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Biomedical subjects

Z Wu

Publications and source records attributed to Z Wu.

At least 595 records · Page 33Linked to original sources
PubMed1996

[The features of color pattern electroretinogram in early primary open-angle glaucoma].

OBJECTIVE: To observe the features of the changes of color pattern electroretinogram (CP-ERG) in early primary open-angle glaucoma (POAG). METHOD: The detection and analyses of CP-ERGs in 29 patients (48 eyes) with POAG, 10 patients (16 eyes) with ocular hypertension and 33 age-matched normal volunteers (48 eyes) were made. RESULTS: The changes of CP-ERG in early POAG included reduction of amplitudes of P1 and N2 waves, prolongation of the peak times of red/black N2 and blue/black P1 waves. Part of the patients with ocular hypertension had the amplitude of N2 wave reduced. Five factors including the amplitude of blue/black N2 wave, the amplitudes of red/black P1 and N2 waves, the peak time of red/black N2 wave and the white/black P1 to N2 wave amplitude ratio from CP-ERG which are significantly correlated to the diagnosis of early POAG were selected by the multiple factor stepwise discriminatory analysis, and the stepwise discriminatory function was set up. CONCLUSIONS: CP-ERG is a useful method in detecting the retinal functions in early POAG, and is helpful to its early diagnosis.

Adult↗
PubMed1996

[Electrophoretic determination of aqueous and serum neuron-specific enolase (NSE) in the diagnosis of retinoblastoma].

OBJECTIVE: Neuron-specific enolase (NSE) or isoenzymes containing gamma-enolase are considered valuable in the diagnosis of tumors of neuroectodermal origin. METHOD: We used rapid electrophoretic method on cellulose acetate plate to determine the patterns of enolase isoenzymes in the 21 aqueous humor and 23 serum specimens from 23 patients with retinoblastoma (Rb) and 21 aqueous and 25 serum specimens from 25 control cases to evaluate NSE in the diagnosis of RB. The assay allowed assessment of all three major isoenzymes (alpha alpha, alpha gamma, and gamma gamma), and NSE relative activity and its percentage in the total relative activity of the three enolase isoenzymes were assessed by means of a fluorometer. RESULTS: Aqueous from all patients with Rb contained alpha alpha, alpha gamma, and gamma gamma isoenzymes and presented strong positive, the positive rate of NSE being 100% and its relative activity accounting for 45 +/- 9% of the total relative activity of the 3 enolase isoenzymes; no enolase was detectable in the control aqueous with cataract, glaucoma and Coats's diseases (4 cases), but in two patients with traumatic hyphema alpha alpha band, while the sera faint alpha gamma and gamma gamma presented in the aqueous. The control serum contained only an alpha alpha band, while the sera from patients with RB contained alpha alpha, alpha gamma and gamma gamma bands in 18 of 23 specimens, the positive rate being 78.2%, and only alpha alpha bands in the rest 5 specimens (21.8%). In the patients with Rb, the NSE relative activity and its percentage in the total relative activity of the 3 isoenzymes in serum (36 +/- 9%) were significantly lower than that in aqueous. CONCLUSION: The amounts of NSE significantly in both serum and aqueous from patients with Rb, and the immunoelectrophoretic assay for determination of enolase patterns is valuable in the diagnosis and differential diagnosis of Rb. In addition, the method is rapid, simple and requires only a little among (< 5 microliters) of sample.

Aqueous Humor↗
PubMed1996

[Effect of fibronectin on the synthesis of extracellular matrix proteins in periodontal ligament cells].

Immunofluorescence staining method and fluorescence spectrophotometry were used to study the synthesis of extracellular matrix proteins in periodontal ligament cells (PDL cells) when exogenous fibronectin (FN) existed. The results showed that the right amount of exogenous FN (0.044 mumol/l) could increase the amount of type I collagen and type III collagen in PDL cells (P < 0.01), inhibit the synthesis of FN itself (P < 0.01). It suggested that exogenous FN can effect the synthesis of extracellular matrix proteins so as to promote a new connective tissue attachment formation.

Adolescent↗
PubMed1996

[The effect of mitomycin C on activities of carbonic anhydrase and ATPase of the ciliary body epithelium in rabbit].

PURPOSE: Enzymohistochemical methods were performed to observe the effect of mitomycin C(MMC) on the activities of carbonic anhydrase (CA) and ATPase of the ciliary body epithelium in rabbits after using 0.2mg/ml mitomycin C during sclerectomy for the further study on the mechanism of the decrease of intraocular pressure postoperatively. METHODS: 0.2mg/ml mitomycin C was topically applicated during the sclerectomy in rabbit eyes. 7 days postoperatively, Hasson's method and plumbum nitrate's method were used to stain the CA and ATPase of the ciliary body epithelium. The grey value of the enzymes was quantitated by Image Analysor. RESULTS: MMC inhibited the activities of CA and ATPase of the ciliary body epithelium underlying the site of MMC application, but the difference of enzymatic activities of the region 90 degree apart from the surgical site and that of surgical site in normal saline control group was not statistically obvious (P < 0.05). CONCLUSIONS: MMC could inhibit the activities of CA and ATPase of ciliary body epithelium, thus leading to the decreased secretion of humor aqueous and the lowerdown of intraocular pressure even persistent hypotony.

Adenosine Triphosphatases↗
PubMed1996

[Assessment of the toxicity of TAH on the cell lines of SO-Rb50 and SO-Rb70].

PURPOSE: MTT assay was evaluated on cytoxicity for suspension growing cell lines of SO-Rb50 and SO-Rb70, and the toxicity of TAH (the total alkaloid of peqanum harmala L) on the above cell lines was assessed. METHODS: The relationships between cell number and optical density, between optical density and exposure time of MTT, and the stability of formazan crystal solution in MDSO were determined. And the toxicity of TAH on the cell lines of SO-Rb50 and SO-Rb70 in vitro with MTT assay was assessed. RESULTS: There was a direct proportional relationship between the amount of cell number and its optical density; The optical density increased gradully within 12 hours of the MTT incubation time; The stable time of the formazan crystal solved in DMSO was 11 hours. The IC50 values (micrograms/ml) of TAH on SO-Rb50 were 10.66, 4.82 respectively for 48 and 72 hours; and on SO-Rb70 were 6.38, 4.2 respectively for 48 and 72 hours. CONCLUSION: MTT assay can be used for suspension growing cell lines of SO-Rb50 and SO-Rb70: TAH has obvious toxicity to these two cell lines.

Alkaloids↗
PubMed1996

Some design recommendations to improve comfort in helmets: a case study from China.

Unless the basic user needs are satisfied in safety helmets, it is difficult to get workers to wear them habitually and for long periods. Hotness, weight and fitting problems are major wearability issues that require improvements. The enormous need for an optimally designed helmet in China prompted a case study on comfort aspects in helmets. The subjective impressions of the wearers of test helmets provided useful information for design changes to improve comfort. The heat transfer measurements through helmets indicated the need for ventilation openings to be provided on the shell of plastic helmets. Due to the advantage of low weight and good ventilation, it is recommended that cane helmets be further developed to improve protection, wearability and durability, and subsequently be produced in large scale.

Adult↗
PubMed1995

Phosphinate analogs of D-, D-dipeptides: slow-binding inhibition and proteolysis protection of VanX, a D-, D-dipeptidase required for vancomycin resistance in Enterococcus faecium.

VanX is a D-Ala-D-Ala dipeptidase that is essential for vancomycin resistance in Enterococcus faecium. Contrary to most proteases and peptidases, it prefers to hydrolyze the amino substrate but not the related kinetically and thermodynamically more favorable ester substrate D-Ala-D-lactate. The enzymatic activity of VanX was previously found to be inhibited by the phosphinate analogs of the proposed tetrahedral intermediate for hydrolysis of D-Ala-D-Ala. Here we report that such phosphinates are slow-binding inhibitors. D-3-[(1-Aminoethyl)phosphinyl]-D-2-methylpropionic acid I showed a time-dependent onset of inhibition of VanX and a time-dependent return to uninhibited steady-state rates upon dilution of the enzyme/inhibitor mixture. The initial inhibition constant Ki after immediate addition of VanX to phosphinate I to form the E-I complex is 1.5 microM but is then lowered by a relatively slow isomerization step to a second complex, E-I*, with a final K*i of 0.47 microM. This slow-binding inhibition reflects a Km/K*i ratio of 2900:1. The rate constant for the slow dissociation of complex E-I* is 0.24 min-1. A phosphinate analog with an ethyl group replacing what would be the side chain of the second D-alanyl residue in the normal tetrahedral adduct gives a K*i value of 90 nM. Partial proteolysis of VanX reveals two protease-sensitive loop regions that are protected by the intermediate analog phosphinate, indicating that they may be part of the VanX active site.

Bacterial Proteins↗
PubMed1995

Conditional ectopic expression of C/EBP beta in NIH-3T3 cells induces PPAR gamma and stimulates adipogenesis.

Activation of adipogenesis in 3T3 preadipocytes by exposure to the adipogenic inducers dexamethasone, methylisobutylxanthine, insulin, and fetal bovine serum is accompanied by a transient burst of C/EBP beta protein expression that precedes the induction of the fat gene program. In this study we have investigated the role of C/EBP beta in initiating the adipogenic program by overexpressing C/EBP beta in multipotential NIH-3T3 fibroblasts. Conditional ectopic expression of C/EBP beta was accomplished by using an artificial transcriptional regulatory system based on the Escherichia coli tetracycline repressor to generate a stable cell line, beta 2, that expresses C/EBP beta mRNA and protein in a tightly controlled tetracycline dose-dependent manner. Induction of C/EBP beta DNA-binding activity in NIH-3T3 beta 2 cells exposed to dexamethasone in the presence of insulin and fetal bovine serum activates the expression of an adipocyte-specific nuclear hormone receptor, PPAR gamma, that stimulates the conversion of these fibroblasts into committed preadipocytes. Either ectopic expression of C/EBP beta or treatment with dexamethasone alone is incapable of inducing PPAR gamma expression, but when present together, they have a synergistic effect on the adipogenic program. Exposure of these stimulated cells to a PPAR activator 5,8,11,14-eicosatetraynoic acid (ETYA) results in the accumulation of fat droplets and expression of the adipocyte-enriched genes aP2 and glycerol phosphate dehydrogenase (GPD). The number of beta 2 cells that can differentiate into adipocytes is related to the concentration of tetracycline and, therefore, the amount of the exogenous C/EBP beta protein expressed. C/EBP beta can induce PPAR gamma mRNA in the absence of ETYA; however, expression of aP2 mRNA and maximum fat deposition is dependent on the PPAR activator. Our results suggest that enhanced expression of C/EBP beta converts multipotential mesenchymal precursor cells into preadipocytes that respond to adipogenic inducers, including dexamethasone and PPAR activators to differentiate into adipocytes.

1-Methyl-3-isobutylxanthine↗
PubMed1995

A novel DNA binding and nuclease activity in domain III of Mu transposase: evidence for a catalytic region involved in donor cleavage.

The Mu A protein is a 75 kDa transposase organized into three structural domains. By severing the C-terminal region (domain III) from the remainder of the protein, we unmasked a novel non-specific DNA binding and nuclease activity in this region. Deletion analysis localized both activities to a 26 amino acid stretch (aa 575-600) which remarkably remained active in DNA binding and cleavage. The two activities were shown to be tightly linked by site-directed mutagenesis. To study the importance of these activities in the transposition process, an intact mutant transposase lacking the DNA binding and nuclease activity of domain III was constructed and purified. The mutant transposase was indistinguishable from wild-type Mu A in binding affinity for both the Mu ends and the enhancer, and in strand transfer activity when the cleavage step was bypassed. In contrast, the mutant transposase displayed defects in both synapsis and donor cleavage. Our results strongly suggest that the 26 amino acid region in domain III carries catalytic residues required for donor DNA cleavage by Mu A protein. Furthermore, our data suggest that an active site for donor cleavage activity in the Mu tetramer is assembled from domain II (metal ion binding) in one A monomer and domain III (DNA cleavage) in a separate A monomer. This proposal for active site assembly is in agreement with the recently proposed domain sharing model by Yang et al. (Yang, J.Y., Kim, K., Jayaram, M. and Harshey, R.M. [1995] EMBO J., 14, 2374-2384).

Amino Acid Sequence↗
PubMed1995

Solution assembly of a soluble, heteromeric, high affinity interleukin-2 receptor complex.

In this study, we report the use of coiled-coil (leucine zipper) molecular recognition for the solution assembly of stable, high affinity, heteromeric interleukin-2 receptor complexes. Co-expression of interleukin-2 receptor alpha and beta extracellular domains (ectodomains), each fused to seven coiled-coil heptad repeats, resulted in the formation of heteromeric complexes that bound interleukin-2 in a cooperative fashion and with much higher affinity than similar homomeric complexes. The dissociation constants for these solution complexes are within the range of values reported for the comparable cell surface "pseudo high affinity" interleukin-2 receptor. Ligand-induced cross-linking of homomeric or heteromeric receptor subunits is the common signal transmission mechanism employed by hematopoietin receptors. Individual receptor ectodomains, however, often do not bind ligand with measurable affinity. This is the first study to demonstrate the feasibility of coiled-coil mediated preassembly of cytokine receptor complexes.

Allosteric Regulation↗
PubMed1995

Ligand binding analysis of soluble interleukin-2 receptor complexes by surface plasmon resonance.

Knowledge of the kinetic binding characteristics is often critical to the development of ligand/receptor structure-activity relationships. To better understand the contribution of each of the subunits to ligand binding in the multimeric interleukin-2 receptor system, we have previously prepared stable solution complexes of the alpha- and beta-subunits. In this study, we have employed surface plasmon resonance biosensor methodology (BIAcore) to evaluate both the kinetic and equilibrium binding constants for these complexes. The structural nature of the complexes facilitated immobilization on the sensor surfaces in a manner that minimized interference with ligand interactions. The interleukin-2 receptor complex surfaces displayed excellent binding capacity and stability toward regeneration. In all cases where the binding constants were measurable, the values determined for interleukin-2 were in good agreement with those previously determined by other methods. When interleukin-2 analogs with receptor subunit specific mutations were employed, the binding parameters were consistent with the nature of the mutations. The combination of coiled-coil-mediated solution assembly and surface plasmon resonance analysis of ligand binding provides a powerful approach to the study of multimeric cytokine receptor systems.

Artifacts↗
PubMed1995

Voltage-sensitive adenylyl cyclase activity in cultured neurons. A calcium-independent phenomenon.

Catalytic subunits of mammalian adenylyl cyclases have been proposed to contain 12 transmembrane domains, a property shared with some voltage-sensitive ion channels. Here we report that adenylyl cyclase activity in cerebellar neurons is synergistically stimulated by depolarizing agents and beta-adrenergic receptor activation. This phenomenon is Ca(2+)-independent and not attributable to Ca(2+)-stimulated adenylyl cyclase activity. Cholera toxin and forskolin also synergistically stimulate adenylyl cyclase activity in combination with depolarizing agents. We hypothesize that conformational changes in the catalytic subunit of the enzymes caused by changes in the membrane potential may enhance stimulation of adenylyl cyclases by the guanylyl nucleotide stimulatory protein. This novel mechanism for regulation of adenylyl cyclases generates robust cAMP signals that may contribute to various neuromodulatory events including some forms of neuroplasticity.

Adenylyl Cyclases↗
PubMed1995

Developmentally expressed Ca(2+)-sensitive adenylyl cyclase activity is disrupted in the brains of type I adenylyl cyclase mutant mice.

The type I Ca(2+)-sensitive adenylyl cyclase has been implicated in several forms of synaptic plasticity in vertebrates. Mutant mice in which this enzyme was inactivated by targeted mutagenesis show deficient spatial memory and altered long term potentiation (Wu, Z. L., Thomas, S. A., Villacres, E. C., Xia, Z., Simmons, M. L., Chavkin, C., Palmiter, R. D., and Storm, D. R. (1995) Proc. Natl Acad Sci. U. S. A. 92, 220-224). Long term potentiation in the CA1 region of the rat hippocampus develops during the first 2 weeks after birth and reaches maximal expression at postnatal day 15 with a gradual decline at later stages of development. Here we report that Ca(2+)-stimulated adenylyl cyclase activity in rat hippocampus, cerebellum, and cortex increases significantly between postnatal days 1-16. This increase appears to be due to enhanced expression of type I adenylyl cyclase rather than type VIII adenylyl cyclase, the other adenylyl cyclase that is directly stimulated by Ca2+ and calmodulin. Type I adenylyl cyclase mRNA in the hippocampus increased 7-fold during this developmental period. The developmental expression of Ca(2+)-stimulated adenylyl cyclase activity in mouse brain was attenuated in mutant mice lacking type I adenylyl cyclase. Changes in expression of the type I adenylyl cyclase during the period of long term potentiation development are consistent with the hypothesis that this enzyme is important for neuroplasticity and spatial memory in vertebrates.

Adenylyl Cyclases↗
PubMed1995

Ligand binding analysis of interleukin-2 receptor complexes using surface plasmon resonance.

In this study we have employed surface plasmon resonance to examine the kinetic binding constants of a new class of soluble cytokine receptor complexes. The solution assembly of both homomeric and heteromeric interleukin-2 receptor ectodomain complexes has been achieved using coiled-coil molecular recognition. These complexes were immobilized on a biosensor surface and the kinetic binding constants were determined. The values obtained for these parameters compared favorably with those reported in studies of comparable cell surface complexes. The combination of these methods provides a powerful approach to the ligand interactions of cytokine receptors.

Antigen-Antibody Complex↗
PubMed1995

Protein-peptide interactions analyzed with the yeast two-hybrid system.

The yeast two-hybrid system was used to screen a library of random peptides fused to a transcriptional activation domain in order to identify peptides capable of binding to the retinoblastoma protein (Rb). Seven peptides were identified, all of which contain the Leu-X-Cys-X-Glu motif found in Rb-binding proteins, although their activity in the yeast assay varied over a 40-fold range. Mutagenesis of the DNA encoding two of these peptides followed by screening in the two-hybrid system allowed the delineation of residues apart from the invariant Leu, Cys and Glu that affect binding to Rb. Binding affinities of a peptide and one of its variants to Rb, determined by surface plasmon resonance, correlated with results from the two-hybrid assay. This method offers several advantageous features compared to existing technology for screening peptide libraries: in vivo detection of protein-peptide interactions, high sensitivity, the capacity for rapid genetic screening to identify stronger and weaker binding peptide variants, and the use of a simple assay (transcriptional activity) as a means to assess binding affinity.

Amino Acid Sequence↗
PubMed1995

Covalent sequestration of melphalan by metallothionein and selective alkylation of cysteines.

Rabbit liver metallothionein-2 is shown to form covalent bonds with the anticancer agent melphalan, in support of the hypothesis that covalent sequestration by metallothionein constitutes one mechanism for the cross-resistance acquired by cancer patients to therapeutic alkylating agents. Among 20 cysteines in the 2-domain protein, 89% of the first alkylation reaction occurs with 2 that cochelate a zinc cation in the carboxy domain. Computer-supported docking studies indicate a favorable binding site for melphalan near these cysteine sulfhydryl groups. Although folded metallothionein-2 is resistant to trypsin cleavage, alkylation by 1 mol of melphalan allows cleavage by trypsin between the two globular domains.

Alkylation↗
PubMed1995

Overexpression, purification, and characterization of VanX, a D-, D-dipeptidase which is essential for vancomycin resistance in Enterococcus faecium BM4147.

Vancomycin resistance in Enterococcus faecium requires five genes: vanR, vanS, vanH, vanA, and vanX. The functions and mechanism of four gene products have been known, with VanR/S for signal transduction and transcriptional regulation and VanH/A to synthesize D-Ala-D-lactate. But the function of the fifth gene product, VanX, has been unknown until very recently, when Reynolds and colleagues discovered D-, D-dipeptidase activity in crude extracts of a VanX overproducer [Reynolds, P. E., et al. (1994) Mol. Microbiol. 13, 1065-1070]. We report here the expression of VanX in Escherichia coli and its purification to homogeneity. VanX has been characterized as a metal-activated D-, D-dipeptidase with an optimal pH range of 7-9. The kcat and Km of D-Ala-D-Ala in the absence of divalent metal are determined to be 4.7 s-1 and 1 mM, respectively. However, in the presence of metal cations, kcat can be as high as 788 s-1. VanX is unable to hydrolyze D-Ala-D-lactate, the substituted moiety in the peptidoglycan that leads to vancomycin resistance, not only because of low binding affinity (Ki estimated at 242 mM) but also due to a kcat less than 0.005 s-1. The more than 10(5)-fold differential in catalytic efficiency of VanX for hydrolysis of D-Ala-D-Ala vs D-Ala-D-lactate leaves D-Ala-D-lactate intact for subsequent incorporation into peptidoglycan.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗