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Biomedical subjects

K Lee

Publications and source records attributed to K Lee.

At least 271 records · Page 15Linked to original sources
PubMed2000

Aerobic activity of Escherichia coli alcohol dehydrogenase is determined by a single amino acid.

Expression of the alcohol dehydrogenase gene, adhE, in Escherichia coli is anaerobically regulated at both the transcriptional and the translational levels. To study the AdhE protein, the adhE(+) structural gene was cloned into expression vectors under the control of the lacZ and trp(c) promoters. Wild-type AdhE protein produced under aerobic conditions from these constructs was inactive. Constitutive mutants (adhC) that produced high levels of AdhE under both aerobic and anaerobic conditions were previously isolated. When only the adhE structural gene from one of the adhC mutants was cloned into expression vectors, highly functional AdhE protein was isolated under both aerobic and anaerobic conditions. Sequence analysis revealed that the adhE gene from the adhC mutant contained two mutations resulting in two amino acid substitutions, Ala267Thr and Glu568Lys. Thus, adhC strains contain a promoter mutation and two mutations in the structural gene. The mutant structural gene from adhC strains was designated adhE*. Fragment exchange experiments revealed that the substitution responsible for aerobic expression in the adhE* clones is Glu568Lys. Genetic selection and site-directed mutagenesis experiments showed that virtually any amino acid substitution for Glu568 produced AdhE that was active under both aerobic and anaerobic conditions. These findings suggest that adhE expression is also regulated posttranslationally and that strict regulation of alcohol dehydrogenase activity in E. coli is physiologically significant.

Aerobiosis↗
PubMed2000

Substrate specificity of naphthalene dioxygenase: effect of specific amino acids at the active site of the enzyme.

The three-component naphthalene dioxygenase (NDO) enzyme system carries out the first step in the aerobic degradation of naphthalene by Pseudomonas sp. strain NCIB 9816-4. The three-dimensional structure of NDO revealed that several of the amino acids at the active site of the oxygenase are hydrophobic, which is consistent with the enzyme's preference for aromatic hydrocarbon substrates. Although NDO catalyzes cis-dihydroxylation of a wide range of substrates, it is highly regio- and enantioselective. Site-directed mutagenesis was used to determine the contributions of several active-site residues to these aspects of catalysis. Amino acid substitutions at Asn-201, Phe-202, Val-260, Trp-316, Thr-351, Trp-358, and Met-366 had little or no effect on product formation with naphthalene or biphenyl as substrates and had slight but significant effects on product formation from phenanthrene. Amino acid substitutions at Phe-352 resulted in the formation of cis-naphthalene dihydrodiol with altered stereochemistry [92 to 96% (+)-1R,2S], compared to the enantiomerically pure [>99% (+)-1R,2S] product formed by the wild-type enzyme. Substitutions at position 352 changed the site of oxidation of biphenyl and phenanthrene. Substitution of alanine for Asp-362, a ligand to the active-site iron, resulted in a completely inactive enzyme.

Amino Acid Substitution↗
PubMed2000

Characterization and targeted disruption of murine Nup50, a p27(Kip1)-interacting component of the nuclear pore complex.

p27(Kip1) is a member of the Cip-Kip family of cyclin-dependent kinase (Cdk) inhibitors that binds to cyclin-Cdk complexes and inhibits their catalytic activity in response to antiproliferative stimuli. p27(Kip1) is regulated by several posttranscriptional mechanisms, including subcellular localization. We have identified a component of the nuclear pore complex (NPC), termed Nup50, through its two-hybrid interactions with p27(Kip1). Nup50 is a nucleoplasmically oriented component of the nuclear pore complex with a role in protein export (T. Guan, R. H. Kehlenbach, E. C. Schirmer, A. Kehlenbach, F. Fan, B. E. Clurman, N. Arnheim, and L. Gerace, Mol. Cell. Biol. 20:5619-5630, 2000). We found that murine Nup50 is a widely expressed nucleoporin and that Nup50 expression is highest in the developing neural tube and adult testes. We have also examined interactions between Nup50 and the NPC and found specific two-hybrid interactions between Nup50 and several well-defined components of the NPC, as well as coimmunoprecipitation of Nup50 with the nucleoporin Nup153 from transfected mammalian cells. In order to study Nup50 function in vivo, we cloned the mouse Nup50 genomic locus and created a targeted Nup50 deletion in the mouse germ line. Nup50 disruption resulted in a complex phenotype characterized by late embryonic lethality, neural tube defects, and intrauterine growth retardation. Although Nup50-null mouse embryo fibroblasts exhibited no defects in either cell cycle control or p27(Kip1) regulation, Nup50 deletion was associated with abnormalities in p27(Kip1) expression and cell proliferation in the developing neuroepithelium. We conclude that Nup50 is a nucleoporin with essential functions during mouse development.

Amino Acid Sequence↗
PubMed2000

Hepatoportal bumetanide-sensitive K(+)-sensor mechanism controls urinary K(+) excretion.

To determine whether a K(+)-sensor mechanism exists in the hepatoportal region, periarterial hepatic afferent nerve activity responses to intraportal injection of KCl were examined in anesthetized rats. Hepatic afferent nerve activity increased in response to intraportal injection in a K(+) concentration-dependent manner, and the increase was attenuated by inhibition of the Na(+)-K(+)-2Cl(-) cotransporter by bumetanide in a dose-dependent manner. These results suggest that a bumetanide-sensitive K(+)-sensor mechanism exists in the hepatoportal region. Stimulation of this mechanism by intraportal KCl infusion elicited an immediate and powerful kaliuresis with no significant change in the plasma K(+) concentration; this was significantly greater than the kaliuresis induced by intravenous KCl infusion and was attenuated by severing the periarterial hepatic nervous plexus. These results indicate that a hepatoportal bumetanide-sensitive K(+)-sensor mechanism senses the portal venous K(+) concentration and that stimulation of this sensor mechanism causes kaliuresis, which is mainly mediated by the periarterial hepatic nervous plexus.

Afferent Pathways↗
PubMed2000

sucker encodes a zebrafish Endothelin-1 required for ventral pharyngeal arch development.

Mutation of sucker (suc) disrupts development of the lower jaw and other ventral cartilages in pharyngeal segments of the zebrafish head. Our sequencing, cosegregation and rescue results indicate that suc encodes an Endothelin-1 (Et-1). Like mouse and chick Et-1, suc/et-1 is expressed in a central core of arch paraxial mesoderm and in arch epithelia, both surface ectoderm and pharyngeal endoderm, but not in skeletogenic neural crest. Long before chondrogenesis, suc/et-1 mutant embryos have severe defects in ventral arch neural crest expression of dHAND, dlx2, msxE, gsc, dlx3 and EphA3 in the anterior arches. Dorsal expression patterns are unaffected. Later in development, suc/et-1 mutant embryos display defects in mesodermal and endodermal tissues of the pharynx. Ventral premyogenic condensations fail to express myoD, which correlates with a ventral muscle defect. Further, expression of shh in endoderm of the first pharyngeal pouch fails to extend as far laterally as in wild types. We use mosaic analyses to show that suc/et-1 functions nonautonomously in neural crest cells, and is thus required in the environment of postmigratory neural crest cells to specify ventral arch fates. Our mosaic analyses further show that suc/et-1 nonautonomously functions in mesendoderm for ventral arch muscle formation. Collectively our results support a model for dorsoventral patterning of the gnathostome pharyngeal arches in which Et-1 in the environment of the postmigratory cranial neural crest specifies the lower jaw and other ventral arch fates.

Amino Acid Sequence↗
PubMed2000

The prediction of adverse pregnancy outcome using low unconjugated estriol in the second trimester of pregnancy without risk of Down's syndrome.

To investigate the relationship between low unconjugated estriol (uE3) levels in the second trimester and adverse perinatal outcomes in pregnancies without increased risk for Down's syndrome, 1,096 women under 35 years of age underwent a mid-trimester AFP-hCG-uE3 screening test between January 1995 and June 1998. Multiple pregnancies, maternal diabetes, smoking and elevation of AFP and hCG levels more than 2.0 multiple of median (MoM) were excluded from our study population. The results were divided into a low-uE3 group with uE3 levels at or below 0.75 MoM and a normal uE3 group with uE3 levels above 0.75 MoM. The risk for adverse pregnancy outcome was compared between the two groups and the role of low uE3 as a predictor of adverse pregnancy outcome was determined. The data were assessed using chi 2 or Fisher exact test and then logistic regression was used for the final analysis. The odds ratio (OR) and corresponding 95% confidence intervals (CI) were also calculated. Unconjugated E3 levels at or below 0.75 MoM was significantly associated with fetal growth restriction after adjustment for maternal age, weight, sampling weeks, AFP and hCG levels (OR 0.413, 95% CI 0.174-0.900; P = 0.035). Low uE3 levels in the second-trimester could help in the detection of fetal growth restriction by a low risk group in Down's syndrome. Careful gestational dating and serial clinical and sonographic assessment of fetal growth may be required for the clinician to manage these parturients.

Adult↗
PubMed2000

Emerging antimicrobial resistance, plasmid profile and pulsed-field gel electrophoresis pattern of the endonuclease-digested genomic DNA of Neisseria gonorrhoeae.

Resistant gonococci are very prevalent in many countries, particularly in Asia. This study was conducted to determine the trend of resistance, the effect of decreasing the ciprofloxacin susceptibilities of gonococci on the prevalence of penicillinase-producing N. gonorrhoeae (PPNG), and to compare the epidemiology of strains with the previous studies. A total of 602 strains of gonococci were isolated from prostitutes in 1997-1999. Antimicrobial susceptibility was tested by NCCLS disk diffusion and agar dilution methods. For epidemiologic analysis, plasmid analysis and pulsed-field gel electrophoresis (PFGE) were performed. The proportion of PPNG remained high (79%), and the strains with decreased susceptibility to ciprofloxacin increased significantly from 67% in 1997 to 84% in 1999. Compared to our previous study, the PFGE patterns were similar, while the proportion of strain with the 3.2-MDa plasmid markedly decreased. In conclusion, a rapid increase in ciprofloxacin-nonsusceptible strains may suggest difficulties in the treatment of gonococcal infections in the near future with the drug. The recent decrease of PPNG with the 3.2-MDa plasmid may suggest that there is an epidemiological change in gonococcal infections, and the prevalence of related PFGE patterns suggests the dissemination of a few clones among the high risk populations.

DNA↗
PubMed2000

Korean Nationwide Surveillance of Antimicrobial Resistance of Bacteria in 1998.

Antimicrobial resistance surveillance can provide information needed for empirical therapy of antimicrobial agents and for control of resistance. To determine the trend of antimicrobial resistance in Korea, in vitro susceptibility data in 1998 were collected from 25 hospitals participating to a program of Korean Nationwide Surveillance of Antimicrobial Resistance (KONSAR). The data were analyzed based upon hospital location and bed capacity. The results showed that cefoxitin-resistant E. coli and K. pneumoniae and 3rd-generation cephalosporin-resistant K. pneumoniae were prevalent, that 3rd-generation cephalosporin-resistant E. cloacae, S. marcesens and A. baumannii had increased, and ampicillin-resistant S. enterica were not rare. Oxacillin-resistant S. aureus, penicillin-non-susceptible pneumococci and beta-lactamase-producing H. influenzae were prevalent even smaller hospitals surveyed, and an increase of imipenem-resistant P. aeruginosa and vancomycin-resistant E. faecium is a new obvious threat. In general, resistance rates to some old antimicrobial agents, i.e., E. coli to ampicillin and S. aureus to oxacillin were high and did not vary greatly between the different levels of hospitals, while the rates to some of the newer ones, i.e., P. aeruginosa to imipenem, was quite variable and depended on the hospitals, probably reflecting difference in selective pressure.

Ampicillin↗
PubMed2000

The effect of exposure to a commercial 2,4-D herbicide formulation during gestation on urethan-induced lung adenoma formation in CD-1 mice.

Female CD-1 mice were exposed to a commercial amine formulation of 2,4-dichlorophenoxyacetic acid (2,4-D) on days 6-16 of gestation in drinking water at concentrations ranging from 0 to 1.0% of the formulated product, equivalent to approximately 0-650 mg/kg/d expressed as the amine derivative. The effect of 2,4-D on urethan-induced pulmonary adenoma formation was evaluated in female offspring 19 w after birth. Urethan-induced sleeping times observed following ip injection of 1.5 mg urethan/g bw 7 w after birth were not altered by 2,4-D (p = 0.10), indicating that 2,4-D did not affect the rate of urethan elimination. 2,4-D exposure did not affect the number of tumors produced (p = 0.58), but did reduce the mean tumor diameter in the highest dose group (p < 0.01). This minor antineoplastic activity of 2,4-D may be related, in part, to inhibitory effects of 2,4-D on various enzymatic or metabolic pathways, essential for cellular growth and tissue development. Since exposure to 2,4-D during pregnancy had little impact of tumor production, it is unlikely that persistent alteration to developing immune cells involved in the cell-mediated immunosurveillance mechanisms occurred. The subtle alteration in tumor size and the mild impairment of growth in the offspring were observed almost exclusively in the highest treatment group. Since this level of exposure is well in excess of those associated with normal application of 2,4-D, the hazard to non-target mammalian populations appears minimal.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2000

Effects of gender on the autonomic modulation of the cardiovascular responses to lower body negative pressure.

BACKGROUND: The cardiovascular responses to submaximal lower body negative pressure (LBNP) appear to differ between genders, but the underlying mechanisms are uncertain. HYPOTHESIS: These differences are due to differences in the autonomic modulation of the cardiovascular system. METHODS: There were 14 women and 13 men who underwent LBNP to -50 mmHg in 10 mmHg increments of 6 min each. Heart rate (HR), stroke volume (SV), BP, forearm blood flow and R-R interval data were acquired. Spectral analysis of the R-R interval data was used to assess autonomic modulation with the low frequency component (LF) set at 0.04 to 0.15 Hz and the high frequency component (HF) at 0.15 to 0.4 Hz. RESULTS: The responses to LBNP to -40 mmHg did not differ between groups. LBNP of -50 mmHg evoked greater HR increases in the women than the men (7.2 +/- 1.0 vs. 3.8 +/- 1.1 bpm; p < 0.05), while SV, cardiac output and total peripheral conductance decreased more (-15 +/- 2 vs. -8 +/- 2 ml x beat(-1); -0.668 +/- 0.131 vs. -0.1778 +/- 0.124 L x min(-1); -0.009 +/- 0.002 vs. -0.004 +/- 0.001 units; p < 0.05). Normalized HF, an indicator of the vagal influence on HR variability, declined below rest at -40 mmHg while the LF/HF ratio, an indicator of sympathetic neural modulation of HR variability, increased above rest at -40 mmHg. These responses did not differ significantly between groups. CONCLUSIONS: These results suggest that gender differences in the cardiovascular responses to LBNP are not due to gross differences in modulation of the autonomic nervous systems.

Adult↗
PubMed2000

The impact of disease management on outcomes and cost of care: a study of low-income asthma patients.

An asthma disease management program designed specifically for low-income patients experiencing significant adverse events can improve health outcomes substantially, while lowering costs. The Virginia Health Outcomes Partnership aimed to help physicians in a fee-for-service primary care case management program manage asthma in Medicaid recipients. Approximately one-third of physicians treating asthma in an area designated as the intervention community volunteered to participate in training on disease management and communication skills. This large-scale study discovered that the rate of emergency visit claims for patients of participating physicians who received feedback reports dropped an average of 41% from the same quarter a year earlier, compared to only 18% for comparison community physicians. Although only a third of the intervention community physicians participated in the training, emergency visit rates for all intervention community physicians nonetheless declined by 6% relative to the comparison community among moderate-to-severe asthma patients when data for participating and nonparticipating physicians were combined. At the same time, the dispensing of some reliever drugs recommended for asthma increased 25% relative to the comparison community. A cost-effectiveness analysis projected direct savings to Medicaid of $3 to $4 for every incremental dollar spent providing disease management support to physicians. The results of this study demonstrate the potential this program offers, especially for Medicaid programs in other states that want to improve the care of their primary care case management networks and, at the same time, manage costs.

Anti-Asthmatic Agents↗
PubMed2000

Political economy of tobacco control in low-income and middle-income countries: lessons from Thailand and Zimbabwe. Global Analysis Project Team.

Crucial to the success of the proposed Framework Convention on Tobacco Control will be an understanding of the political and economic context for tobacco control policies, particularly in low-income and middle-income countries. Policy studies in Thailand and Zimbabwe employed the analytical perspective of political economy and a research strategy that used political mapping, a technique for characterizing and evaluating the political environment surrounding a policy issue, and stakeholder analysis, which seeks to identify key actors and to determine their capacity to shape policy outcomes. These policy studies clearly revealed how tobacco control in low-income and middle-income countries is also being shaped by developments in the global and regional political economy. Hence efforts to strengthen national control policies need to be set within the context of globalization and the international context. Besides the transnational tobacco companies, international tobacco groups and foreign governments, international agencies and nongovernmental organizations are also playing influential roles. It cannot be assumed, therefore, that the tobacco control strategies being implemented in industrialized countries will be just as effective and appropriate when implemented in developing countries. There is an urgent need to expand the number of such tobacco policy studies, particularly in low-income and middle-income countries. Comprehensive guidelines for tobacco policy analysis and research are required to support this process, as is a broader international strategy to coordinate further tobacco policy research studies at country, regional and global levels.

Developing Countries↗
PubMed1999

Cerebral lateralization: relationship of language and ideomotor praxis.

OBJECTIVE: To determine the relationship of language lateralization and hand preference to praxis performance following left and right hemispheric amobarbital-induced inactivations. BACKGROUND: Patients who are aphasic from left cerebral dysfunction also frequently exhibit ideomotor apraxia in which they make temporal, spatial, and postural errors of learned skilled movements. However, hemispheric lateralization of the systems mediating ideomotor praxis in patients with atypical cerebral language dominance (i.e., bilateral or right hemispheric language function) remains uncertain. METHODS: Subjects included 90 patients with intractable seizures who were undergoing the intracarotid amobarbital procedure (IAP) as part of their preoperative evaluation for epilepsy surgery. Hand preference was determined by the Benton Handedness Questionnaire. Praxis was assessed by the subject's performance when pantomiming the use of four pictured tools. RESULTS: During left IAP, patients with typical language dominance made more ideomotor apraxic errors than did patients with atypical language dominance. During right IAP, patients with atypical language dominance made more ideomotor apraxic errors than did patients with typical language dominance. Overall, patients with atypical language dominance made fewer ideomotor apraxic errors than did patients with typical language dominance. These relationships were present irrespective of hand preference. CONCLUSIONS: Language dominance is more closely associated with the laterality of temporal and spatial movement representations (i.e., ideomotor praxis dominance) than is hand preference. Patients with atypical language dominance exhibit more bilateral cerebral distribution of both language and praxis function.

Adult↗