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S Choi

Publications and source records attributed to S Choi.

At least 73 records · Page 4Linked to original sources
PubMed2001

Search for heavy particles decaying into electron-positron pairs in pp collisions.

We present results of searches for technirho (rho(T)), techniomega (omega(T)), and Z' particles, using the decay channels rho(T),omega(T),Z'-->e(+)e(-). The search is based on 124.8 pb(-1) of data collected by the D0 detector at the Fermilab Tevatron during 1992-1996. In the absence of a signal, we set 95% C.L. upper limits on the cross sections for the processes pp-->rho(T),omega(T),Z'-->e(+)e(-) as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate rho(T) and omega(T) states with masses below about 200 GeV. We exclude a Z' with mass below 670 GeV, assuming that it has the same couplings to fermions as the Z boson.

Journal Article↗
PubMed2001

Spectrometric evidence for the flavin-1-phenylcyclopropylamine inactivator adduct with monoamine oxidase N.

1-Phenylcyclopropylamine (1-PCPA) is shown to be an inactivator of the fungal flavoenzyme monoamine oxidase (MAO) N. Inactivation results in an increase in absorbance at 410 nm and is accompanied by the concomitant loss of the flavin absorption band at 458 nm. The spectral properties of the covalent adduct formed between the flavin cofactor of MAO N and 1-PCPA are similar to those reported for the irreversible inactivation product formed with 1-PCPA and mammalian mitochondrial monoamine oxidase B [Silverman, R. B., and Zieske, P. A. (1985) Biochemistry 24, 2128-2138]. There is a hypsochromic shift of the 410 nm band upon lowering the pH to 2, indicating that an N(5)-flavin adduct formed upon inactivation. Use of the fungal enzyme, MAO N, which lacks the covalent attachment to the flavin adenine dinucleotide (FAD) cofactor present in the mammalian forms MAO A and MAO B, has allowed for the isolation and further structural identification of the flavin-inactivator adduct. The incorporation of two (13)C labels into the inactivator, [2,3-(13)C(2)]-1-PCPA, followed by analysis using on-line liquid chromatography/electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy, provided a means to explore the structure of the flavin-inactivator adduct of MAO N. The spectral evidence supports covalent attachment of the 1-PCPA inactivator to the cofactor as N(5)-3-oxo-3-phenylpropyl-FAD.

Aspergillus niger↗
PubMed2001

Quasi-model-independent search for new high p(T) physics at D0.

We apply a quasi-model-independent strategy ("Sleuth") to search for new high p(T) physics in approximately 100 pb(-1) of pp collisions at square root of (s) = 1.8 TeV collected by the D0 experiment during 1992-1996 at the Fermilab Tevatron. We systematically analyze many exclusive final states and demonstrate sensitivity to a variety of models predicting new phenomena at the electroweak scale. No evidence of new high p(T) physics is observed.

Journal Article↗
PubMed2001

Inhibition of nicotinic acetylcholine receptors and calcium channels by clozapine in bovine adrenal chromaffin cells.

The effects of clozapine on the activities of nicotinic acetylcholine receptors (nAChRs) and voltage-sensitive calcium channels (VSCCs) were investigated and compared with those of chlorpromazine (CPZ) in bovine adrenal chromaffin cells. [(3)H]Norepinephrine ([(3)H]NE) secretion induced by activation of nAChRs was inhibited by clozapine and CPZ with half-maximal inhibitory concentrations (IC(50)) of 10.4 +/- 1.1 and 3.9 +/- 0.2 microM, respectively. Both cytosolic calcium increase and inward current in the absence of extracellular calcium induced by nicotinic stimulation were also inhibited by clozapine and CPZ, but the greater inhibition was achieved by CPZ. In addition, [(3)H]nicotine binding to chromaffin cells was inhibited by clozapine and CPZ with IC(50) values of approximately 19 and 2 microM, respectively. On the other hand, [(3)H]NE secretion induced by high K(+) was inhibited by clozapine and CPZ with similar IC(50) values of 15.5 +/- 3.8 and 17.1 +/- 3.9 microM, respectively. Our results suggest that clozapine, as well as CPZ, inhibits nAChRs and VSCCs, thereby causing inhibition of catecholamine secretion, and that clozapine is much less potent than CPZ in inhibiting nAChRs.

Adrenal Glands↗
PubMed2001

Immunogenicity of the E1E2 proteins of hepatitis C virus expressed by recombinant adenoviruses.

The E1 and E2 proteins of hepatitis C virus (HCV) are believed to be the viral envelope glycoproteins that are major candidate antigens for HCV vaccine development. We reported previously that the replication-competent recombinant adenovirus encoding core-E1-E2 genes of HCV (Ad/HCV) produces serologically reactive E1 and E2 proteins forming a heterodimer in substantial amounts. Here, we examined immunogenicity of the E1E2 proteins copurified from HeLa cells infected with Ad/HCV virus in mice. Furthermore, we constructed a replication-defective recombinant adenovirus encoding the core-E1-E2 genes of HCV (Ad.CMV.HCV) and examined immunogenicity of the virus in mice. The mice immunized intraperitoneally with the copurified E1E2 proteins induced mainly antibodies to E2, but not to E1 by Western blot analysis. The sera of mice immunized with the E1E2 inhibited the binding of E2 protein to the major extracellular loop of human CD81. E2-specific cytotoxic T cells (CTLs), but not antibodies to the E1E2 antigens were induced in the mice intramuscularly immunized with Ad.CMV.HCV virus. When immunized with both Ad.CMV.HCV virus and the E1E2, mice elicited E2-specific CTLs and antibodies to the E1E2 antigens. The results suggest that immunization of Ad.CMV.HCV virus combined with E2 protein is an effective modality to induce humoral as well as cellular immune response to E2 antigen.

Adenoviridae↗
PubMed2001

Polarization measurements in high-energy deuteron photodisintegration.

We present measurements of the recoil proton polarization for the d(gamma-->,p-->)n reaction at straight theta(c.m.) = 90 degrees for photon energies up to 2.4 GeV. These are the first data in this reaction for polarization transfer with circularly polarized photons. The induced polarization p(y) vanishes above 1 GeV, contrary to meson-baryon model expectations, in which resonances lead to large polarizations. However, the polarization transfer Cx does not vanish above 1 GeV, inconsistent with hadron helicity conservation. Thus, we show that the scaling behavior observed in the d(gamma,p)n cross sections is not a result of perturbative QCD. These data should provide important tests of new nonperturbative calculations in the intermediate energy regime.

Journal Article↗
PubMed2001

Ratio of jet cross sections at square root of s = 630 GeV and 1800 GeV.

The D0 Collaboration has measured the inclusive jet cross section in barpp collisions at square root of s = 630 GeV. The results for pseudorapidities (eta)<0.5 are combined with our previous results at square root of s = 1800 GeV to form a ratio of cross sections with smaller uncertainties than either individual measurement. Next-to-leading-order QCD predictions show excellent agreement with the measurement at 630 GeV; agreement is also satisfactory for the ratio. Specifically, despite a 10% to 15% difference in the absolute magnitude, the dependence of the ratio on jet transverse momentum is very similar for data and theory.

Journal Article↗
PubMed2001

Ratios of multijet Cross Sections in p p collisions at radical(s) = 1.8 TeV.

We report on a study of the ratio of inclusive three-jet to inclusive two-jet production cross sections as a function of total transverse energy in p&pmacr; collisions at a center-of-mass energy sqrt[s] = 1.8 TeV, using data collected with the D0 detector during the 1992-1993 run of the Fermilab Tevatron Collider. The measurements are used to deduce preferred renormalization scales in perturbative O(alpha(3)(s)) QCD calculations in modeling soft-jet emission.

Journal Article↗
PubMed2001

Inclusive jet production in pp(macro) collisions.

We report a new measurement of the pseudorapidity (eta) and transverse-energy ( E(T)) dependence of the inclusive jet production cross section in pp(macro) collisions at square root of s = 1.8 TeV using 95 pb(-1) of data collected with the D0 detector at the Fermilab Tevatron. The differential cross section d(2)sigma/(dE(T)d eta) is presented up to eta = 3, significantly extending previous measurements. The results are in good overall agreement with next-to-leading order predictions from QCD and indicate a preference for certain parton distribution functions.

Journal Article↗
PubMed2001

Search for large extra dimensions in dielectron and diphoton production.

We report a search for effects of large extra spatial dimensions in pp collisions at a center-of-mass energy of 1.8 TeV with the D0 detector, using events containing a pair of electrons or photons. The data are in good agreement with the expected background and do not exhibit evidence for large extra dimensions. We set the most restrictive lower limits to date, at the 95% C.L. on the effective Planck scale between 1.0 and 1.4 TeV for several formalisms and numbers of extra dimensions.

Journal Article↗
PubMed2001

Prmt5, which forms distinct homo-oligomers, is a member of the protein-arginine methyltransferase family.

We found that JBP1, known as a human homolog (Skb1Hs) of Skb1 of fission yeast, interacts with NS3 of the hepatitis C virus in a yeast two-hybrid screen. Amino acid sequence analysis revealed that Skb1Hs/JBP1 contains conserved motifs of S-adenosyl-l-methionine-dependent protein-arginine methyltransferases (PRMTs). Here, we demonstrate that Skb1Hs/JBP1, named PRMT5, is a distinct member of the PRMT family. Recombinant PRMT5 protein purified from human cells methylated myelin basic protein, histone, and the amino terminus of fibrillarin fused to glutathione S-transferase. Myelin basic protein methylated by PRMT5 contained monomethylated and dimethylated arginine residues. Recombinant glutathione S-transferase-PRMT5 protein expressed in Escherichia coli also contained the catalytic activity. Sedimentation analysis of purified PRMT5 on a sucrose density gradient indicated that PRMT5 formed distinct homo-oligomeric complexes, including a dimer and tetramer, that comigrated with the enzyme activity. The PRMT5 homo-oligomers were dissociated into a monomer in the presence of a reducing agent, whereas a monomer, dimer, and multimer were detected in the absence or at low concentrations of a reducing agent. The results indicate that both covalent linkage by a disulfide bond and noncovalent association are involved in the formation of PRMT5 homo-oligomers. Western blot analysis of sedimentation fractions suggests that endogenous PRMT5 is present as a homo-oligomer in a 293T cell extract. PRMT5 appears to have lower specific enzyme activity than PRMT1. Although PRMT1 is known to be mainly located in the nucleus, human PRMT5 is predominantly localized in the cytoplasm.

Amino Acid Sequence↗
PubMed2001

Doppler sonography of the penile cavernosal artery: comparison of intraurethral instillation and intracorporeal injection of prostaglandin E1.

PURPOSE: We compared the Doppler sonographic findings in the penile cavernosal artery (arteria profunda penis) after intraurethral instillation and intracorporeal injection of prostaglandin E1 (PGE1) to evaluate the hemodynamic changes during drug-induced erection. METHODS: Twenty healthy male volunteers were enrolled in the study. Ten subjects (intraurethral group) were examined with Doppler sonography of the penile cavernosal artery after intraurethral administration of 1 mg of PGE1. The remaining 10 subjects (intracorporeal group) underwent Doppler sonography of the cavernosal artery after intracorporeal injection of 5 microg of PGE1. The peak systolic velocity, minimal diastolic velocity, and resistance index were determined at 5-minute intervals for 30 minutes following administration of PGE1 in both groups. The results were compared between the 2 groups. RESULTS: The peak systolic velocity in the intraurethral group increased progressively from a mean of 31.1 cm/second at 5 minutes to 65.6 cm/second at 30 minutes after intraurethral administration of PGE1. In the intracorporeal group, the mean peak systolic velocity ranged from 44.1 to 83.2 cm/second, reached a maximum at 10 minutes, and then decreased continuously through 30 minutes after intracorporeal injection of PGE1. The mean peak systolic velocities were significantly higher in the intracorporeal group at 10 and 15 minutes (p < or = 0.05); the mean minimal diastolic velocities were significantly lower in the intracorporeal group at 15, 20, and 25 minutes (p < or = 0.05); and the mean resistance indices were significantly higher in the intracorporeal group at all time points except 5 minutes (p < or = 0.05). CONCLUSIONS: The intracorporeal injection of PGE1 produced a greater vasoactive response in the cavernosal artery than did intraurethral instillation.

Adult↗
PubMed2001

Obesity is associated with reduced self-rated general health status: evidence from a representative sample of white, black, and Hispanic Americans.

BACKGROUND: Although the evidence linking obesity with many chronic diseases is well established, the relationship with self-rated health is not clear. Self-rating of health is a broad summary measure of different domains of health that include psychosocial domain. The aims of this study were to examine the relationship between obesity and self-rated health and the degree of agreement between patients' self-rated health status and physicians' impression of patients' health in a representative sample of healthy noninstitutionalized American adults. METHODS: Data (n = 10, 298) used for this analysis were obtained from the Third National Health and Nutrition Examination Survey. Normal weight was defined as BMI 18.5-24.9 kg/m(2) and preobesity was defined as BMI 25-29.9 kg/m(2). Moderate (class I) obesity was defined as BMI 30-34.9 kg/m(2) and severe (class II) obesity as BMI > or =35 kg/m(2). Self-rated health conditions were categorized as excellent, very good, good, fair, or poor. Agreement between physicians' impression and self-rated health and a linear relationship between obesity and individual perceived health were quantified using kappa and gamma statistics, respectively. Using the logistic regression analysis, odds of reporting reduced health in preobese, class I obese, and class II obese individuals were compared with those for normal-weight individuals, adjusting for age, current smoking, and alcohol intake. The contribution of obesity to ethnic differences in reduced self-rated health was determined by comparing blacks with whites and Hispanics with whites fitted in multiple logistic regression models. RESULTS: Among both men and women, there was a statistically significant linear association between obesity and self-rated health (P < 0.05). The proportion of subjects reporting excellent health tended to decrease with increasing level of obesity in the three ethnic groups. In the three ethnic groups, the degrees of concordance between self-rated health and physicians' impressions were poor and decreased with increasing obesity level. In each ethnic group, class II obesity was associated with approximately twofold increased odds of reporting reduced health compared with normal-weight individuals. Compared to whites, black and Hispanic races/ethnicities were respectively associated with 23 and 175% increased odds of reduced self-rated health among men. The corresponding values for women were 45 and 177%, respectively. CONCLUSION: The results of this study provide evidence that obesity has a negative impact on self-rated health among adults, even in the absence of chronic disease conditions. The results of this investigation also underscore the need to craft national preventive strategies to curb obesity in these at-risk population groups.

Black or African American↗
PubMed2001

Synthesis and in vitro antibacterial activity of cephalosporins with a pyridinium substituent carrying an isoxazole moiety at the C-3 position.

Several quaternary pyridinium cephalosporin analogues were prepared and evaluated in vitro for antibacterial activity against selected gram-positive and gram-negative organisms. Most of the synthesized analogues were either as effective or less effective against the tested bacterial organisms than the reference compounds, Cefpirome and Ceftazidime.

Cephalosporins↗
PubMed2001

Effect of ginsenosides on voltage-dependent Ca(2+) channel subtypes in bovine chromaffin cells.

In previous reports we have shown that ginsenosides inhibit high threshold voltage-dependent Ca(2+) channels in neuronal cells. However, these studies did not show whether ginsenosides-induced inhibition of Ca(2+) currents discriminates among the various Ca(2+) channel subtypes, although it is known that there are at least five different Ca(2+) channel subtypes in neuronal cells. In this study we investigated the effect of ginsenosides on high threshold voltage-dependent Ca(2+) channel subtypes using their selective Ca(2+) channel blockers nimodipine (L-type), omega-conotoxin GVIA (N-type), or omega-agatoxin IVA (P-type) in bovine chromaffin cells. We could observe that ginsenosides inhibited high threshold voltage-dependent Ca(2+) currents in a dose-dependent manner. The IC(50) was about 120 microgram/ml. Nimodipine had no effect on ginsenosides response. However, the effect of ginsenosides on Ca(2+) currents was reduced by omega-conotoxin GVIA, omega-agatoxin IVA, and mixture of nimodipine, omega-conotoxin GVIA, and omega-agatoxin IVA. These data suggest that ginsenosides are negatively coupled to three types of calcium channels in bovine chromaffin cell, including an omega-conotoxin GVIA-sensitive (N-type) channel, an omega-agatoxin IVA-sensitive (P-type) channel and nimodipine/omega-conotoxin GVIA/omega-agatoxin VIA-resistant (presumptive Q-type) channel. Thus, the selective regulation of voltage-dependent Ca(2+) subtypes by ginsenosides in bovine chromaffin cell could be the cellular basis of antistress effects induced by ginseng.

Animals↗
PubMed2001

Is (re)titration of nasal continuous positive airway pressure for obstructive sleep apnoea necessary?

OBJECTIVE: To assess changes in nasal continuous positive airway pressure (nCPAP) pressure requirements across time in obstructive sleep apnoea (OSA), and whether routine retitrations are indicated. BACKGROUND: Most sleep laboratories perform one nCPAP titration, although some authors have found changes in pressures with time. A cohort of patients with OSA in a randomised controlled trial of nCPAP provided us with data on changes in titration pressures with time. METHODS: One hundred and one patients with symptomatic OSA (Epworth Sleepiness Scale > or =10, and >10 episodes/h of >4% dips in SaO(2) overnight) were recruited to a 1 month trial comparing real (autotitrated) and placebo nCPAP. At 1 month all patients were titrated and received real nCPAP thereafter. Eighty five were retitrated at about 6 months. RESULTS: Average pressures did not change between the initial value and 1 month (95th centile, 8.47 (SD 3.00), 8.94 (2.85) cm H(2)O), although there were large individual changes (mean difference, +0.47, SD 2.30, range -5 to +6 cm H(2)O). There was a small fall at 6 months (mean difference -0.68, SD 2.60, range -6 to +6 cm H(2)O, P<0.03) with no suggestion that the changes from 1-6 months were clinically important. CONCLUSIONS: This study suggests that routine nCPAP retitrations are not necessary. In conjunction with other published data, the night to night variation we found implies that a nCPAP calibration using an algorithm (based on obesity and OSA severity) might be as clinically successful as conventional one night titrations. However, further studies will be needed to specifically confirm this hypothesis.

Clinical Trial↗
PubMed2001

Hypertension and type 2 diabetes comorbidity in adults in the United States: risk of overall and regional adiposity.

OBJECTIVE: To evaluate the impact of generalized, abdominal, and truncal fat deposits on the risk of hypertension and/or diabetes and to determine whether ethnic differences in these fat patterns are independently associated with increased risk for the hypertension-diabetes comorbidity (HDC). RESEARCH METHODS AND PROCEDURES: Data (n = 7075) from the Third U.S. National Health and Nutrition Examination Survey were used for this investigation. To assess risks of hypertension and/or diabetes that were due to different fat patterns, odds ratios of men and women with various cut-points of adiposities were compared with normal subjects in logistic regression models, adjusting for age, smoking, and alcohol intake. To evaluate the contribution of ethnic differences in obesity to the risks of HDC, we compared blacks and Hispanics with whites. RESULTS: Generalized and abdominal obesities were independently associated with increased risk of hypertension, diabetes and HDC in white, black, and Hispanic men and women. The risk of HDC due to generalized, truncal, and abdominal obesities tended to be higher in whites than blacks and Hispanics. In men, the contribution of black and Hispanic ethnicities to the increased risk of HDC due to the various obesity phenotypes was approximately 73% and approximately 61%, respectively. The corresponding values for black and Hispanic women were approximately 115% and approximately 125%, respectively. CONCLUSIONS: In addition to advocating behavioral lifestyles to curb the epidemic of obesity among at-risk populations in the United States, there is also the need for primary health care practitioners to craft their advice to the degree and type of obesity in these at-risk groups.

Adipose Tissue↗