and boots in wet-suited subjects working in cold water.

The effect of wearing protective gloves and boots on thermal exchanges of wet-suited subjects in cold water was evaluated. Four male subjects, clad in 5 mm-thick neoprene wet suits and either with or without neoprene gloves (5 mm-thick) and boots (5 mm-thick) were immersed up to the neck in water at 13 degrees C while resting for 3 h or exercising for 2 h. Rectal temperature, oxygen consumption and local (chest, back, upper arm, thigh, forearm, calf, hand and foot) skin temperatures, skin heat fluxes and thermal insulations were determined during immersion. The rectal temperature was not different between conditions but the skin temperature was significantly higher with gloves and boots, especially at the distal extremities (forearm, calf, hand and foot). Consequently, the core-to-skin temperature gradient was reduced by wearing gloves and boots, but the skin heat loss was markedly increased. Calculated overall body insulation was significantly lowered by wearing gloves and boots. These results indicate that in wet-suited subjects resting or exercising in cold (13 degrees C) water, gloves and boots increase the overall rate of body heat loss. Attenuation of cold-induced vasoconstriction is proposed as the mechanism.

Adult↗

PubMed1991

Phorbol esters selectively and reversibly inhibit a subset of myofibrillar genes responsible for the ongoing differentiation program of chick skeletal myotubes.

Phorbol esters selectively and reversibly disassemble the contractile apparatus of cultured skeletal muscle as well as inhibit the synthesis of many contractile proteins without inhibiting that of housekeeping proteins. We now demonstrate that phorbol esters reversibly decrease the mRNA levels of at least six myofibrillar genes: myosin heavy chain, myosin light chain 1/3, myosin light chain 2, cardiac and skeletal alpha-actin, and skeletal troponin T. The steady-state message levels decrease 50- to 100-fold after 48 h of exposure to phorbol esters. These decreases can be attributed at least in part to decreases in transcription rates. For at least two genes, cardiac and skeletal alpha-actin, some of the decreases are the result of increased mRNA turnover. In contrast, the cardiac troponin T steady-state message level does not change, and its transcription rate decreases only transiently upon exposure to phorbol esters. Phorbol esters do not decrease the expression of the housekeeping genes, alpha-tubulin, beta-actin, and gamma-actin. Phorbol esters do not decrease the steady-state message levels of MyoD1, a gene known to be important in the activation of many skeletal muscle-specific genes. Cycloheximide blocks the phorbol ester-induced decreases in transcription, message stability, and the resulting steady-state message level but does not block the tetradecanoyl phorbol acetate-induced rapid disassembly of the I-Z-I complexes. These results suggests a common mechanism for the regulation of many myofibrillar genes independent of MyoD1 mRNA levels, independent of housekeeping genes, but dependent on protein synthesis.

Animals↗

PubMed1990

Spectral perturbations and oligomer/monomer formation in 124-kilodalton Avena phytochrome.

We have studied the effects of pH, ionic strength, and hydrophobic fluorescence probes, 8-anilinonaphthalene-1-sulfonate (ANS) and bis-ANS, on the structure of intact (124-kDa) Avena phytochrome. The Pfr form of phytochrome forms oligomers in solution to a greater extent than the Pr form. Hydrophobic forces play a major role in the oligomerization of phytochrome, as suggested by fluorescence and monomerization by bis-ANS. However, electrostatic charges also take part in the phytochrome oligomerization. The partial proteolytic digestion patterns for the Pr and Pfr species are different, but binding of bis-ANS to the phytochrome abolishes this difference and yields an identical proteolytic peptide mapping for both spectral forms of phytochrome. This appears to result from bis-ANS binding at the carboxy-terminal domain, which induces monomerization of phytochrome oligomers. A second bis-ANS binding at an amino-terminal site blocks cleavage sites of trypsin and alpha-chymotrypsin. Bis-ANS especially blocks access of the proteases to the amino-terminal cleavage site that produces an early proteolytic product (114/118 kDa) on SDS gels. The bis-ANS binding does not, however, affect the proteolytic cleavage site that occurs in the hinge region between the two structural domains of phytochrome, the chromophore domain and the C-terminal non-chromophore domain. A chromophore binding site in the Pfr form is apparently exposed for preferential binding of bis-ANS, causing cyclization of the chromophore and bleaching of its absorbance at 730 nm. These observations have been discussed in terms of a photoreversible topographic change of the chromophore/apoprotein during the phototransformation of phytochrome.

Anilino Naphthalenesulfonates↗

PubMed1989

Purified maturation promoting factor phosphorylates pp60c-src at the sites phosphorylated during fibroblast mitosis.

We have previously shown that overexpressed chicken pp60c-src has retarded mobility, novel serine/threonine phosphorylation, and enhanced kinase activity during NIH 3T3 cell mitosis. Here we show that novel mitotic phosphorylations occur at Thr 34, Thr 46, and Ser 72. The possibility, previously raised, that Ser 17 is dephosphorylated during mitosis is excluded. The phosphorylated sites lie in consensus sequences for phosphorylation by p34cdc2, the catalytic component of maturation promoting factor (MPF). Furthermore, highly purified MPF from metaphase-arrested Xenopus eggs phosphorylated both wild-type and kinase-defective pp60c-src at these sites. Altered phosphorylation alone is sufficient to account for the large retardation in mitotic pp60c-src electrophoretic mobility: phosphorylation of normal pp60c-src by MPF retarded mobility and dephosphorylation of mitotic pp60c-src restored normal mobility. These results suggest that pp60c-src is one of the targets for MPF action, which may account in part for the pleiotropic changes in protein phosphorylation and cellular architecture that occur during mitosis.

Amino Acid Sequence↗

PubMed1989

Mutation of amino acids in pp60c-src that are phosphorylated by protein kinases C and A.

The product of the c-src proto-oncogene, pp60c-src, is phosphorylated at Ser-17 by cyclic AMP-dependent protein kinase A and at Ser-12 by calcium-phospholipid-dependent protein kinase C (when stimulated by 12-O-tetradecanoyl phorbol acetate). We tested the effects of Ser----Ala and Ser----Glu mutations at these sites in pp60c-src and in pp60c-src(F527) (a mutant whose transforming activities are enhanced by Tyr-527----Phe mutation) by transfecting single-, double-, and triple-mutant src expression plasmids into NIH 3T3 cells. Tryptic phosphopeptide analyses of the mutant proteins confirmed prior biochemical identifications of the phosphorylation sites and showed that neither separate nor coordinate mutations at Ser-12 and Ser-17 affected Tyr-416, Tyr-527, or Ser-48 phosphorylation or prevented mitosis-specific phosphorylations of either pp60c-src or pp60c-src(F527). Ser-12 mutation did not affect phosphorylation of the Ser-17-containing peptide, but mutation of Ser-17 significantly increased phosphorylation at Ser-12. Specific kinase activities (both with and without in vivo 12-O-tetradecanoyl phorbol acetate treatment) and the abilities of pp60c-src and pp60c-src(F527) to induce foci, transformed morphologies, and anchorage-independent growth were unaffected by any of the serine mutations. Thus, pp60c-src transforming activity in NIH 3T3 cells is relatively insensitive to phosphorylation at these sites, but there is a suggestion that Ser-17 phosphorylation may have a subtle regulatory effect.

Amino Acids↗

PubMed1989

[Case report of the Sturge-Weber syndrome with intraoral finding].

The authors observed a 20-year-old female patient who had come to Department of Dentistry, Kyungpook National University Hospital due to the chief complaints of gingival enlargement and pain on the upper jaw. We performed the clinical, hematologic and radiologic examinations for the patient and obtained the following results; 1. We observed a nevus flammeus on the right side of the facial area, soft palate and buccal mucosa. 2. The enlargement of the upper and lower gingiva, we thought, was due to inflammatory reaction. 3. The above clinical signs were found in accordance with the maxillary and ophthalmic branch of trigeminal nerve. 4. The maxillary sinus was enlarged in Water's view. 5. Finally, we have reached the diagnosis of Sturge-Weber syndrome for the patient.

Adult↗