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S Park

Publications and source records attributed to S Park.

At least 181 records · Page 10Linked to original sources
PubMed2000

Reiterative transcription initiation from galP2 promoter of Escherichia coli.

The expression of gal operon in Escherichia coli is driven by two promoters, P1 and P2 separated by 5 bp. The transcription initiated from the P2 generates a large amount of abortive transcripts to produce a comparable amount of full-length transcript as P1 in vitro. In this study, we investigated the source of the abortive transcripts by employing a quantitative potassium permanganate footprinting method that determines the extent of open promoter complex formation. The extents of open promoter complex formation at the two gal promoters were about the same during the given reaction time while the amount of transcription initiation determined by in vitro transcription assay showed a considerable difference: several hundred-fold more transcription initiation from the P2 than the P1, most of which was abortive. Thus, it was concluded that the abortive transcripts are generated reiteratively by a small fraction of RNA polymerase. An in vitro transcription assay using an immobilized DNA template revealed that the fraction of RNA polymerase generating abortive transcripts never produces the full-length transcript and it remains bound to the promoter. We concluded that there are two kinds of RNA polymerase-promoter complexes formed at galP2, at least in vitro, productive complex and nonproductive complex; and, the nonproductive complex is responsible for generating large amount of abortive transcripts from the P2.

Carrier Proteins↗
PubMed2000

Immunoliposome sandwich assay for the detection of Escherichia coli O157:H7.

We describe the development of a field-portable colorimetric immunoassay for the detection of Escherichia coli O157:H7, using antibody-directed liposomes (immunoliposomes) encapsulating dye as an analytical reagent. Antibodies (anti-E. coli O157:H7) thiolated by 2-iminothiolane were coupled to malemide-tagged liposomes encapsulating the marker dye, sulforhodamine B. Transmission electron microscopy showed that the immunoliposomes bound only to the serotype without any cross-reactivity with tested negative controls. A wicking reagent containing immunoliposomes and the test sample and a plastic-backed nitrocellulose strip with a measurement zone were used in a sandwich (noncompetitive) assay format. During the capillary migration of the wicking reagent, E. coli, with surface-bound immunoliposomes, was captured at the measurement zone on which antibodies to E. coli O157:H7 were immobilized. The color density of the measurement zone was directly proportional to the amount of E. coli O157:H7 in the sample. The detection limit of the current assay with pure cultures of the serotype was ca. 10(4) colony-forming units (CFU)/mL. The assay, which does not need washing and incubation steps, can be completed in 8 min. These results demonstrate the feasibility of using dye-encapsulating immunoliposomes in microporous membranes for the rapid detection of molecules with multivalent antigenic sites.

Antibodies, Bacterial↗
PubMed2000

Direct oxidation of hydrocarbons in a solid-oxide fuel cell

The direct electrochemical oxidation of dry hydrocarbon fuels to generate electrical power has the potential to accelerate substantially the use of fuel cells in transportation and distributed-power applications. Most fuel-cell research has involved the use of hydrogen as the fuel, although the practical generation and storage of hydrogen remains an important technological hurdle. Methane has been successfully oxidized electrochemically, but the susceptibility to carbon formation from other hydrocarbons that may be present or poor power densities have prevented the application of this simple fuel in practical applications. Here we report the direct, electrochemical oxidation of various hydrocarbons (methane, ethane, 1-butene, n-butane and toluene) using a solid-oxide fuel cell at 973 and 1,073 K with a composite anode of copper and ceria (or samaria-doped ceria). We demonstrate that the final products of the oxidation are CO2 and water, and that reasonable power densities can be achieved. The observation that a solid-oxide fuel cell can be operated on dry hydrocarbons, including liquid fuels, without reforming, suggests that this type of fuel cell could provide an alternative to hydrogen-based fuel-cell technologies.

Journal Article↗
PubMed2000

WD40 repeat proteins striatin and S/G(2) nuclear autoantigen are members of a novel family of calmodulin-binding proteins that associate with protein phosphatase 2A.

Protein phosphatase 2A (PP2A) is a multifunctional serine/threonine phosphatase that is critical to many cellular processes including development, neuronal signaling, cell cycle regulation, and viral transformation. PP2A has been implicated in Ca(2+)-dependent signaling pathways, but how PP2A is targeted to these pathways is not understood. We have identified two calmodulin (CaM)-binding proteins that form stable complexes with the PP2A A/C heterodimer and may represent a novel family of PP2A B-type subunits. These two proteins, striatin and S/G(2) nuclear autoantigen (SG2NA), are highly related WD40 repeat proteins of previously unknown function and distinct subcellular localizations. Striatin has been reported to associate with the post-synaptic densities of neurons, whereas SG2NA has been reported to be a nuclear protein expressed primarily during the S and G(2) phases of the cell cycle. We show that SG2NA, like striatin, binds to CaM in a Ca(2+)-dependent manner. In addition to CaM and PP2A, several unidentified proteins stably associate with the striatin-PP2A and SG2NA-PP2A complexes. Thus, one mechanism of targeting and organizing PP2A with components of Ca(2+)-dependent signaling pathways may be through the molecular scaffolding proteins striatin and SG2NA.

3T3 Cells↗
PubMed2000

Calibration of the dietary questionnaire for a multiethnic cohort in Hawaii and Los Angeles.

The performance of the dietary questionnaire used in a multiethnic cohort study in Hawaii and Los Angeles was assessed in a calibration substudy that compared diet reported from the questionnaire with three 24-hour dietary recalls. For the calibration substudy, subjects from each of eight subgroups defined by sex and ethnic group (African-American, Japanese-American, Latino, and White) were chosen randomly from among the cohort members, and each participant's previous day's diet was assessed by telephone recall on three occasions over approximately 2 months. After completing the three 24-hour recalls, each calibration subject was sent a second questionnaire; 1,606 persons completed three recalls and a second questionnaire (127 to 267 per ethnic-sex group). This report describes correlation coefficients and calibration slopes for the relation between the 24-hour recalls and second questionnaire values for a selected set of macro- and micronutrients, as absolute intakes, nutrient densities, and calorie-adjusted nutrients. In all subgroups, estimates of the correlation between the questionnaire and 24-hour recalls were greater after energy adjustment (average correlations ranged from 0.57-0.74 for nutrient densities and from 0.55-0.74 for calorie-adjusted nutrients) than when absolute nutrient values were used (average range 0.26-0.57). For absolute nutrient intakes, the correlations were greatest for Whites, somewhat lower for Japanese-Americans and Latinos, and lowest for African-Americans. After energy adjustment, the difference between subgroups were diminished, and the correlations were generally highly satisfactory.

Black or African American↗
PubMed2000

Asp-99 donates a hydrogen bond not to Tyr-14 but to the steroid directly in the catalytic mechanism of Delta 5-3-ketosteroid isomerase from Pseudomonas putida biotype B.

Delta 5-3-ketosteroid isomerase (KSI) catalyzes the allylic isomerization of Delta 5-3-ketosteroids at a rate approaching the diffusion limit by an intramolecular transfer of a proton. Despite the extensive studies on the catalytic mechanism, it still remains controversial whether the catalytic residue Asp-99 donates a hydrogen bond to the steroid or to Tyr-14. To clarify the role of Asp-99 in the catalysis, two single mutants of D99E and D99L and three double mutants of Y14F/D99E, Y14F/D99N, and Y14F/D99L have been prepared by site-directed mutagenesis. The D99E mutant whose side chain at position 99 is longer by an additional methylene group exhibits nearly the same kcat as the wild-type while the D99L mutant exhibits ca. 125-fold lower kcat than that of the wild-type. The mutations made at positions 14 and 99 exert synergistic or partially additive effect on kcat in the double mutants, which is inconsistent with the mechanism based on the hydrogen-bonded catalytic dyad, Asp-99 COOH...Tyr-14 OH...C3-O of the steroid. The crystal structure of D99E/D38N complexed with equilenin, an intermediate analogue, at 1.9 A resolution reveals that the distance between Tyr-14 O eta and Glu-99 O epsilon is ca. 4.2 A, which is beyond the range for a hydrogen bond, and that the distance between Glu-99 O epsilon and C3-O of the steroid is maintained to be ca. 2.4 A, short enough for a hydrogen bond to be formed. Taken together, these results strongly support the idea that Asp-99 contributes to the catalysis by donating a hydrogen bond directly to the intermediate.

Asparagine↗
PubMed2000

Novel mechanism of massive photoreceptor degeneration caused by mutations in the trp gene of Drosophila.

The Drosophila trp gene encodes a light-activated Ca(2+) channel subunit, which is a prototypical member of a novel class of channel proteins. Previously identified trp mutants are all recessive, loss-of-function mutants characterized by a transient receptor potential and the total or near-total loss of functional TRP protein. Although retinal degeneration does occur in these mutants, it is relatively mild and slow in onset. We report herein a new mutant, Trp(P365), that does not display the transient receptor potential phenotype and is characterized by a substantial level of the TRP protein and rapid, semi-dominant degeneration of photoreceptors. We show that, in spite of its unusual phenotypes, Trp(P365) is a trp allele because a Trp(P365) transgene induces the mutant phenotype in a wild-type background, and a wild-type trp transgene in a Trp(P365) background suppresses the mutant phenotype. Moreover, amino acid alterations that could cause the Trp(P365) phenotype are found in the transmembrane segment region of the mutant channel protein. Whole-cell recordings clarified the mechanism underlying the retinal degeneration by showing that the TRP channels of Trp(P365) are constitutively active. Although several genes, when mutated, have been shown to cause retinal degeneration in Drosophila, the underlying mechanism has not been identified for any of them. The present studies provide evidence for a specific mechanism for massive degeneration of photoreceptors in Drosophila. Insofar as some human homologs of TRP are highly expressed in the brain, a similar mechanism could be a major contributor to degenerative disorders of the brain.

Amino Acid Sequence↗
PubMed2000

Surface modification of poly(ethylene terephthalate) angioplasty balloons with a hydrophilic poly(acrylamide-co-ethylene glycol) interpenetrating polymer network coating.

An interpenetrating polymer network (IPN) of poly(acrylamide-co-ethylene glycol) (p(AAm-co-EG)) hydrogel was covalently grafted to polyethylene terephthalate (PET) angioplasty balloons to increase surface hydrophilicity and improve lubricity. A 2-step graft polymerization protocol was followed to first polymerize and cross-link acrylamide onto the substrate with a photosensitizer and/or oxygen plasma pretreatment. The effects of varying photo-initiation and plasma exposure times were investigated separately and conjunctively using water contact angles to obtain optimal coating deposition parameters. A poly(ethylene glycol) network was then grafted by swelling the preexisting polyacrylamide network to allow inter-diffusion of the monomer and cross-linker, which were then polymerized by photo-initiation. When the photo-initiation time was long enough to reach near gelation, pretreatment of PET with oxygen plasma did not offer significant benefit. X-ray photoelectron spectroscopy confirmed the presence of both polymer layers, and composition depth profiles supported the assessment that an interpenetrating network was formed. Tensile testing and application of Weibull statistics on unmodified and modified films indicated that the surface modification approach did not significantly alter the mechanical integrity of the material. These findings indicate that a p(AAm-co-EG) coating can be effectively deposited on PET surfaces without compromising the structural integrity of the substrate.

Acrylic Resins↗
PubMed2000

Optimized production and purification of Bacillus anthracis lethal factor.

Bacillus anthracis lethal factor (LF) is a 90-kDa zinc metalloprotease that plays an important role in the virulence of the organism. LF has previously been purified from Escherichia coli and Bacillus anthracis. The yields and purities of these preparations were inadequate for crystal structure determination. In this study, the genes encoding wild-type LF and a mutated, inactive LF (LF-E687C) were placed in an E. coli-Bacillus shuttle vector so that LF was produced with the protective antigen (PA) signal peptide at its N-terminus. The resulting vectors, pSJ115 and pSJ121, express wild-type and mutated LF fusion proteins, respectively. Expression of the LF genes is under the control of the PA promoter and, during secretion, the PA signal peptide is cleaved to release the 90-kDa LF proteins. The wild-type and mutated LF proteins were purified from the culture medium using three chromatographic steps (Phenyl-Sepharose, Q-Sepharose, and hydroxyapatite). The purified proteins were greater than 95% pure and yields (20-30 mg/L) were higher than those obtained in other expression systems (1-5 mg/L). These proteins have been crystallized and are being used to solve the crystal structure of LF. Their potential use in anthrax vaccines is also discussed.

Amino Acid Substitution↗
PubMed2000

Reduction of peritonitis with the rectus abdominis muscle flap in a CAPD patient.

An adolescent maintained on continuous ambulatory peritoneal dialysis (CAPD) for 8 years had relapsing peritonitis involving peritoneal catheter tunnel infections. We attempted catheter removal and replacement simultaneously, with the catheter covered cylindrically by a rectus abdominis muscle flap to prevent recurrent tunnel infections. During 3 years of follow-up, there have been no episodes of peritonitis involving tunnel infection. Our modified insertion technique can eradicate tunnel infection, thus reducing peritonitis.

Adolescent↗
PubMed2000

Development of screening systems for drugs against human papillomavirus-associated cervical cancer: based on E6-E6AP binding.

Human papillomavirus (HPV) E6 protein forms a ternary complex with the cell-cycle regulator p53 and the E6-associated protein (E6AP) known as an E3 ubiquitin protein ligase, leading to the degradation of p53 via the ubiquitination pathway. As an attempt to employ interaction between HPV viral oncogene E6 and a cellular protein E6AP for in vitro screening system of drugs against HPV infection, we primarily investigated the E6AP-E6 binding through pull down assay and enzyme-linked immunosorbent assay (ELISA). E6AP immobilized on the resin produced specifically complexes with bacterially expressed E6 in a dose-dependent manner, as determined by immunoblot analysis. This result was collinear with that shown in ELISA, which is a useful system for mass-screening potential drugs with rapidity and cheapness. Screening system based on the interaction between E6AP and E6 may be a promising system in the development of drugs against cervical cancer caused by HPV infection.

Blotting, Western↗
PubMed2000

Modulation of attentional inhibition by norepinephrine and cortisol after psychological stress.

Two of the most salient physiological responses to stress are increased norepinephrine (NE) and cortisol (CORT) activities. However, it is unclear how these neurochemical events affect cognition, especially attention. We examined the effects of mild psychological stress on selective attention, as assessed by the negative priming (NP) paradigm. Salivary measures of the stress hormone CORT and alpha-amylase (a correlate of NE) were assayed to probe the relationship between the stress response and attentional inhibition. Healthy subjects (N = 20) engaged in the attention task, which was then followed by 15 min of a stressful video game before a return to the attentional task. Baseline saliva samples were obtained before the experiment began, 1 min after the video-game stressor, and 20 min post-stress. Subjects showed a significant reduction in NP and a decrease in reaction time (RT) after the video game. Moreover, alpha-amylase levels increased significantly after the stressor, indicating the role of NE in the acute stress response. While CORT levels remained unchanged after stress, CORT correlated significantly with both NP scores and RT after the stressor. These results imply that mild psychological stress can significantly alter attentional processes. Given the increase in alpha-amylase and the correlation between attention and CORT after stress, it seems likely that attentional processes are under tight control by brain systems which mediate the fight-or-flight response.

Adolescent↗
PubMed2000

Nicotine impairs spatial working memory while leaving spatial attention intact.

We investigated the effects of nicotine on spatial working memory and spatial selective attention in young, healthy smokers. Spatial working memory was assessed by a delayed response task. Delayed response performance is associated with the integrity of the dorsolateral prefrontal cortex. Spatial interference and negative priming tasks were used to assess spatial selective attention. Nicotine impaired spatial working memory in smokers but it did not affect spatial selective attention. This result suggests that nicotine may impair dorsolateral prefrontal function, as assessed by the spatial working memory task in young smokers and that this deficit does not stem from impairments in spatial selective attention. However, the effects of nicotine on working memory and selective attention in nonsmokers or in psychiatric population with suspected nicotinic receptor abnormalities (e.g., schizophrenia patients) cannot be deduced from the present study.

Adult↗
PubMed2000

Myelodysplasias and leukemias after autologous stem cell transplantation for lymphoid malignancies.

The incidence of secondary myelodysplastic syndromes and acute leukemia (MDS/AL) was reported for 395 patients autografted for Hodgkin's disease (HD) (n = 96) and non-Hodgkin's lymphoma (NHL) (n = 299) between 1987 and 1998. Eleven patients developed secondary MDS/AL (crude rate at 2.8%) including two lymphoblastic AL cases. The mean time of occurrence was at 32 months after autologous stem cell transplantation (ASCT) and 71 months after diagnosis. The estimated actuarial incidence at 10 years was at 6.3% (+/-4%). Karyotyping revealed complex chromosomal aberrations in only one patient, and two translocations [t(8;21) and t(8;16)]. No features of topoisomerase II inhibitor-related leukemia were found. Only one patient had received ASCT in first remission. The remaining 10 patients had received multiple courses of chemotherapy before stem cell collection and four had relapsed after ASCT and before the occurrence of secondary MDS/AL. Five of 11 patients had received localized radiotherapy and five others received TBI in their conditioning regimen. Ten patients died despite chemotherapy and/or supportive care and only one patient is alive and well after genoidentical allogeneic transplantation. We suggest a cumulative leukemogenic role of pre-ASCT radiation and chemotherapy in the occurrence of these secondary MDS/AL more than the high-dose therapy itself.

Acute Disease↗
PubMed2000

The role of IL-12 in inflammatory activity of patients with rheumatoid arthritis (RA).

The aim of this study was to investigate the role of IL-12 in patients with RA. IL-12 (p70) and its associated cytokines were measured in sera and synovial fluid (SF) using an enzyme-linked immunosorbent method. Seven American College of Rheumatology (ACR) core set measures as well as IL-12 levels were sequentially monitored at the commencement and 4 months after treatment with a low-dose steroid and disease-modifying anti-rheumatic drugs (DMARDs). In sera, 64 (42.2%) of 152 RA patients had detectable concentrations of IL-12 (p70), whereas one (1.4%) of 69 osteoarthritis (OA) patients and five (10%) of 50 healthy controls had detectable IL-12 (P < 0.001). The median level of circulating IL-12 was also higher in RA patients (P < 0.001). In SF, the number of patients with detectable IL-12 and the median IL-12 levels were significantly higher in RA patients (n = 53) than in OA patients (n = 22). In paired samples (n = 53) of sera and SF from RA patients, IL-12 levels were higher in the SF than in sera (P < 0.001). Patients with detectable IL-12 (n = 51) in sera had higher tender joint scores (P = 0.003), swollen joint scores (P < 0.001) and C-reactive protein (CRP; P = 0.036), than those without (n = 55). Four months after treatment with DMARDs, the improved group showed a larger IL-12 decrease than the non-improved group (P = 0.017). The levels of IL-12 correlated positively with those of IL-2, interferon-gamma, IL-6, and tumour necrosis factor-alpha, but were correlated inversely with those of IL-10. Our results demonstrate that IL-12 levels reflect RA disease activity and that IL-12 is involved in the production of proinflammatory cytokines. An IL-12 blockade could be useful for the treatment of RA.

Adult↗
PubMed2000

Identification of myelinated motor and sensory axons in a regenerating mixed nerve.

The common peroneal nerves of Wistar rats were transected and repaired to compare the sequential changes in the numbers of regenerating motor and sensory myelinated axons in a single mixed nerve. At sequential intervals (2, 4, and 12 weeks) after nerve repair, 3 kinds of staining were performed: cholinesterase staining (Karnovsky's staining) for motor axons, carbonic anhydrase staining for sensory axons, and antineurofilament immunohistochemical staining for all axons. At 2 weeks there was a large number of carbonic anhydrase-positive axons (600 +/- 98; mean +/- SD) and cholinesterase-positive axons were occasionally seen. Subsequently, there was a striking increase of cholinesterase-positive myelinated axons, reaching to 302 +/- 50 at 12 weeks. The results suggest that the myelinated sensory axons regenerate faster in the early stage of nerve regeneration and that regeneration of the myelinated motor axons is prominent in the subsequent stage. (J Hand Surg 2000; 25A:104-111.

Acetylcholinesterase↗
PubMed2000

Mutagenicity of recombinant antihemophilic factor (GC-gamma AHF).

This study was carried out to evaluate the mutagenic potential of recombinant antihemophilic factor VIII (GC-gamma AHF). Salmonella typhimurium (S. typhimurium) reversion assay with/without histidine moiety, chromosomal aberration assay on Chinese hamster lung (CHL) fibroblast cells and in vivo micronucleus assay using mouse bone marrow cells and supravital micronucleus assay using peripheral blood were performed. GC-gamma AHF containing histidine did show inconsistent and irregular mutagenic effects on S. typhimurium TA98, TA100, TA1535 and TA1537 both in the absence and presence of the metabolic activation system, however, GC-gamma AHF without histidine showed no mutagenic effects regardless of the metabolic activation system, thus suggesting that the histidine moiety in GC-gamma AHF might cause inconsistent mutagenic effect. Also GC-gamma AHF did not increase the number of cells having structural or numerical chromosome aberration in the cytogenetic test. In classical and supravital micronucleus assay, no significant increases were observed in the occurrence of micronucleated polychromatic erythrocytes and micronucleated peripheral lymphocytes in male ICR mice. These results strongly indicate that GC-gamma AHF has no genetic toxicity under these experimental conditions.

Animals↗