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Biomedical subjects

G Wang

Publications and source records attributed to G Wang.

At least 595 records · Page 33Linked to original sources
PubMed1997

[The new parameters of motor unit potential in the diagnosis of neurogenic lesions in spike-triggered averaging electromyography].

OBJECTIVE: To evaluate the clinical significance of the new parameters of motor unit potential (MUP) to the diagnosis of neurogenic lesions. METHODS: Three groups of muscles, anterior tibialis, abductor pollicis brevis and vastus medialis were studied with spike-triggered averaging electromyography (EMG). A total of 3,646 MUPs, 1,903 from normal group and 1,743 from neurogenic group, were recorded under slight muscle contraction. RESULTS: The area, as a single parameter, produced the most significant result in discriminant analysis, about 80% MUPs from neurogenic muscles being judged to be abnormal. Compared with the area, the amplitude and duration were less sensitive, being able to assign about 77% and 70% of MUPs in the neurogenic group as abnormal. A combination of the area/amplitude ratio (thickness) and the amplitude, and a combination of the duration (width) and the amplitude could further improve the discriminating ability, around 80% and 81% MUPs in the neurogenic muscles being classified as abnormal by the combinations. The simplified discriminant functions, 2 x Log10 (amplitude) +Log10 (area/amplitude) -4 for size index, and 5 x Log10 (duration) + 3 x Log10 (amplitude) -10 for width-height index had same discriminating ability as the real discriminant function. CONCLUSIONS: The new parameters, SI, WHI and area in spike-triggered EMG seemed to be promising, since they produced a better yield in the diagnosis of neurogenic lesions than amplitude or duration alone in the discriminant analysis.

Adolescent↗
PubMed1997

[Three-dimensional reconstruction of sinusoids from serial sections].

The three-dimensional image of sinusoids has been reconstructed by computer image processing using a new method of registration. By observing the reconstructed image of sinusoids, we can easily understand the anatomy of sinusoids. Theoretical analysis and experimental results suggest that the method is feasible and practicable.

Animals↗
PubMed1997

[Detection of human cytomegalovirus infection in blood donor population by the polymerase chain reaction].

Samples of peripheral blood from 76 different donors were detected for the presence of human cytomegalovirus (HCMV) DNA by polymerase chain reaction (PCR). The results showed that HCMVs were present in 39 out of 76 blood donors which reached an infection positive rate of 51.3%. In addition, the sensitivity and specificity on PCR were tested, it also indicated that the sensitivity can reach the level of 5fg.microliter-1. The method is simple, rapid, highly sensitive and specificity. It can be considered as a diagnostic measure in clinical detection of HCMV.

Blood Donors↗
PubMed1996

Large-Scale Synthesis of Aligned Carbon Nanotubes

Large-scale synthesis of aligned carbon nanotubes was achieved by using a method based on chemical vapor deposition catalyzed by iron nanoparticles embedded in mesoporous silica. Scanning electron microscope images show that the nanotubes are approximately perpendicular to the surface of the silica and form an aligned array of isolated tubes with spacings between the tubes of about 100 nanometers. The tubes are up to about 50 micrometers long and well graphitized. The growth direction of the nanotubes may be controlled by the pores from which the nanotubes grow.

Journal Article↗
PubMed1996

Probing conserved regions of the cytoplasmic LOOP1 segment linking transmembrane segments 2 and 3 of the Saccharomyces cerevisiae plasma membrane H+-ATPase.

Genetic probing was used to examine conserved amino acid clusters in the first cytoplasmic loop domain (LOOP1) linking transmembrane segments 2 and 3 of the plasma membrane H+-ATPase from Saccharomyces cerevisiae. Deletion of the LOOP1 region in PMA1 resulted in a defective enzyme. Scanning alanine mutagenesis of conserved residues produced lethal cell phenotypes in 14 of 26 amino acids, suggesting major enzyme defects. Most viable mutants showed growth characteristics that were comparable to wild type. Two mutations, I183A and D185A, produced reduced growth rates, hygromycin B resistance, and low pH sensitivity, which are phenotypes associated with defects in the H+-ATPase. However, both mutant enzymes displayed near-normal kinetics for ATP hydrolysis in vitro. Localized random mutagenesis was also performed at sites Glu195, Val196, and Ile210, which all showed lethal phenotypes upon conversion to alanine. Amino acids with polar side groups could substitute for Glu195, while Val196 could not tolerate polar side group moieties. Nine mutations at Ile210 proved lethal, including K, R, E, P, H, N, V, G, and A, while functional enzyme was obtained with S, C, M, and L. Normal rates and extents of pH gradient formation were observed for all mutant enzymes, except I183A and D185A. Detailed analysis of the I183A enzyme indicated that it hydrolyzed ATP like wild type, but it appeared to inefficiently couple ATP hydrolysis to proton transport. In total, these results affirm that conserved amino acids in LOOP1 are important to H+-ATPase function, and purturbations in this region can alter the efficiency of energy coupling.

Alanine↗
PubMed1996

On the bilayer phase transition temperatures for monoenoic phosphatidylcholines and phosphatidylethanolamines and the interconversion between them.

The dependence of the phase transition temperature, Tm, on the structural parameters of the lipid molecule has been firmly established for lipid bilayers composed of saturated phosphatidylcholines (PC) or phosphatidylethanolamines (PE). It is from such a dependence that conversions of Tm values from saturated PC to PE and vice versa have been successfully demonstrated. In this communication, similar chain-melting-structure relationships are sought for monoenoic PC and PE in which the long hydrocarbons linked at the sn-1 and sn-2 positions are saturated and cis-mono-unsaturated chains, respectively. Specifically, various molecular species of monoenoic PC and PE were first semisynthesized and their Tm values were subsequently determined by high-resolution differential scanning calorimetry. Based on the crankshaft-like kink motif model, the synthesized monoenoic PC and PE can each be divided into two groups, each group being characterized by three structural parameters. For each group of monoenoic PC or PE, a specific equation correlating the changes in Tm with variations in the structural parameters was derived using the multiple regression analysis. Furthermore, within each group of lipids including both PC and PE, an explicit equation describing the interconversion of Tm values between PC and PE with the same fatty acyl chain composition was established. The present work not only extends the earlier work relating the chain-melting temperature of saturated PC and PE to their structural parameters, but also indicates that the basic topology of the sn-2 mono-unsaturated acyl chain of PC and PE in the gel-state bilayer can be approximated by the crankshaft-like kink motif with the longer segment being packed much more orderly than the shorter segment.

Calorimetry, Differential Scanning↗
PubMed1996

Identification of a natural soluble form of the vascular endothelial growth factor receptor, FLT-1, and its heterodimerization with KDR.

A soluble form of the vascular endothelial growth factor (VEGF) receptor FLT-1 was identified in conditioned culture medium of human umbilical vein endothelial cells. The endogenous soluble FLT-1 (sFLT-1) receptor is chromatographically and immunologically similar to recombinant human sFLT-1 and binds [125I]VEGF with a comparable high affinity. Human sFLT-1 is shown to form a VEGF-stabilized complex with the extracellular domain of KDR in vitro, suggesting that not only full-length receptors are capable of forming ligand-induced heterodimeric complexes but also sFLT-1 can form a dominant negative complex with the mitogenically competent full-length KDR receptor.

Amino Acid Sequence↗
PubMed1996

A calorimetric study of binary mixtures of saturated and monounsaturated mixed-chain phosphatidylethanolamines.

In this study, we have semisynthesized the following three molecular species of mixed-chain phosphatidylethanolamine: C(22):C(12)PE, C(16):C(18:1 delta 9)PE, and C(10):C(24:1 delta 15)PE. These lipids share a common structural characteristic, that is, they all have the same total number of carbon atoms in their acyl chains. Aqueous dispersions prepared from three sets of binary lipid mixtures, C(16):C(18:1 delta 9)PE/C(22):C(12)PE, C(10):C(24:1 delta 15)PE/C(22):C(12)PE, and C(16):C(18:1 delta 9)PE/C(10):C(24:1 delta 15)PE, were studied by high-resolution differential scanning calorimetry, leading to the construction of three temperature-composition phase diagrams. A computer program developed on the basis of the thermodynamic equations for non-ideality of mixing (or Brigg-Williams approximation) was applied to fit the calorimetric data, yielding the non-ideality parameters of mixing in the gel and the liquid-crystalline bilayers (pG and pL). Based on the shapes of these phase diagrams and the values of pG and pL, it is concluded that any two of the three molecular species of phosphatidylethanolamines under study can mix nearly ideally in the bilayer plane of the liquid-crystalline bilayer. However, these binary lipid mixtures do exhibit the gel-gel phase immiscibility over an extensive compositional region in the gel-state bilayer. By comparison with experimental data obtained with binary mixtures of saturated identical-chain phospholipids, we can conclude that mixed-chain cis-monounsaturated lipid molecules and saturated lipid molecules are highly demixed in the same two-dimensional plane of the gel-state bilayer, although the bilayer thickness difference between the lipid bilayer composed of cis-monounsaturated lipids and that of saturated lipids may be only one or two C-C bond lengths at T < Tm.

Calorimetry, Differential Scanning↗
PubMed1996

Conformations of human apolipoprotein E(263-286) and E(267-289) in aqueous solutions of sodium dodecyl sulfate by CD and 1H NMR.

Structures of apoE(263-286) and apoE(267-289) have been determined in aqueous solution containing 90-fold molar excess of perdeuterated sodium dodecyl sulfate by CD and 1H NMR. Conformations were calculated by distance geometry based on 370 and 276 NOE distance restraints, respectively. RMSD for superimposing the region 265-284 from an ensemble of 41 structures for apoE(263-286) is 0.64 +/- 0.17 A for backbone atoms (N, C alpha, C = O) and 1.51 +/- 0.13 A for all atoms. The backbone RMSD for an ensemble of 37 structures for apoE(267-289) is 0.74 +/- 0.21 A for the region 268-275 and 0.34 +/- 0.10 A for the region 276-286. A two-domain structure was found for apoE(267-289) with the C-terminal half adopting a very well defined helix and the N-terminal segment 268-275 a less well defined helix, suggesting that the N-terminus may weakly bind to SDS. For apoE(263-286), an amphipathic helix-bend-helix structural motif was found with all hydrophobic side chains on the concave face. The existence of a bend around residues Q273 to G278 is consistent with their temperature coefficients of amide protons as well as secondary shifts of alpha-protons. Comparison of the structures of the two peptides revealed that the enhanced binding of apoE(263-286) to lipid could be attributed to the formation of a hydrophobic cluster consisting of residues W264, F265, L268, and V269. Aromatic side chains are proposed to be especially important in anchoring apolipoprotein fragments to micelles.

Amino Acid Sequence↗
PubMed1996

Topological folding and proteolysis profile of P-glycoprotein in membranes of multidrug-resistant cells: implications for the drug-transport mechanism.

P-glycoprotein (Pgp)1 is a polytopic membrane protein and functions as an energy-dependent drug efflux pump. It is responsible for multidrug resistance (MDR) in cancer cell lines. Recently, the topological structure of Pgp has been investigated. However, the results are in dispute. A major question concerning the Pgp topology is the membrane orientation of the loop linking TM4 and TM5 (loop 4) and the loop linking TM8 and TM9 (loop 8). In this study, we generated polyclonal antibodies specific to these two loops. In combination with a panel of other well-characterized site-specific polyclonal- and monoclonal antibodies of Pgp, we tested the membrane orientation of these two loops of Pgp in multidrug-resistant cells using immunocytochemistry and proteolysis/membrane protection assay. Our results showed that (1) both loops 4 and 8 are located extracellularly whereas other domains, such as the ATP-binding sites, are in the cytoplasm and (2) proteolysis of Pgp is not a random event and the trypsin-sensitive sites are cleaved in orders. Since the Pgp was not genetically manipulated in this study, in contrast to previous studies, we believe that naturally expressed Pgp molecules have an unconventional topology. We speculate that this alternate topology of Pgp may represent a different functional state of the protein. Further detailed analysis of Pgp topology will help to understand the fundamental mechanism of drug transport by Pgp.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Induction of the Escherichia coli UVM response by oxidative stress.

UVM (ultraviolet modulation of mutagenesis) is a recently described recA-independent, inducible mutagenic phenomenon in which prior UV irradiation of Escherichia coli cells strongly enhances mutation fixation at a site-specific 3-N4-ethenocytosine (epsilon C) lesion borne on a transfected single-stranded M13 DNA vector. Subsequent studies demonstrated that UVM is also induced by alkylating agents, and is distinct from both the SOS response and the adaptive response to alkylation damage. Because of the increasing significance being attributed to oxidative DNA damage, it is interesting to ask whether this class of DNA damage can also induce UVM. By transfecting M13 vector DNA bearing a site-specific epsilon C lesion into cells pretreated with inducing agents, we show here that the oxidative agent H2O2 is a potent inducer of UVM, and that the induction of UVM by H2O2 does not require oxyR-regulated gene expression. UVM induction by H2O2 appears to be mediated by DNA damage, as indicated by the observation of a concomitant reduction in cellular toxicity and UVM response in OxyRc cells. Available evidence suggests that UVM represents a generalized cellular response to a broad range of chemical and physical genotoxicants, and that DNA damage constitutes the most likely signal for its induction.

Bacteriophage M13↗
PubMed1996

Optical imaging of functional organization in the monkey inferotemporal cortex.

To investigate the functional organization of object recognition, the technique of optical imaging was applied to the primate inferotemporal cortex, which is thought to be essential for object recognition. The features critical for the activation of single cells were first determined in unit recordings with electrodes. In the subsequent optical imaging, presentation of the critical features activated patchy regions around 0.5 millimeters in diameter, covering the site of the electrode penetration at which the critical feature had been determined. Because signals in optical imaging reflect average neuronal activities in the regions, the result directly indicates the regional clustering of cells responding to similar features.

Animals↗
PubMed1996

Conformation of human serum apolipoprotein A-I(166-185) in the presence of sodium dodecyl sulfate or dodecylphosphocholine by 1H-NMR and CD. Evidence for specific peptide-SDS interactions.

The segment, YSDELRQRLAARLEALKENG, corresponding to residues 166 to 185 of human serum apolipoprotein A-I, was studied by circular dichroism and NMR spectroscopy in sodium dodecyl sulfate and dodecylphosphocholine micelles. 2-Dimensional NOESY, TOCSY and DQF-COSY spectra of apoA-I(166-185) in perdeuterated sodium dodecyl sulfate (SDS-d25) and dodecylphosphocholine (DPC-d38) micelles were collected at a peptide/SDS (DPC) ratio of 1:40. Similar CD spectra and NOE connectivity patterns were observed for apoA-I(166-185) in SDS and DPC, indicating a similar helical conformation in both. Conformations of apoA-I(166-185) in DPC-d38 micelles, and in SDS-d25 micelles at two pH values, 6.6 and 3.7, were determined using distance geometry calculations. Backbone superposition (N,C alpha,C = O) for an ensemble of twenty-nine structures in DPC at pH 6.0 gave a RMSD of 0.45 +/- 0.09 A for the region D168 to K182, while for all atoms it was 1.60 +/- 0.17 A. In SDS, the ensemble of nineteen structures each at pH 6.6 and 3.7 gave RMSDs of 0.28 +/- 0.07 A and 0.35 +/- 0.10 A, respectively, for the region D168 to K182. RMSD for superposition of all atoms was 1.36 +/- 0.10 A and 1.38 +/- 0.21 A at the respective pH values. In all cases a highly defined class A amphipathic helical structure was found for the region R171 to K182. Since the same structure occurs in micelles with either negatively charged or zwitterionic head groups it strongly suggests a dominant role for hydrophobic interactions in stabilizing the complex. The Y166 aromatic ring is bent back upon the helix axis at the lower pH. NMR determination of pKa values for D168, E169, E179 and E183 in the presence of SDS or DPC indicated a micro-pH at the micellar surface approximately one pH unit higher than the normal residue pKa. SDS interactions with the peptide were examined by collecting 1H NOESY spectra in the presence of protiated SDS. Residues R171, R173, R177, as well as the aromatic ring of Y166, were shown by intermolecular NOE measurements to interact with SDS, hence a key interaction in stabilizing the complex appears to be between interfacial basic side-chains and SDS alkyl chains.

Amino Acid Sequence↗
PubMed1996

Retrovirus-mediated transfer of the human O6-methylguanine-DNA methyltransferase gene into a murine hematopoietic stem cell line and resistance to the toxic effects of certain alkylating agents.

O6-Methylguanine-DNA methyltransferase (MGMT) is an important DNA repair protein that plays a key role in cancer chemotherapy by alkylating agents such as carmustine (BCNU) and Dacarbazine (DTIC). Therapy by BCNU and DTIC is reduced by dose-limiting hematological toxicity as a result of low MGMT repair activity in bone marrow cells. In this study, we have constructed a Moloney murine leukemia virus retroviral vector containing the human mgmt gene. High-titer retrovirus producer cells lines have been generated. Retroviral-mediated transfer of the human mgmt gene into murine multi-potent hematopoietic stem cells, FDCP-1, resulted in the expression of a high level of MGMT activity. In comparison with the control cells that were transduced with the parent vector, the MGMT-expressing clones were considerably more resistant to the cytotoxicity of the methylating agents, such as N-methyl-N'-nitro-N-nitrosoguanidine, N-nitroso-N-methyl-urea, and temozolomide, as well as the chloroethylating agents 1-(2-chloroethyl)-1-nitrosourea and BCNU. The protection provided by MGMT could be eliminated by the MGMT inactivator O6-benzylguanine. Thus, the principal lethal lesions produced by these alkylating agents in the murine hematopoietic stem cells and the MGMT deficiency in these cells can be complemented by retroviral-mediated gene transduction.

3T3 Cells↗
PubMed1996

Probing the cytoplasmic LOOP1 domain of the yeast plasma membrane H(+)-ATPase by targeted factor Xa proteolysis.

The cytoplasmic domain linking transmembrane segments 2 and 3 (LOOP1) of the yeast H(+)-ATPase was probed by the introduction of unique factor Xa recognition sites. Three sites, I170EGR, I254EGR and I275EGR, representing different structural regions of the LOOP1 domain, were engineered by site-specific mutagenesis of the PMA1 gene. In each case, multiple amino acid substitutions were required to form the factor Xa sites, which enabled an analysis of clustered mutations. Both I170EGR and I275EGR-containing mutants grew at normal rates, but showed prominent growth resistance to hygromycin B and sensitivity to low external pH. The engineered I254EGR site within the predicted beta-strand region produced a recessive lethal phenotype, indicating that mutations G254I and F257R were not tolerated. Mutant I170EGR- and I275EGR-containing enzymes showed relatively normal Km and Vmax values, but they displayed a strong insensitivity to inhibition by vanadate. An I170EGR/I275EGR double mutant was more significantly perturbed showing a reduced Vmax and pronounced vanadate insensitivity. The I170EGR site within the putative alpha-helical stalk region was cleaved to a maximum of 10% by factor Xa under non-denaturing conditions resulting in a characteristic 81 kDa fragment, whereas the I275EGR site, near the end of the beta-strand region, showed about 30-35% cleavage with the appearance of a 70 kDa fragment. A I170EGR/I275EGR double mutant enzyme showed about 55-60% cleavage. The cleavage profile for the mutant enzymes was enhanced under denaturing conditions, but was unaffected by MgATP or MgATP plus vanadate. Cleavage at the I275EGR position had no adverse effects on ATP hydrolysis or proton transport by the H(+)-ATPase making it unlikely that this localized region of LOOP1 influences coupling. Overall, these results suggest that the local region encompassing I275EGR is accessible to factor Xa, while the region around I170EGR appears buried. Although there is no evidence for gross molecular motion at either site, the effects of multiple amino acid substitutions in these regions suggest that the LOOP1 domain is conformationally active, and that perturbations in this domain affect the distribution of conformational intermediates during steady-state catalysis.

Amino Acid Sequence↗