Biomedical subjects

D H Wu

Publications and source records attributed to D H Wu.

At least 19 recordsLinked to original sources

PubMed2006

Pressure-induced transition in magnetoresistance of single-walled carbon nanotubes.

We applied hydrostatic pressure (up to 10 GPa) to single-walled carbon nanotube bundles at low temperature (down to 2 K) to measure their magnetoresistance (MR) in a field up to 12 T. We found a pressure-induced transition in MR from positive to negative in the high-field regime. The onset of the transition occurs at approximately 1.5 GPa, which correlates closely with the tube shape transitions. The characteristics of the high-pressure MR are consistent with a model of pressure-induced two-dimensional weak localization.

Journal Article↗

PubMed2004

Determining incidence of extended spectrum beta-lactamase producing Enterobacteriaceae, vancomycin-resistant Enterococcus faecium and methicillin-resistant Staphylococcus aureus in 38 centres from 17 countries: the PEARLS study 2001-2002.

The PEARLS study prospectively monitored selected nosocomial pathogens from 38 centres in 13 European, three Middle Eastern countries and South Africa during 2001-2002. Extended spectrum beta-lactamase (ESBL) production rates among Escherichia coli, Klebsiella pneumoniae, and Enterobacter spp. were 5.4% (142/2609), 18.2% (401/2,206) and 8.8% (204/2,328), respectively, for all study sites. The overall ESBL production rate for the combined Enterobacteriaceae was 10.5% (747/7,143), highest in Egypt, 38.5%, and Greece, 27.4%, and lowest in The Netherlands, 2.0%, and Germany, 2.6%. IEF, PCR and DNA sequencing determined 10.7% false positives among Enterobacter spp. when using NCCLS guidelines to screen for ESBL production. The prevalence of nosocomial methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium was 32.4% (294/908) and 8.7% (83/949), respectively. PEARLS provides baseline data against which prospective changes in resistant determinants and outcomes can be measured in this ongoing study.

Anti-Bacterial Agents↗

PubMed2002

Direct synthesis of long single-walled carbon nanotube strands.

In the processes that are used to produce single-walled nanotubes (electric arc, laser ablation, and chemical vapor deposition), the typical lengths of tangled nanotube bundles reach several tens of micrometers. We report that long nanotube strands, up to several centimeters in length, consisting of aligned single-walled nanotubes can be synthesized by the catalytic pyrolysis of n-hexane with an enhanced vertical floating technique. The long strands of nanotubes assemble continuously from arrays of nanotubes, which are intrinsically long.

Journal Article↗

PubMed2001

Molecular cloning and characterization of a novel mammalian endo-apyrase (LALP1).

Here we describe the cloning, localization, and characterization of a novel mammalian endo-apyrase (LALP1) in human and mouse. The predicted human LALP1 gene encodes a 604-amino acid protein, whereas the mouse Lalp1 gene encodes a 606-amino acid protein. The human and mouse genes have 88% amino acid sequence identity. These genes share considerable homologies with hLALP70, a recently discovered mammalian lysosomal endo-apyrase. The human LALP1 gene resides on chromosome 10q23-q24 and contains 12 exons and 11 introns covering a genomic region of approximately 46 kilobase pairs. The subcellular localization and enzymatic activity of LALP1 indicated that LALP1 is indeed an endo-apyrase with substrate preference for nucleoside triphosphates UTP, GTP, and CTP.

Amino Acid Sequence↗

PubMed2001

Coiled coil region of streptokinase gamma-domain is essential for plasminogen activation.

The specific functions of the amino acid residues in the streptokinase (SK) gamma-domain were analyzed by studying the interactions of human plasminogen (HPlg) and SK mutants prepared by charge-to-alanine mutagenesis. SK with mutations of groups of amino acids outside the coiled coil region of SK gamma-domain, SK(K278A,K279A,E281A,K282A), and SK(D360A,R363A) had similar HPlg activator activities as wild-type SK. However, significant changes of the functions of SK with mutations within the coiled coil region were observed. Both SK(D322A,R324A,D325A) and SK(R330A,D331A,K332A,K334A) had decreased amounts of complex formation with microplasminogen and failed to activate HPlg. SK(D328A,R330A) had a 21-fold reduced catalytic efficiency for HPlg activation. The studies of SK with single amino acid mutation to Ala demonstrate that Arg(324), Asp(325), Lys(332), and Lys(334) play important roles in the formation of a HPlg.SK complex. On the other hand, amino acid residues Asp(322), Asp(328), and Arg(330) of SK are involved in the virgin enzyme induction. Potential contact between Lys(332) of SK and Glu(623) of human microplasmin and strong interactions between Asp(328) and Lys(330), Asp(331) and Lys(334), and Asp(322) and Lys(334) of SK are noticed. These interactions are important in maintaining a coiled coil conformation. Therefore, we conclude that the coiled coil region of SK gamma-domain, SK(Leu(314)-Ala(342)), plays very important roles in HPlg activation by participating in virgin enzyme induction and stabilizing the activator complex.

Base Sequence↗

PubMed2001

Superior mesenteric arteriovenous fistula associated with portal obstruction.

Superior mesenteric arteriovenous fistula is rarely encountered. Unrecognized in early stage, it can cause hazardous sequelae of portal hypertension. Herein we report a rare case of portal obstruction associated with an aneurysmal dilatation of the superior mesenteric vein, which was caused by a superior mesenteric arteriovenous fistula. The patient was a 74-year-old woman admitted for continuous hemetemesis, presenting with a palpable abdominal mass. The computed tomogram revealed a 6.5 cm superior mesenteric venous aneurysm and thrombotic portal venous obstruction. On account of impending shock, an emergent portal venous thrombectomy and portocaval shunt was carried out. Superior mesenteric arterial angiography performed 4 months later confirmed the diagnosis. Being without symptoms, the patient was clinically followed and remained in stable condition for 3 and a half years. The clinical presentation of a mesenteric arteriovenous fistula varies, with occasional gastrointestinal tract hemorrhage. When complicated with portal obstruction, the condition can be disastrous. We believe that creation of a porto-systemic shunt with resection of the arterio-venous fistula is the proper treatment. This patient is now under close observation.

Aged↗

PubMed2000

Terephthalaldehyde bis(thiosemicarbazone) bis(dimethylformamide) solvate.

The thiosemicarbazone molecule in C(10)H(12)N(6)S(2).2C(3)H(7)NO has -1 symmetry. The thiosemicarbazone moiety and the benzene ring are essentially coplanar, with mean and maximum deviations of 0.03 and 0. 11 A, respectively. The dimethylformamide molecules bridge the thiosemicarbazone moieties, forming two-dimensional sheets through N-H.O hydrogen bonds.

Journal Article↗

PubMed1998

Plasminogen activation by streptokinase via a unique mechanism.

The mechanism of human plasminogen (HPlg) activation by streptokinase (SK)-type activator was investigated with recombinant truncated SK peptides. An enzyme-substrate intermediate of HPlg.SK. HPlg ternary complex was demonstrated by a sandwich-binding experiment. Formation of the ternary complex was saturable, HPlg-specific, and inhibited by 6-aminocaproic acid. Three interaction sites between SK and HPlg were demonstrated. SK-(220-414) bound to HPlg with two binding sites: one to the micro-HPlg region, the catalytic domain of HPlg, and one to the kringle 1-5 region, with Kd values of 1.50 x 10(-7) and 2.44 x 10(-6) M, respectively. SK-(16-251) bound to a single site on the kringle 1-5 region of HPlg with a Kd of 4.09 x 10(-7) M. SK-(220-414) and SK-(16-251) competed for binding on the same or nearby location on the human kringle 1-5 domain. Combination of SK-(220-414) and SK-(16-251), but not either peptide alone, could effectively activate HPlg. In addition, SK-(16-251) dose-dependently enhanced the activation of HPlg by SK-(16-414), while the HPlg activation by SK-(16-414) was inhibited by SK-(220-414). We conclude that the HPlg that binds to the COOH-terminal domains of SK functions as an enzyme to catalyze the conversion of substrate HPlg that binds to the NH2-terminal domain of SK to human plasmin.

Aminocaproic Acid↗

PubMed1998

Preparation of a novel streptokinase mutant with improved stability.

The novel mutant streptokinase, SK-K59E, can activate human plasminogen as efficiently as the purified commercially available streptokinase. Several peptide bonds including Lys59-Ser60 in native streptokinase were hydrolyzed in reaction with plasmin and peptides of small molecular masses were generated. The plasminogen activator activity of native streptokinase in reaction with human plasmin declined to 25% of the original activity in a 120-min incubation. On the other hand, the NH2-terminal peptide of SK-K59E remained intact in reaction with plasmin and the activator activity of streptokinase decreased to 75% of the original activity in 120 min. The major degraded peptide fragments of native streptokinase in reaction with plasmin had molecular masses of 36 and 30 kDa. However, two major peptide fragments of 42 and 34 kDa were observed in the reaction of SK-K59E with human plasmin. The 42 kDa peptide fragment, which contained NH2-terminal of streptokinase, could activate human plasminogen as efficiently as the native streptokinase. SK-K59E can induce greater degree of caseinolysis and fibrinolysis than the native streptokinase. In conclusion, the results demonstrate that the prevention of cleavage at Lys59 of streptokinase prolongs the half-life of streptokinase in complex with plasmin and that the NH2-terminal of streptokinase (Ile1-Lys59) plays an important role in maintaining its stability.

Enzyme Stability↗

PubMed1997

Isolation of six low molecular weight heat shock proteins and partial characterization of heat shock protein 29 from mung bean hypocotyl.

Heat shock protein (HSP29) together with five other low-M(r) HSPs have been isolated from mung bean hypocotyls by preparative continuous elution SDS-PAGE. Autoradiography and immunochemical analysis of 2D electrophoretograms of the radiolabelled HSP29 revealed that it consists of seven isotypes, two of which are constitutive while the other five are heat-inducible. The pI values of the seven isotypes range from 4.6 to 6.6. A monoclonal antibody raised against the HSP29 isolate reacted with six of the seven isotypes. When HSP29 was subjected to partial proteolysis by V8 Staphylococcus aureus protease (EC 3.4.21.19), two fragments of 12 and 17 kDa were identified, neither of which was recognized by the antibody.

Antibodies, Monoclonal↗

PubMed1997

Functional MR to localize sustained visual attention activation in patients with attention deficit hyperactivity disorder: a pilot study.

PURPOSE: To evaluate brain control activation in patients with attention deficit hyperactivity disorder (ADHD) and to provide an initial comparison between activated regions in ADHD subjects and those previously localized in an unaffected population. METHODS: Ten patients with ADHD underwent imaging with a functional blood oxygen level-dependent MR technique during sustained visual vigilance. Pixel activation was inspected visually and statistical group analysis was performed. RESULTS: Activation was seen over the bilateral middle frontal gyri, the superior parietal lobules, and the inferior parietal lobules. The predominant activity occurred in the right middle frontal gyrus. Application of an additional statistical constraint revealed significant activity in the right inferior and left superior parietal lobules. CONCLUSION: ADHD patients effectively tolerated the necessary MR imaging constraints despite their difficulty with confinement and immobility. Single-section functional MR imaging revealed activation in brain regions known to be involved in the maintenance of the attention in healthy subjects responding to auditory, tactile, or visual stimulation; additional areas of activity that were identified may represent true abnormal regions in the affected population or artifacts.

Adolescent↗

PubMed1994

Function of streptokinase fragments in plasminogen activation.

Several peptide fragments of streptokinase (SK) were prepared by incubating SK with immobilized human plasmin (hPlm) and purified by h.p.l.c. with a reverse-phase phenyl column. The N-terminal sequences, amino acid compositions and molecular masses of these peptide fragments were determined. The SK peptide fragment of 36 kDa consisting of Ser60-Lys387 (SK-p), was the only peptide fragment that could be tightly bound to immobilized hPlm. Another three large SK peptide fragments, SK-m, SK-n and SK-o, with molecular masses of 7 kDa, 18 kDa and 30 kDa, and consisting of Ile1-Lys59, Glu148-Lys333, Ser60-Lys333 respectively, were also obtained from the supernatant of the reaction mixture. The purified SK-p had high affinity with hPlm and could activate human plasminogen (hPlg) with a kPlg one-sixth that of the native SK. SK-o had low affinity with hPlm and could also activate hPlg, although the catalytic constant was less than 1% of the native SK. SK-n, as well as SK-m, which is the N-terminal 59 amino acid peptide of the native SK, had no activator activity. However, SK-m could enhance the activator activity of both SK-o and SK-p and increase their second-order rate constants by two- and six-fold respectively. It was concluded from these studies that (1) SK-o, the Ser60-Lys333 peptide of SK, was essential for minimal SK activator activity, (2) the C-terminal peptide of SK-p, Ala334-Lys387, was essential for high affinity with hPlm, and (3) the N-terminal 59-amino-acid peptide was important in maintaining the proper conformation of SK to have its full activator activity.

Amino Acid Sequence↗

PubMed1993

Interaction of immobilized human plasminogen and plasmin with streptokinase.

The complex of immobilized human plasminogen (iHPlg) and streptokinase (SK) has a lower catalytic activity in hydrolysis of plasmin-specific substrate S-2251 with a kcat/Km of 0.005 microM-1 x s-1, compared to 0.031 microM-1 x s-1 of immobilized human plasmin (iHPlm) and 0.078 microM-1 x s-1 of HPlm. The SK in the complex could be removed by acid buffer solution, and the iHPlg will remain catalytically active. IHPlm.SK complex could activate bovine plasminogen (BPlg), whereas iHPlg.SK complex could not. IHPlg could be activated by interaction with a combination of SK and HPlg or urokinase. The activated iHPlg.SK complex had the ability to activate BPlg as iHPlm.SK. The reasonable explanation is that iHPlg was converted to iHPlm in reaction with the combination of HPlg and SK. However, iHPlg was converted to a virgin enzyme in reaction with SK alone and could not activate BPlg. A new modified mechanism for the interaction of HPlg or HPlm with SK was proposed.

Amidohydrolases↗

PubMed1992

The binding of plasminogen fragments to cultured human umbilical vein endothelial cells.

Glu-plasminogen, kringle 1-5, kringle 1-3, and miniplasminogen exhibited strong binding to human umbilical vein endothelial cells (HUVEC). On the other hand, no significant binding was obtained with microplasminogen and kringle 4. Kringle 1-5 and miniplasminogen, which both contained kringle 5, specifically inhibited the binding of plasminogen to HUVEC while kringle 1-3 did not. The results implied plasminogen molecule contained at least two binding sites, with which it interacted HUVEC. The stronger binding site was located in kringle 5 and the weaker one was in kringle 1-3. Kringle 4 and the active site domain exhibited no significant binding to HUVEC. The interaction of plasminogen with HUVEC is mainly through binding site on kringle 5.

Amino Acid Sequence↗

PubMed1991

Kringle domains and plasmin denaturation.

The rate of plasmin denaturation was in the order of Lys-plasmin greater than miniplasmin greater than microplasmin. Fibrinogen degradation products (FDP) dose dependently increased the denaturation rate of Lys-plasmin and mini-plasmin with a maximal rate constant at the FDP/plasmin ratio of about 0.5. The denaturation rate constant of microplasmin was not affected. FDP increased the rate of plasmin denaturation was in parallel with its effect on the interaction among kringle domains. Without FDP only trace amounts of plasminogen dimer could be detected by cross-linking with bis-(sulfo-succinimidyl)-suberate followed by SDS gel electrophoresis. In the low concentration of FDP significant amounts of oligomers of Glu-, mini-plasminogens, kringle 1-3 and kringle 1-5 were observed. High concentration of FDP, however, decreased plasminogen oligomer.

Amino Acid Sequence↗

PubMed1991

Efficacy and tolerability of cefixime in otitis media. A multicentre study in over 25,000 children.

A large scale multicentre clinical study was undertaken to assess the efficacy and tolerability of cefixime in the treatment of acute otitis media in children. A total of 25,863 evaluable children with acute otitis media received cefixime 8 mg/kg once daily for at least 10 days. At the end of treatment, 86% of patients were considered to be either cured or improved. These results are consistent with those achieved with cefixime in controlled clinical trials. Adverse effects were reported in 11.5% of patients, but were judged to be related to cefixime therapy in only 9.4% of patients. The results of this study demonstrate that cefixime is an effective and well tolerated treatment for acute otitis media in children.

Acute Disease↗

PubMed1990

Interaction of plasminogen and fibrin in plasminogen activation.

Glu1-, Lys77-, miniplasminogens, kringle 1-3, kringle 1-5A, and kringle 1-5R were able to bind with fibrin, while microplasminogen and kringle 4 did not bind significantly. Kringle 1-5A, but not kringle 1-3, effectively inhibited the binding of Glu1-, Lys77-, and miniplasminogens with fibrin. Miniplasminogen also inhibited the binding of Glu1-plasminogen with fibrin. The binding of kringle 1-3 with fibrin was blocked by mini- or Glu1-plasminogen. It is therefore evident that there are two fibrin-binding domains in plasminogen and that the one in kringle 5 is of higher affinity than that in kringle 1-3. CNBr cleavage products of fibrinogen effectively enhanced the activation of Glu1-, Lys77-, or miniplasminogens, but not microplasminogen, by tissue-type plasminogen activator. Kringle 1-5, but not kringle 1-3, dose-dependently inhibited the enhancement by fibrinogen degradation products of Glu1-plasminogen activation by the activator. Lysine and epsilon-aminocaproic acid could inhibit the binding of plasminogens and plasminogen derivatives with fibrin and block the enhancement effect of fibrinogen degradation products on plasminogen activation. The data clearly illustrate that the binding of plasminogen with fibrin, mainly determined by kringle 5, is essential for effective activation by tissue-type plasminogen activator. However, the presence of kringle 1-4 in the plasminogen molecule is required for the full enhancing effect since the kcat/Km of miniplasminogen activation in the presence of fibrinogen degradation products was 8.2 microM-1 min-1 which is significantly less than 52.0 microM-1 min-1 of Glu1-plasminogen.

Aminocaproic Acid↗

PubMed1990

Activation of human and bovine plasminogens by the microplasmin and streptokinase complex.

Human microplasmin is a catalytically active fragment of human plasmin. It consists of a 31-residue C-terminal peptide derived from the A chain bound through two disulfide bonds to the intact B chain of plasmin. It has similar amidolytic and proteolytic activities as the native human Lys-plasmin on a molar basis. Human microplasmin can form a complex with streptokinase, in a one to one stoichiometry, like the native human Lys-plasmin. The stoichiometric human microplasmin and streptokinase complex is an efficient activator of bovine plasminogen which can not be activated by streptokinase alone. The formation of human microplasmin.streptokinase complex was also directly demonstrated by a gel filtration column chromatography. Moreover, bovine plasminogen can not be activated by a mixture of bovine or porcine microplasmin and streptokinase. The equimolar complex of human microplasmin.streptokinase, human Lys-plasmin.streptokinase, or streptokinase alone has the same activator activity toward human Lys-plasminogen. The human microplasmin.streptokinase complex, however, has a significantly higher activator activity than human Lys-plasmin.streptokinase complex or streptokinase alone toward human Glu-plasminogen. The direct interaction between streptokinase and light chain domain of human plasmin is demonstrated in the complex formation. The difference in the activator activities of plasmins from various animal sources in complex with streptokinase therefore might be due to the difference in the compositions of light chains of plasmins.

Amino Acid Sequence↗