Monte Carlo studies of tethered membranes with attractive interactions.
Explore the source record for details and available documents.
Journal Article↗
Biomedical subjects
D Liu
Publications and source records attributed to D Liu.
Carbocyclic substrates for de novo purine biosynthesis. Enantiospecific synthesis and enantiospecificity of enzymatic utilization.
The carbocyclic analogues of phosphoribosylamine, glycinamide ribonucleotide, and formylglycinamide ribonucleotide have been prepared enantiospecifically from D-ribonic acid gamma-lactone. These carbocycles, which have the same absolute configuration as the natural D-ribose-derived intermediates of de novo purine biosynthesis, are utilized stoichiometrically by the initial enzymes of the pathway. A comparison of the enzymatic processing of the (-)-enantiomers with those of the racemates indicates that in some cases, the (+)-enantiomer acts to inhibit the enzymatic activity.
Acyltransferases↗
Dissection of the enhancer activity of beta-globin 5' DNase I-hypersensitive site 2 in transgenic mice.
The beta-globin locus control region (LCR) consists of four erythroid-specific DNase I-hypersensitive sites, which are necessary for high-level expression of the beta-like globin genes in erythroid tissues. One of these sites, designated 5'HS-2, functions as an erythroid-specific enhancer element in transfection and transgenic mouse experiments. Recent transfection experiments and studies of DNA-protein interactions have localized the 5'HS-2 enhancer to 18 nucleotides that contain a binding site for both the erythroid-specific factor nuclear factor erythroid 2 (NFE-2) and for activator protein 1 (AP-1). To define the sequences necessary for in vivo enhancer activity, several deletion mutants of 5'HS-2 were linked to the human beta-globin gene and their activity was tested in transgenic mice. Three upstream fragments of 5'HS-2 [341, 374, and 412 base pairs (bp)], each of which contained the NFE-2/AP-1 sequences, resulted in beta-globin expression at levels equivalent to or higher than those observed with the entire 732-bp 5'HS-2 fragment. In contrast, a 358-bp downstream portion of 5'HS-2, which lacked the NFE-2/AP-1 sequences, resulted in beta-globin expression at the low levels seen with the beta-globin gene alone. Removal of the NFE-2/AP-1 sequences by a 67-bp internal deletion resulted in similar low levels of beta-globin expression. A 100-bp 5' fragment that contained the NFE-2/AP-1 sequences resulted in beta-globin expression that was higher than the beta-globin gene alone but lower than the entire 5'HS-2 fragment or the three larger upstream fragments. These studies demonstrate that the NFE-2/AP-1 sequences are essential for enhancer activity of 5'HS-2 but that other sequences are required for full activity in vivo.
Animals↗
A 36-base-pair core sequence of locus control region enhances retrovirally transferred human beta-globin gene expression.
The locus control region of the human beta-globin cluster consists of four major DNase I hypersensitive sites (HS). When linked to globin genes, the locus control region confers a high level of erythroid-specific expression of these genes in transgenic mice or transfected erythroid cell lines. We have examined the effect of one of these sites, HS2, on human beta-globin gene expression in a murine erythroleukemia cell line (MEL) after retrovirus-mediated gene transfer. We incorporated a 732- or 412-base-pair (bp) segment of HS2 in the retroviral construct carrying the human beta-globin gene. These fragments rendered the viruses unstable as the human beta-globin gene was rearranged or deleted in all the packaging cell lines examined. On the other hand, when a 36-bp fragment containing the NFE-2/AP-1 binding consensus in this region was inserted into the retroviral construct, we recovered 6 stable packaging cell lines of 12 examined, similar in percentage to the construct with the beta-globin gene alone. The virus titers of the packaging cell lines from these two constructs were similar. We infected MEL cells with viruses produced from three packaging cell lines of each of the two constructs and measured the ratio of human beta-globin to mouse alpha-globin mRNA after hexamethylenebisacetamide induction. The overall level of expression increased 2-fold from 6.0% to 12.7% with the addition of this 36-bp enhancer.
3T3 Cells↗
Observation of photon-stimulated desorption following valence-band excitation of alkali halides.
Explore the source record for details and available documents.
Journal Article↗
Role of liposome size and RES blockade in controlling biodistribution and tumor uptake of GM1-containing liposomes.
We have examined the effect of liposome size on liposome circulation time in the blood. Liposomes composed of phosphatidylcholine, cholesterol and ganglioside GM1 were prepared in the various size range. Optimal circulation activity (55% injected dose at 4 h post injection) of GM1-containing liposomes, which correlated with a relatively high uptake of liposomes by EMT6 tumor in mouse, was obtained with a size range of 70 to 200 nm in diameter. Increasing the diameter of liposome to greater than 200 nm resulted in an enhancement of the spleen uptake and decrease of the blood level. For liposomes with a diameter of less than 70 nm, 70% of the injected dose were taken up by the liver, presumably by the parenchymal cells. In contrast, the biodistribution of phosphatidylserine-containing liposomes was relatively insensitive to changes in liposome size; most of the injected dose was found in the liver. The effect of RES blockade on the circulation time of large (d greater than 300 nm), GM1-containing liposomes was also studied. Dextran sulfate 500, a commonly used blockade reagent for Kupffer cells, had no effect. On the other hand, preinjection of a large dose of liposomes with a diameter greater than 500 nm showed variable results depending on the lipid composition of the blocking liposomes. Preinjection of liposomes containing GM1, phosphatidylinositol or (N-polyethyleneglycol) phosphatidylethanolamine effectively reduced the spleen uptake of the large GM1-containing liposomes, whereas liposomes containing phosphatidic acid showed no effect. These results indicate that only spleen homing liposomes can be used as a blocking reagent to prolong the circulation time of the large GM1-containing liposomes.
Animals↗
Raman scattering and lattice-dynamical calculations of crystalline KNO3.
Explore the source record for details and available documents.
Journal Article↗
Ion channel enzyme in an oscillating electric field.
To explain the electrical activation of several membrane ATPases, an electroconformational coupling (ECC) model has previously been proposed. The model explained many features of experimental data but failed to reproduce a window of the field intensity for the stimulated activity. It is shown here that if the affinities of the ion for the two conformational states of the transporter (one with binding site on the left side and the other on the right side of the membrane) are dependent on the electric field, the field-dependent transport can exhibit the observed window. The transporter may be described as a channel enzyme which opens to one side of the membrane at a time. It retains the energy-transducing ability of the earlier ECC models. Analysis of the channel enzyme in terms of the Michaelis-Menten kinetics has been done. The model reproduced the amplitude window for the electric field-induced cation pumping by (Na,K)-ATPase.
Adenosine Triphosphatases↗
Arterial, arterialized venous, venous and capillary blood glucose measurements in normal man during hyperinsulinaemic euglycaemia and hypoglycaemia.
The purpose of this study was to evaluate the effectiveness of the warm-air box method on the arterialization of venous blood during euglycaemia and hypoglycaemia. Six healthy male volunteers were studied using an i.v. infusion of insulin (144 mU.kg-1.h-1). Arterial blood glucose was clamped at the baseline level for the first 30 min and subsequently reduced to 3.2 and to 2.5 mmol/lf or 20 min. At each stage, including prior to insulin infusion, arterial, arterialized venous (heating the hand in a warm-air box set to 55-60 degrees C), venous and capillary blood samples were taken simultaneously for analyses of blood glucose and oxygen saturation (not for capillary blood). The oxygen saturations in arterialized blood were approximately 3% below the arterial values. The arterial-arterialized difference of blood glucose was about 0.1 mmol/l (the 95% confidence interval: from -0.19 to 0.41 mmol/l), which tended to correlate with the difference in oxygen saturations between the arterial and arterialized blood samples (r = 0.25, p = 0.08). During the test the forearm venous blood oxygen saturation increased by 9% and the arteriovenous difference in blood glucose ranged from 0.2 to 0.5 mmol/l which correlated significantly with the difference in oxygen saturations (r = 0.48, p less than 0.001). Capillary glucose was similar to the arterialized value. Rectal temperature was stable during the experiment.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Trypsin-induced lysis of lipid vesicles: effect of surface charge and lipid composition.
We have made a curious observation that the proteolytic enzyme, trypsin, induced a rapid and complete release of the contents of vesicles composed of dioleoylphosphatidylethanolamine (DOPE) and oleic acid (OA). Content release at 37 degrees C, monitored by the release of an entrapped fluorescence marker (calcein), was accompanied by an extensive vesicle aggregation. The lytic activity of trypsin on the vesicles depended on pH and liposome composition. The optimal pH for vesicle lysis was below pH 7.4, which was different from the optimal pH for catalytic activity of trypsin. The lytic activity of trypsin was specific for vesicles composed of DOPE and fatty acids such as OA and palmitoleic acid; vesicles composed of dioleoylphosphatidylcholine, N-methyl-DOPE, and OA, or DOPE combined with other negatively charged lipids such as phosphatidylserine and phosphatidic acid were not sensitive to trypsin. Inhibition of enzyme activity by trypsin inhibitors did not abolish the lytic activity, suggesting that the lytic activity of trypsin is not related to the catalytic activity. However, the lytic activity of trypsin on vesicles composed of DOPE and OA was inhibited in the presence of excess vesicles containing negative charges, or by a pretreatment of trypsin with acylating reagent to reduce the positive-charge content of trypsin. These data demonstrate that vesicle aggregation and lysis are the results of electrostatic interactions of positive charges on trypsin and negative charges on the vesicles. Phase separation and transition to nonbilayer phases of the vesicle lipids are likely involved.
Fluoresceins↗
A strategy for production of monoclonal antibodies to Echinococcus granulosus antigen 5 and antigen B.
Serum antibody responses to sheep hydatid cyst fluid (SHCF) and a purified Antigen 5 (Ag5) were examined in ELISA, immunoelectrophoresis (IEP) and immunoprecipitation (IP) to facilitate production of monoclonal antibodies (MAb) to E. granulosus Ag5 and Antigen B (AgB). Although sera from mice immunized with SHCF contained antibodies of various classes, the fusions using these donor mice resulted in mainly anti-AgB MAb, possibly due to the preferential selection of MAb to AgB by the SHCF-based ELISA screening system. Donor mice immunized with Ag5 also produced several classes of antibodies, and the resultant fusions enabled selection of IgG MAb to Ag5.
Animals↗
Comparative immunoelectrophoretic analysis of Echinococcus granulosus, Taenia hydatigena and Taenia pisiformis cyst fluid antigens by hyperimmune rabbit sera.
Cyst fluid antigens of Echinococcus granulosus, Taenia hydatigena and T pisiformis were examined by electrophoresis using homologous and heterologous hyperimmune rabbit sera to these antigens. While arc 5 forming antibodies were identified in sera from rabbits immunised with E granulosus and T hydatigena cyst fluids, antibodies responsible for forming precipitating antigen B band were detected in rabbit antisera to E granulosus, T hydatigena and T pisiformis antigens. T hydatigena cyst fluid appears to contain antigen similar to E granulosus antigen 5 and probably antigen B while T pisiformis cyst fluid has mainly an antigen close to hydatid antigen B.
Animals↗
Inhibitory effect of recombinant intracellular interleukin 1 receptor antagonist on endothelial cell activation.
This investigation was designed to elucidate whether an intracellular version of interleukin 1 receptor antagonist (icIL-1ra) interferes with the action of IL-1 at the level of vascular cells. Recombinant icIL-1ra inhibited the IL-1-induced production of IL-6, IL-8 and monocyte chemotactic protein by human endothelial cells (HEC). Moreover, icIL-1ra inhibited induction of adhesion molecules by IL-1. Endotoxin lipopolysaccharide (LPS), an IL-1 inducer, stimulated a spectrum of functions in EC similar to that activated by IL-1, but icIL-1ra did not interfere with the LPS activation of EC. This observation suggests that induction of extracellular IL-1 is not an important intermediate event in the response of EC to LPS. Unlike LPS-stimulated monocytes, EC exposed to different inducers did not express appreciable levels of IL-1ra mRNA transcripts as assessed by northern blot analysis. IL-1ra produced by mononuclear phagocytes, represents a negative regulator circuit of the action of IL-1 on EC and could be important in the control of vascular participation in inflammation and immunity.
Cell Adhesion Molecules↗
Resonance transduction of low level periodic signals by an enzyme: an oscillatory activation barrier model.
The overall rate of an enzyme catalyzed reaction is determined by the activation barrier of a rate-limiting step. If the barrier is oscillatory due to the intrinsic properties of a fluctuating enzyme, this enzymatic reaction will be influenced by a low level periodic electric field through the resonance transduction between the applied field and the oscillatory activation barrier. The ATP hydrolysis activity of a highly purified, detergent solubilized Ecto-ATPase from chicken oviduct was used to test the above concept. At 37 degrees C, this activity (1,800 mumols mg-1 min-1) was stimulated up to 47% (to 2,650 mumols mg-1 min-1) by an alternating electric field (AC), with a frequency window at 10 kHz. The maximal stimulation occurred at 5.0 V (peak-to-peak) cm-1. The potential drop across the dimension of the enzyme was approximately 10 microV (micelle diameter 20 nm). The activation barrier, or the Arrhenius activation energy, of the ATP splitting was measured to be 30 kT and the maximal barrier oscillation was calculated to be approximately 2.5 kT according to the oscillatory activation barrier (OAB) model. With the optimal AC field, full impact of the electric stimulation could be effected in much less than a second. The OAB model is many orders of magnitude more sensitive for deciphering low level periodic signals than the electroconformational coupling (ECC) model, although the latter has the ability to actively transduce energy while the former does not. By the OAB mechanism, the detecting limit of an external electric field by the ATPase, in a cell 20 micro m in diameter,would be 5 mV cm-1, but could be much lower for other membrane enzymes or receptors (e.g., nV cm-1). We propose that mechanisms similar to the OAB model could explain how a weak electromagnetic field or acoustic noises can exert its effects on an organism or a living cell.
Adenosine Triphosphatases↗
Further characterization of monoclonal antibodies to Echinococcus granulosus antigen 5 and antigen B.
Two monoclonal antibodies (24.14, 61A12) to Echinococcus granulosus Antigen 5 and two (31.15 and 39B3) to Antigen B were further characterized using modified sheep hydatid cyst fluid antigens (SHCF) in ELISA. None of these four monoclonals were directed against carbohydrate or lipid epitopes of SHCF antigens since they all reacted strongly with periodate or lipase-treated SHCF. On the other hand, they appeared to recognize SHCF determinants of protein nature as protease treatment of SHCF destroyed binding with the monoclonals. Anti-Antigen B monoclonals 31.15 and 39B3 showed strong reaction with boiled SHCF and anti-Antigen 5 monoclonal 24.14 did not. However, the second anti-Antigen 5 monoclonal 61A12 also reacted with boiled SHCF suggesting that some epitopes of Antigen 5 are heat stable. 24.14 and 61A12 may recognize a similar epitope of Antigen 5 whereas 39B3 may be against an epitope of Antigen B different from that recognized by 31.15.
Animals↗
B-cell lymphoma presenting as infiltrative renal disease.
Acute renal failure is rarely the presenting manifestation of non-Hodgkin's lymphoma. Of the reported cases of renal insufficiency secondary to diffuse renal infiltration with lymphoma, few have presented with acute renal failure. We present a patient with acute renal failure secondary to diffuse bilateral renal infiltration by a B-cell non-Hodgkin's lymphoma. The findings of an elevated serum lactate dehydrogenase (LDH), lymphopenia, and homogenous bilateral renal enlargement on computed tomographic (CT) imaging were important in suggesting the diagnosis of primary renal lymphoma. Renal biopsy with immunohistochemical and ultrastructural analysis was instrumental in confirming this diagnosis.
Acute Kidney Injury↗
Coproantigen detection for immunodiagnosis of echinococcosis and taeniasis in dogs and humans.
Three ELISA assays, based on hyperimmune rabbit serum raised against adult cestode somatic antigen, were applied in this study for the detection of Taenia- and Echinococcus-specific antigens in host faeces. The first assay, using an antiserum against Taenia pisiformis antigen extract, was used in a time-course of T. pisiformis experimental infection in dogs. The assay was shown to be considerably more sensitive than microscopical detection of eggs in faeces. Antigen was present in faeces before patency and antigen levels were independent of T. pisiformis egg output. The second assay, involving a test for human taeniasis based on antibodies against T. solium, was applied in two field studies carried out in China and Guatemala. The test was highly specific, no false positive reactions occurred with human faecal samples and the test was capable of diagnosing individuals who would not have been detected by coproscopy or treatment to recover the tapeworm. A third assay was designed for E. granulosus and demonstrated 87.5% sensitivity and 96.5% specificity with samples from naturally and experimentally infected dogs with Echinococcus or Taenia infections. In both the human Taenia and canine Echinococcus studies antigen could be detected in faecal samples from infected hosts stored in 5% formalin for 6 months. Further refinements to these tests for field application are discussed.
Animals↗
Evaluation of a monoclonal antibody-based competition ELISA for the diagnosis of human hydatidosis.
An antibody competition enzyme-linked immunosorbent assay (ELISA) using 4 different monoclonal antibodies (MAb) raised against major antigens (Antigen 5 and Antigen B) of Echinococcus granulosus was evaluated for the diagnosis of human hydatidosis. The competition assay, using anti-Ag5 MAb 24.14, detected specific antibodies in 70% (131/188) of sera from patients with surgically confirmed E. granulosus infection and 38.5% (10/26) of sera from patients with E. multilocularis infection. None of the sera from patients with Taenia solium cysticercosis (10), T. saginata (2), filariasis (22), strongyloidiasis (19), fascioliasis (4), bilharziasis (4) and amoebiasis (2) tested were positive using a cut-off point established through reaction between MAb 24.14 and normal human sera. The combined use of the MAb 24.14-based competition ELISA with the conventional antibody-binding assay provides a highly sensitive (92.8%) and specific screening system for human hydatid disease diagnosis.
Antibodies, Helminth↗