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Biomedical subjects

K Wang

Publications and source records attributed to K Wang.

At least 487 records · Page 27Linked to original sources
PubMed1992

Chimeras of hepatic lipase and lipoprotein lipase. Domain localization of enzyme-specific properties.

Chimeric molecules between human lipoprotein lipase (LPL) and rat hepatic lipase (HL) were used to identify structural elements responsible for functional differences. Based on the close sequence homology with pancreatic lipase, both LPL and HL are believed to have a two-domain structure composed of an amino-terminal (NH2-terminal) domain containing the catalytic Ser-His-Asp triad and a smaller carboxyl-terminal (COOH-terminal) domain. Experiments with chimeric lipases containing the HL NH2-terminal domain and the LPL COOH-terminal domain (HL/LPL) or the reverse chimera (LPL/HL) showed that the NH2-terminal domain is responsible for the catalytic efficiency (Vmax/Km) of these enzymes. Furthermore, it was demonstrated that the stimulation of LPL activity by apolipoprotein C-II and the inhibition of activity by 1 M NaCl originate in structural features within the NH2-terminal domain. HL and LPL bind to vascular endothelium, presumably by interaction with cell surface heparan sulfate proteoglycans. However, the two enzymes differ significantly in their heparin affinity. Experiments with the chimeric lipases indicated that heparin binding avidity was primarily associated with the COOH-terminal domain. Specifically, both HL and the LPL/HL chimera were eluted from immobilized heparin by 0.75 M NaCl, whereas 1.1 M NaCl was required to elute LPL and the HL/LPL chimera. Finally, HL is more active than LPL in the hydrolysis of phospholipid substrates. However, the ratio of phospholipase to neutral lipase activity in both chimeric lipases was enhanced by the presence of the heterologous COOH-terminal domain, demonstrating that this domain strongly influences substrate specificity. The NH2-terminal domain thus controls the kinetic parameters of these lipases, whereas the COOH-terminal domain modulates substrate specificity and heparin binding.

Amino Acid Sequence↗
PubMed1992

Clonal variation of expression of the genes coding for plasminogen activators, their inhibitors and the urokinase receptor in HT1080 sarcoma cells.

The human sarcoma cell line HT1080 was found, by in situ hybridization, to consist of cells expressing various levels of urokinase (uPA) and tissue type (tPA) plasminogen activator (PA) suggesting clonal variation of expression of these genes. Colonies originating from single HT1080 cells were, therefore, established and screened for PA activity using a fibrin agarose overlay. Colonies inducing lysis (clone C+ and H+) or no lysis (clones B- and M-) were isolated and tested for mRNA levels of uPA, tPA, uPA receptor (uPAR) and the 3 PA inhibitors (PAI), PAI-1, PAI-2 and protease-nexin I. The different clones revealed considerable variation of expression of the different PA and PAI genes, with lysis-inducing clones expressing mainly the PA genes, whereas non-lysing clones demonstrated higher expression of the PAI genes. Amplification or loss of specific genes was excluded by Southern blotting. The protein levels of cellular and secreted PA and PAI determined by ELISA and Western blots demonstrated a pattern similar to that observed for PA and PAI mRNA concentrations, suggesting clonal differences either on the level of transcription or in RNA processing and/or stability. Due to complex interactions between PA and PAI, neither mRNA nor protein levels of the different genes were predictive for the amount of functional PA activity present in the supernatant or on the cell surface of the different clones. Receptor-bound uPA activity was found to be considerably higher in lysis-inducing than in non-lysing clones and the activity was dependent on neutralization by PAI-1 rather than on the level of uPAR mRNA.

Fibrinolysin↗
PubMed1992

Study of the relationship between estimates of enzyme kinetic parameters.

Previous indications of an intrinsic relationship between estimates of Km and Vmax calculated from the Michaelis-Menten equation have been explored further. A mathematically linear relationship could be established for the estimates of the two parameters. The relationship--the trend line--holds whether or not the experimental error is linked to the rate of reaction, the substrate concentration or both, provided that the distribution of errors is symmetrical. The practical implication is that enzyme variants with low values of Km and Vmax may not be distinguishable from those with high values of Km and Vmax.

Enzymes↗
PubMed1992

Lysine 480 is not an essential residue for ATP binding or hydrolysis by Na,K-ATPase.

Lysine 480 has been suggested to be essential for ATP binding and hydrolysis by Na,K-ATPase because it is labeled by reagents that are thought to react with the ATPase from within the ATP binding site. In order to test this hypothesis, Lys-480 was changed to Ala, Arg, or Glu by site-directed mutagenesis, and the resultant Na,K-ATPase molecules were expressed in yeast cells. The ATPase activity of each of the mutants was similar to the activity of the wild type enzyme indicating that Lys-480 is not essential for ATP hydrolysis. The binding of [3H]ouabain in both ATP-dependent and inorganic phosphate-dependent reactions was used to determine the apparent affinity of each mutant for ATP or Pi. The K0.5(ATP) for ouabain binding to phosphoenzyme formed from ATP was 1-3 microM for Lys-480, Arg-480, and Ala-480, whereas for Glu-480 the K0.5(ATP) was 18 microM. The K0.5(Pi) for ouabain binding to phosphoenzyme formed from inorganic phosphate was 16-28 microM for Lys-480, Arg-480, and Ala-480, but was 74 microM for Glu-480. The Kd for ouabain binding was similar for both the wild type and mutant Na,K-ATPase molecules (3-6 nM). These data indicate that the substitution of an acidic amino acid for lysine at position 480 appears to reduce the affinity of the Na,K-ATPase for both ATP and phosphate. It is concluded that Lys-480 is not essential for ATP binding or hydrolysis or for phosphate binding by Na,K-ATPase but is likely to be located within the ATP binding site of the Na,K-ATPase.

Adenosine Triphosphate↗
PubMed1992

Symmetrical adenovirus minichromosomes have hairpin replication intermediates.

A special class of panhandles (hairpin or foldback structures) arising from the replication of symmetrical adenovirus (Ad) minichromosome dimers and oligomers have been identified by two-dimensional gel electrophoresis. Hairpins provide evidence for replicative intermediates in the pathway for Ad complementary-strand synthesis. Furthermore, larger inverted sequences give Ad minichromosomes a replicative advantage.

Adenoviridae↗
PubMed1992

Cloning and functional characterization of a family of human and mouse somatostatin receptors expressed in brain, gastrointestinal tract, and kidney.

Somatostatin is a tetradecapeptide that is widely distributed in the body. It acts on multiple organs including brain, pituitary, gut, exocrine and endocrine pancreas, adrenals, thyroid, and kidneys to inhibit release of many hormones and other secretory proteins. In addition, it functions as a neuropeptide affecting the electrical activity of neurons. Somatostatin exerts its biological effects by binding to specific high-affinity receptors, which appear in many cases to be coupled to GTP-binding proteins. Here we report the cloning, functional expression, and tissue distribution of two different somatostatin receptors (SSTRs). SSTR1 and SSTR2 contain 391 and 369 amino acids, respectively, and are members of the superfamily of receptors having seven transmembrane segments. There is 46% identity and 70% similarity between the amino acid sequences of SSTR1 and SSTR2. Stably transfected Chinese hamster ovary cells expressing SSTR1 or SSTR2 exhibit specific somatostatin binding, with an apparently higher affinity for somatostatin-14 than somatostatin-28, and NH2-terminally extended form of somatostatin-14. RNA blotting studies show that SSTR1 and SSTR2 are expressed at highest levels in jejunum and stomach and in cerebrum and kidney, respectively. A SSTR1 probe hybridized to multiple DNA fragments in EcoRI digests of human and mouse DNA, indicating that SSTR1 and SSTR2 are members of a larger family of somatostatin receptors. Thus, the biological effects of somatostatin are mediated by a family of receptors that are expressed in a tissue-specific manner.

Amino Acid Sequence↗
PubMed1992

Low grade gliomas: comparison of intraoperative ultrasound characteristics with preoperative imaging studies.

Thirty-three patients with low grade gliomas were evaluated with preoperative computed tomography (CT), magnetic resonance (MR) and intraoperative ultrasound (IOUS). Six patients had undergone previous surgical exploration. Tumor borders were marked with cortical letters and corresponding depths calculated. Resection of tumor corresponded to these ultrasound dimensions. The histology of biopsy specimens from tumor and ultrasound determined margins was studied on formalin fixed permanent sections using hematoxylin and eosin (H&E) and immunocytochemistry (GFAP). Tumors were all seen on preoperative MR studies and most commonly showed a decreased T1 and increased T2 signal. Seven tumors showed variable enhancement with gadolinium. On CT two tumors were not seen, twenty-three tumors were hypodense and eight hyperdense. Three tumors showed variable CT contrast enhancement. All tumors were hyperechoic on ultrasound. Twenty-five (75%) tumors were well defined with distinct margins compared to adjacent brain. Eight tumors had poorly defined borders on ultrasound; five (62%) of these lesions had previously undergone surgery. Eight tumors invaded functional brain identified by stimulation mapping techniques (e.g., speech cortex), thus limiting the resection. Five resections were limited because of involvement of important anatomical structures (e.g., corpus callosum). Of the remaining 20 tumors, seventeen (85%) had ultrasound defined margins that were histologically free of solid tumor (normal brain or sparse atypical cells only). Low grade gliomas are readily identified and their margins well defined by intraoperative ultrasound regardless of preoperative imaging patterns. The results suggest that IOUS may enhance intraoperative delineation and extent of resection for low grade gliomas.

Adolescent↗
PubMed1992

Organization, structure, and function of 95 kb of DNA spanning the murine T-cell receptor C alpha/C delta region.

We have analyzed the organization, structure, and function of the murine T-cell receptor C alpha/C delta region. This region spans 94.6 kb of DNA and contains the C alpha and C delta genes, as well as the V delta 5, J delta 2, and 50 different J alpha gene segments. Within this sequence we have identified 15 new J alpha gene segments, 40 new 5' RNA splice signals, and 40 new DNA rearrangement signals for the J alpha gene segments. The murine C alpha/C delta sequence contains an exceptionally high level of coding sequence with over 5.7% of the total sequence found in the exons. This is much more than that found in the beta-globin locus and the HPRT locus. Using the sequence data obtained from the C alpha/C delta region, we have designed simple assays to test for J alpha gene segment transcription and to determine the level of polymorphism for simple repeat sequences among different inbred strains of mice using the polymerase chain reaction. Furthermore, comparisons of this 95 kb of sequence with the available sequence from homologous regions of other species have led to the identification of a highly conserved sequence that is present throughout vertebrates and in the mouse binds lymphocyte-specific nuclear proteins. Comparisons of a 10-kb region, which includes the C alpha gene in human and mouse, average 66% sequence similarity. These studies support the contention that large-scale DNA sequencing projects of homologous regions of mouse and human will provide powerful new tools for studying the biology and evolution of loci such as the T-cell receptor and for identifying and posing new questions about the functions of conserved sequences.

Amino Acid Sequence↗
PubMed1992

The influence of bilirubin on fluidity and rotational correlation times of human erythrocyte membrane.

The effects of bilirubin on the membrane motion parameters of human erythrocyte membrane were determined by the spin labelled ESR method. It causes a decrease in the order parameter and an increase in the corresponding fluidity of the lipid molecules. Bovine serum albumin was found to inhibit effectively the effects due to bilirubin. The disturbance to the organization of membrane molecules by bilirubin as well as the protective effects of serum albumin are discussed on the basis of the experimental results.

Bilirubin↗
PubMed1992

Renal ultrasonographic correlates of acute pyelonephritis.

To determine the frequency and clinical significance of ultrasonographically detectable alterations in renal volume and anatomy that are associated with acute pyelonephritis, 25 women underwent renal ultrasonography during the acute phase of their illness, and 21 of these patients underwent the procedure after receiving antimicrobial therapy. One patient had a predisposing anatomic abnormality (4%; 95% confidence interval, 0-12%), and one patient each (8%; 95% confidence interval, 0-19%) experienced focal complications (an intrarenal mass and perinephric fluid collection). The kidneys of the 21 evaluable patients were acutely swollen (mean, 20%; P = .0001); one or both kidneys were enlarged by greater than or equal to 15% in 17 (81%). Acute renal enlargement was associated with protracted pretherapy symptoms (P less than .01), leukocytosis (P less than .01), focal infectious complications (P less than .01), and prolonged hospitalization (P less than .05). Thus, ultrasonographically demonstrable renal swelling characteristically occurs in women with acute pyelonephritis but is usually apparent only in retrospect. The degree of swelling correlates with selected clinical parameters, and the frequency of underlying anatomic abnormalities and focal infectious complications is low.

Acute Disease↗
PubMed1992

Mouse hepatocyte membrane potential and chloride activity during osmotic stress.

Hepatocyte transmembrane potential (Vm) during osmotic stress responds as an osmometer, in part because of changes in membrane K+ conductance. This may contribute to the electromotive force that drives transmembrane Cl- fluxes. To test this, double-barreled ion-sensitive microelectrodes were used to measure changes in steady-state intracellular Cl- activity (aiCl) during osmotic stress applied to mouse liver slices. Hyperosmotic and hyposmotic conditions were created by rapidly switching to a solution in which sucrose concentrations were increased or reduced, respectively. Hyperosmotic stress [1.4 x control osmolality (280 mosmol/kgH2O)] decreased hepatocyte Vm 46% from -39 +/- 1 to -21 +/- 1 mV (SE; n = 16 animals). Corresponding aiCl increased twofold from 19 +/- 2 to 38 +/- 3 mM. This shifted the Cl- equilibrium potential (ECl) 19 mV, from -38 +/- 0.3 to -19 +/- 2 mV. Hyposmotic stress [0.71 x control osmolality (290 mosmol/kgH2O)] increased hepatocyte Vm 64% from -28 +/- 1 to -46 +/- 1 mV (SE; n = 13 animals). Corresponding aiCl decreased 0.53-fold from 17 +/- 1 to 8 +/- 1 mM. This shifted the ECl 20 mV from -26 +/- 2 to -46 +/- 3 mV. Thus hepatocyte aiCl is in electrochemical equilibrium with Vm. The paired measurements above were repeated after addition of K(+)-channel blockers quinine or Ba2+. Ba2+ (2 mM) had no effect on either Vm or aiCl during hyperosmotic stress; however, Ba2+ significantly inhibited changes in Vm and aiCl during hyposmotic stress. Effects of quinine (0.5 mM) on Vm and aiCl during both hyperosmotic stress and hyposmotic stress were similar to those of Ba2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Studies of electron spin resonance on bilirubin free radicals.

The nature of ESR signals derived from bilirubin-IX alpha has been studied by focusing on the samples treated with free radical generating and inhibiting systems, i.e. X-XOD, Fe/EDTA, SOD, mannitol/ascorbate, CO, KCN, etc. In all the cases, the stable signals comprise those originated from semiquinone radical (g = 2.0012) and superoxide free radical (g parallel = 2.041, g perpendicular = 2.0040). The superoxide is shown binding with certain metal ions chelated by bilirubin. The free radical scavengers are able to destroy these radicals. The kinetic curve of the regeneration of bilirubin radicals has been determined and the reaction follows a zero order mechanism. It is likely that both the physiological and toxic actions of bilirubin are related to the characters of its free radicals. Bilirubin is discussed as "active oxygen sink" in mammalians.

Bilirubin↗
PubMed1992

[The monitor method of immunization coverage].

A comprehensive monitor method of immunization coverage is suggested to be applied to the expanded program on immunization. The routine coverage reporting system should be set up combined with surveys in selected townships. The criteria for doing survey is expressed in the flow chart. Two sampling methods are presented based on the principle of lot quality assurance sampling (LQAS) and coverage rate could be estimated after the surveys.

Child↗
PubMed1992

[Discussion of the effect of occlusal factor on bruxism].

Controversy has been existed on the effect of occlusal factor on bruxism. The purpose of this study is to evaluate the effect of occlusal factor on bruxism by clinical examination and photo-occlusion analysis. The patient group and control group are selected for this study. The results show that (1) the occlusal status in centric occlusion and eccentric articulation of the patient and control group has no significant difference; (2) the occlusal contact strength and distribution in centric occlusion of the patient and control group has no significant difference; (3) occlusal interferences are existed in different extent both in patient group and control group. This expresses that most of the subjects can compensate this kind of occlusal disorder without feeling any discomfort; (4) This can be concluded that occlusal factor is not an major causal factor on bruxism.

Adolescent↗
PubMed1991

Cloning, expression, and protein interaction of human nebulin fragments composed of varying numbers of sequence modules.

Nebulin, a family of giant myofibrillar proteins of 600-900 kDa, contains a large number of highly conserved sequence repeats of 31-38 amino acids. To investigate the significance of this repeat, human skeletal muscle nebulin cDNA fragments encoding two, six, seven, eight, or fifteen repeat modules were expressed in high yield as nonfusion proteins in Escherichia coli with the pET3d plasmid vector. F-actin cosedimentation and solid phase binding assays demonstrated that all nebulin fragments, except the smallest two-module 67-mer, bound to muscle actin with high affinity under physiological ionic conditions. Solid phase binding assays also revealed that a six-module fragment, NB5, binds to myosin and C-terminal protein but fails to bind to tropomyosin, troponin, and tubulin. Furthermore, the binding of NB5 to actin was inhibited by both tropomyosin and troponin. Immunoelectron microscopic localization of NB5 indicated that this N-terminal region fragment is situated near the distal end of thin filaments in the sarcomere. These results indicate that nebulin is a giant protein with an unprecedently large number of actin-binding sites along its length and is anchored at the C terminus to the Z line in the sarcomere. Nebulin may function as a multifunctional template protein that regulates the length of thin filaments and participates in muscle activities by interacting with actin and myosin filaments in the sarcomere of skeletal muscles.

Actins↗