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Biomedical subjects

T Zhu

Publications and source records attributed to T Zhu.

At least 73 records · Page 4Linked to original sources
PubMed2000

Characterization of growth and acid formation in a Bacillus subtilis pyruvate kinase mutant.

Based on measurements and theoretical analyses, we identified deletion of pyruvate kinase (PYK) activity as a possible route for elimination of acid formation in Bacillus subtilis cultures grown on glucose minimal media. Evidence consistent with the attenuation of PYK flux has come from metabolic flux calculations, metabolic pool and enzymatic activity measurements, and a series of nuclear magnetic resonance experiments, all suggesting a nearly complete inhibition of PYK activity for glucose-citrate fed cultures in which the amount of acid formation was nearly zero. In this paper, we report the construction and characterization of a pyk mutant of B. subtilis. Our results demonstrate an almost complete elimination of acid production in cultures of the pyk mutant in glucose minimal medium. The substantial reduction in acid production is accompanied by increased CO(2) production and a reduced rate of growth. Metabolic analysis indicated a dramatic increase in intracellular pools of phosphoenolpyruvate (PEP) and glucose-6-P in the pyk mutant. The high concentrations of PEP and glucose-6-P could explain the decreased growth rate of the mutant. The substantial accumulation of PEP does not occur in Escherichia coli pyk mutants. The very high concentration of PEP which accumulates in the B. subtilis pyk mutant could be exploited for production of various aromatics.

Bacillus subtilis↗
PubMed2000

Role of protein phosphatases in the activation of CFTR (ABCC7) by genistein and bromotetramisole.

Genistein and bromotetramisole (Br-t) strongly activate cystic fibrosis transmembrane conductance regulator (CFTR; ABCC7) chloride channels on Chinese hamster ovary cells and human airway epithelial cells. We have examined the possible role of phosphatases in stimulation by these drugs using patch-clamp and biochemical methods. Genistein inhibited the spontaneous rundown of channel activity that occurs after membrane patches are excised from cAMP-stimulated cells but had no effect on purified protein phosphatase type 1 (PP1), PP2A, PP2B, PP2C, or endogenous phosphatases when assayed as [(32)P]PO(4) release from prelabeled casein, recombinant GST-R domain fusion protein, or immunoprecipitated full-length CFTR. Br-t also slowed rundown of CFTR channels, but, in marked contrast to genistein, it did inhibit all four protein phosphatases tested. Half-maximal inhibition of PP2A and PP2C was observed with 0.5 and 1.5 mM Br-t, respectively. Protein phosphatases were also sensitive to (+)-p-Br-t, a stereoisomer of Br-t that does not inhibit alkaline phosphatases. Br-t appeared to act exclusively through phosphatases since it did not affect CFTR channels in patches that had low apparent endogenous phosphatase activity (i.e., those lacking spontaneous rundown). We conclude that genistein and Br-t act through different mechanisms. Genistein stimulates CFTR without inhibiting phosphatases, whereas Br-t acts by inhibiting a membrane-associated protein phosphatase (probably PP2C) that presumably allows basal phosphorylation to accumulate.

Animals↗
PubMed2000

HIV-1 genotypes in peripheral blood monocytes.

CD4+ T cells and tissue macrophages are well defined as the major targets for human immunodeficiency virus type 1 (HIV-1) infection and replication, and their infection accounts for many aspects of HIV-1 pathogenesis in vivo. HIV-1 genotype and phenotype in monocytes and their potential roles in pathogenicity in vivo remain unknown. Herein is an overview of our initial work on HIV-1 genotype in purified CD14+ monocytes isolated longitudinally during the course of infection starting from the time of infection. Our data provide evidence for HIV-1 evolution in monocytes and their role as a reservoir of HIV-1 in vivo. A better understanding of HIV-1 in monocytes may greatly help the development of new therapeutic strategies for HIV-1 infection.

Amino Acid Sequence↗
PubMed2000

[Spectral characteristics of solar radiation in broadleaved Korean pine forest in Changbai Mountain].

Based on the measurement above and below forest canopy and meteorological data, the spectral characteristics of solar radiation in broadleaved Korean pine forest in Changbai Mountain was analyzed. The results show that the photosynthetically active radiation(PAP) coefficients of total radiation, direct radiation and scatter radiation changed daily and yearly, with an annual averages of 0.46, 0.43 and 0.56 respectively. The average reflectivity, transmissitvity and absorptivity of single leaves of different tree species in Korean pine forest were 27.0%, 23.4%, 49.6% respectively. Single leaves nearly absorbed all of the ultraviolet radiation(UV) and 71.8% of photosynthetically active radiation, but transmitted 9.6% and reflected 18.6%. As for near-infrared radiation (NIR), the reflectivity and transmissitivity of leaves were a little less than the absorptivity. The forest canopy absorbed 93.9% PAR and 94.1% UV, but reflected and transmitted less. It absorbed 59.2%, reflected 26.3% and transmitted 14.4% NIR.

Light↗
PubMed2000

[Wind tunnel experiment on canopy structural parameters of isolated tree and wind velocity field characters nearby].

The canopy structural parameters(porosity beta and permeability alpha) of isolated tree, and the wind velocity field character nearby were analyzed by wind tunnel experiment. The results show that alpha and beta fitted the function of alpha = beta 0.6, and the wind velocity nearby decreased in ellipsoid contour. The contour increased with increasing tree height and canopy width, and decreased with increasing permeability (or porosity). The isotach became the shape of ellipses or elliptic segments in horizontal and vertical plans.

Trees↗
PubMed2000

Calcitonin gene-related peptide in Langerhans cells in psoriatic plaque lesions.

OBJECTIVE: To study the mechanism of stress exacerbating psoriasis and the involvement effect of neuropeptides in psoriatic pathogenesis, we investigated the expression and secretion of calcitonin gene-related peptide (CGRP) in psoriatic lesions, then identified the target cells of CGRP, the characters of CGRP positive dendrite cells and the source of CGRP in psoriatic plaque lesions. METHODS: Specific radioimmunoassay (RIA) and immunohistochemistry staining methods were used to determine CGRP secretive content and the target cells of CGRP in psoriatic plaque lesion tissue of vulgaris psoriasis. Double immunofluorenscence staining was done on psoriatic plaque lesion sections by first using rabbit anti-human CGRP antibody and mouse anti-human CD1a antibody, second using PE-conjugated anti-mouse immunoglobulin and FITC-conjugated anti-rabbit immunoglobulin. Confocal laser microscope showed the psoriatic lesion sections. Then both digoxigenin labelled anti-sense and sense RNA probe of CGRP were synthesized to make sure the source of CGRP on the dendrite cells. The psoriatic lesion sections were studied by in situ hybridization. RESULTS: The content of CGRP in vulgaris psoriatic plaque lesions was higher than that of normal controls (P < 0.01). CGRP was also found on the dermal microvascular endothelial cells and the epidermal dendrite cells in psoriatic plague lesions. Further study showed that CGRP existed on the surface of epidermal CD1a + Langerhans cell in psoriatic plaque lesion. The CGRP mRNA expressed around the nucleus of the Langerhans cells in psoriatic lesion. CONCLUSIONS: The pathogenesis of psoriatic plaque lesions was closely related to the overexpression of neuropeptide CGRP. The CGRP contacted with the dermal microvascular endothelial cells and epidermal dendrite cells in psoriatic plaque lesion. The CGRP positive epidermal dendrite cell was CD1a + Langerhans cell. The Langerhans cell itself expressed CGRP mRNA.

Adult↗
PubMed2000

[Role of peroxynitrite on airway hyperresponsiveness in asthmatic guinea-pigs].

OBJECTIVE: To study the formation and localization of peroxynitrite(ONOO-) in the lung tissues of asthmatic guinea pig and investigate the effects of ONOO- on airway hyperresponsiveness in asthma. METHODS: 18 guinea pigs were randomly divided into three groups of 6 each: (1) asthmatic group: guinea pigs were injected intraperitoneally with 1 ml of 10% ovalbumin. After 14 days, the animals were exposed to aerosol of 1% OVA; (2) aminoguonidine (AG) group: Animal immunization was the same as above, but 1 h before the animals were exposed to OVA aerosol, 10 mg/kg AG were injected intraperitoneally. (3) control group. The formation and localization of ONOO- in the lung tissues of the guinea-pig asthma model were observed by immunohistochemical detection. The effect of exogenous ONOO- on contractions of isolated tracheal strips of the guinea-pigs to various concentrations of histamine was examined. The damage of airway epithelial cells induced by ONOO- was observed by electron microscopy. RESULTS: There was strong immunoreactivity for nitrotyrosine (NT), a specific marker of ONOO- formation in vivo, in the airway epithelial cells and inflammatory cells surrounding small airways of the guinea-pigs with asthma. The AG group showed significantly decreased number of NT positive cells in the lung tissues. There were only a few NT positive cells in the control group. The responsiveness of isolated tracheal strips to various concentration of histamine(except 10(-8) mol/L) in the ONOO- 0.5 mmol/L group were significantly increased compared with the vehicle group. (P < 0.05, P < 0.01 or P < 0.001). The sensitivity of isolated tracheal strips to histamine in the ONOO- 0.5 mmol/L group were also increased compared with the vehicle group(P < 0.001). Electron microscopical observation of the airways revealed airway epithelial injury and shedding. CONCLUSION: There was ONOO- overproduction in airway epithelial cells of asthmatic guinea-pigs, which may contribute to airway epithelial damage and hyperresponsiveness in asthma.

Animals↗
PubMed2000

[The selection of fluoroacetate-resistant mutant from E. coli MMR204 and its influence on the expression of heterologous GL-7ACA acylase].

In the cultivation of gene engineered strain of Escherichia coli on glucose medium, excretion and accumulation of acetic acid inhibit not only cell growth but also the the expression of heterologous protein. It is obvious that the desirable host strain maintaining acetate at a low level is one of the approaches to increase the production of recombinant protein. The present article deals with the selection of mutants of E. coli DP19, DP8, which grow on the medium containing pyruvate as the sole carbon source in the presence of 50 mmol/L fluoroacetic acid. It is shown that mutant DP19 is defective in its phosphotransacetylase(PTA) activity and accumulates less acetate in the medium, while DP8 is defective in acetate kinase (ACK) and accumulates similar level of acetate comparing with its parent. Using pta- mutant E. coli DP19 as host, the expression of GL-7ACA acylase gene on the recombinant plasmid pMR24 is improved, and the yield of enzyme activity in flask fermentation is about twice as much as its parent.

Acetate Kinase↗
PubMed1999

Association of cystic fibrosis transmembrane conductance regulator and protein phosphatase 2C.

Cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels are rapidly deactivated by a membrane-bound phosphatase activity. The efficiency of this regulation suggests CFTR and protein phosphatases may be associated within a regulatory complex. In this paper we test that possibility using co-immunoprecipitation and cross-linking experiments. A monoclonal anti-CFTR antibody co-precipitated type 2C protein phosphatase (PP2C) from baby hamster kidney cells stably expressing CFTR but did not co-precipitate PP1, PP2A, or PP2B. Conversely, a polyclonal anti-PP2C antibody co-precipitated CFTR from baby hamster kidney membrane extracts. Exposing baby hamster kidney cell lysates to dithiobis (sulfosuccinimidyl propionate) caused the cross-linking of histidine-tagged CFTR (CFTR(His10)) and PP2C into high molecular weight complexes that were isolated by chromatography on Ni(2+)-nitrilotriacetic acid-agarose. Chemical cross-linking was specific for PP2C, because PP1, PP2A, and PP2B did not co-purify with CFTR(His10) after dithiobis (sulfosuccinimidyl propionate) exposure. These results suggest CFTR and PP2C exist in a stable complex that facilitates regulation of the channel.

Animals↗
PubMed1999

Targeted manipulation of maize genes in vivo using chimeric RNA/DNA oligonucleotides.

Site-specific heritable mutations in maize genes were engineered by introducing chimeric RNA/DNA oligonucleotides. Two independent targets within the endogenous maize acetohydroxyacid synthase gene sequence were modified in a site-specific fashion, thereby conferring resistance to either imidazolinone or sulfonylurea herbicides. Similarly, an engineered green fluorescence protein transgene was site-specifically modified in vivo. Expression of the introduced inactive green fluorescence protein was restored, and plants containing the modified transgene were regenerated. Progeny analysis indicated Mendelian transmission of the converted transgene. The efficiency of gene conversion mediated by chimeric oligonucleotides in maize was estimated as 10(-4), which is 1-3 orders of magnitude higher than frequencies reported for gene targeting by homologous recombination in plants. The heritable changes in maize genes engineered by this approach create opportunities for basic studies of plant gene function and agricultural trait manipulation and also provide a system for studying mismatch repair mechanisms in maize.

Acetolactate Synthase↗
PubMed1999

Stoichiometry and kinetics of the high-affinity H+-coupled peptide transporter PepT2.

Proton-coupled peptide transporters mediate the absorption of a large variety of di- and tripeptides as well as peptide-like pharmacologically active compounds. We report a kinetic analysis of the rat kidney high-affinity peptide transporter PepT2 expressed in Xenopus oocytes. By use of simultaneous radioactive uptake and current measurements under voltage-clamp condition, the charge to substrate uptake ratio was found to be close to 2 for both D-Phe-L-Ala and D-Phe-L-Glu, indicating that the H+:substrate stoichiometry is 2:1 and 3:1 for neutral and anionic dipeptides, respectively. The higher stoichiometry for anionic peptides suggests that they are transported in the protonated form. For D-Phe-L-Lys, the charge:uptake ratio averaged 2.4 from pooled experiments, suggesting that Phe-Lys crosses the membrane via PepT2 either in its deprotonated (neutral) or its positively charged form, averaging a H+:Phe-Lys stoichiometry of 1.4:1. These findings led to the overall conclusion that PepT2 couples transport of one peptide molecule to two H+. This is in contrast to the low-affinity transporter PepT1 that couples transport of one peptide to one H+. Quinapril inhibited PepT2-mediated currents in presence or in absence of external substrates. Oocytes expressing PepT2 exhibited quinapril-sensitive outward currents. In the absence of external substrate, a quinapril-sensitive proton inward current (proton leak) was also observed which, together with the observed pH-dependent PepT2-specific presteady-state currents (Ipss), indicates that at least one H+ binds to the transporter prior to substrate. PepT2 exhibited Ipss in response to hyperpolarization at pH 6.5-8.0. However, contrary to previous observations on various transporters, 1) no significant currents were observed corresponding to voltage jumps returning from hyperpolarization, and 2) at reduced extracellular pH, no significant Ipss were observed in either direction. Together with observed lower substrate affinities and decreased PepT2-mediated currents at hyperpolarized Vm, our data are consistent with the concept that hyperpolarization exerts inactivation effects on the transporter which are enhanced by low pH. Our studies revealed distinct properties of PepT2, compared with PepT1 and other ion-coupled transporters.

Animals↗
PubMed1999

[The effect of upon the stimulating action of glyburide in the islet cell secretion of insulin and its mechanism].

OBJECTIVE: To study the effect and mechanism of amylin upon oral sulfonylurea drugs and its action to stimulate the islet cell secretion of insulin in rats. METHODS: Radioimmunogical and fluorescence methods were used to determine the amount of insulin secretion as well as the content of intracellular Ca(2+) of the rat islets incubated with amylin in different concentrations and followed by glyburide stimulation test. RESULTS: In amylin concentrations of 5 micromol/L and 10 micromol/L, 3 nmol/L glyburide decreased insulin release volume, being (3.8 +/- 1.0) microg/L and (2.1 +/- 1.0) microg/L as compare with (4.9 +/- 0.9) microg/L of the control group (t = 2.313, P < 0.05; t = 5.887, P < 0.01). Intracellular Ca(2+) content in the two concentrations was (270 +/- 15) nmol/L and (130 +/- 15) nmol/L, being markedly decreased as compared with (330 +/- 18) nmol/L of the control group. The changes were dosage related (t = 7.243, P < 0.01; t = 24.143, P < 0.01). CONCLUSION: High concentration of amylin is responsible for the prevention of the rise of Ca(2+) inside in the islet beta-cell acted upon by sulfonylurea drugs, this may be one of the mechanisms that bring about the decreased release of insulin.

Amyloid↗
PubMed1999

[The development of a bilateral groove lengthener].

A new series of bilateral groove external fixator are introduced in the article, which are mainly used to treat limb crispation. These apparatuses are composed of the groove frame threaded rod, hooked bolts, nuts and pins. They can be adjusted in several directions to correct the axis of limb in limb lengthening. The pins can be fixed on the anterior and posterior sides of the frame, with a stable angle structure. The devices are light and practical, with multiple functions, low price, simple and convenient operation. It can apply to all kinds of hospitals.

Bone Lengthening↗
PubMed1998

Growth hormone stimulates the formation of a multiprotein signaling complex involving p130(Cas) and CrkII. Resultant activation of c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK).

We have demonstrated previously that growth hormone (GH) activates focal adhesion kinase (FAK), and this activation results in the tyrosine phosphorylation of two FAK substrates, namely paxillin and tensin. We now show here in Chinese hamster ovary cells stably transfected with rat GH receptor cDNA that human (h)GH induces the formation of a large multiprotein signaling complex centered around another FAK-associated protein, p130(Cas) and the adaptor protein CrkII. hGH stimulates the tyrosine phosphorylation of both p130(Cas) and CrkII, their association, and the association of multiple other tyrosine-phosphorylated proteins to the complex. Both the c-Src and c-Fyn tyrosine kinases are tyrosine phosphorylated and activated by cellular hGH stimulation and form part of the multiprotein signaling complex as does tensin, paxillin, IRS-1, the p85 subunit of phosphatidylinositol 3-kinase, C3G, SHC, Grb-2, and Sos-1. c-Cbl and Nck are also tyrosine-phosphorylated by cellular stimulation with hGH and associate with the p130(Cas)-CrkII complex. c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) is activated in response to hGH in accordance with the formation of the abovementioned signaling complex, and hGH stimulated JNK/SAPK activity is increased in CrkII overexpressing NIH3T3 cells compared with vector transfected NIH3T3 cells. The formation of such a large multiprotein signaling complex by GH, with the resultant activation of multiple downstream effector molecules, may be central to many of the pleiotropic effects of GH.

3T3 Cells↗
PubMed1998

High affinity Ca2+ binding sites of calmodulin are critical for the regulation of myosin Ibeta motor function.

We coexpressed myosin Ibeta heavy chain with three different calmodulin mutants in which the two Ca2+-binding sites of the two N-terminal domain (E12Q), C-terminal domain (E34Q), or all four sites (E1234Q) are mutated in order to define the importance of these Ca2+ binding sites to the regulation of myosin Ibeta. The calmodulin mutated at the two Ca2+ binding sites in N-terminal domain and C-terminal domain lost its lower affinity Ca2+ binding site and higher affinity Ca2+ binding site, respectively. We found that, based upon the change in the actin-activated ATPase activities and actin translocating activities, myosin Ibeta with E12Q calmodulin has the regulatory characteristics similar to myosin Ibeta containing wild-type calmodulin, while myosin Ibeta with E34Q or E1234Q calmodulin lose all Ca2+ regulation. While the increase in myosin Ibeta ATPase activity paralleled the dissociation of 1 mol of calmodulin from myosin Ibeta heavy chain for both wild type (above pCa 5) and E12Q calmodulin (above pCa 6), the Ca2+ level required for the inhibition of actin-translocating activity of myosin Ibeta was lower than that required for dissociation of calmodulin, suggesting that the conformational change induced by the binding of Ca2+ at the high affinity site but not the dissociation of calmodulin is critical for the inhibition of the motor activity. Our results suggest that the regulation of unconventional myosins by Ca2+ is directly mediated by the Ca2+ binding to calmodulin, and that the C-terminal pair of Ca2+-binding sites are critical for this regulation.

Actins↗
PubMed1998

Growth hormone stimulates the tyrosine phosphorylation and association of p125 focal adhesion kinase (FAK) with JAK2. Fak is not required for stat-mediated transcription.

We have demonstrated that growth hormone (GH) activates focal adhesion kinase (FAK), and this activation results in the tyrosine phosphorylation of two FAK substrates, paxillin and tensin. The activation of FAK is time-dependent (maximal activation at 5-15 min) and dose-dependent (maximal activation at 0.05 nM). FAK and paxillin are constitutively associated in the unstimulated state, remain associated during the stimulation phase, and recruit tyrosine-phosphorylated tensin to the complex after GH stimulation. Half of the carboxyl-terminal region of the GH receptor is dispensable for FAK activation, but FAK activation does require the proline-rich box 1 region of the GH receptor, indicative that FAK is downstream of JAK2. FAK associates with JAK2 but not JAK1 after GH stimulation of cells. Using FAK-replete and FAK-deficient cells, we also show that FAK is not required for STAT-mediated transcriptional activation by GH. The use of FAK in the signal transduction pathway utilized by GH may be central to many of the pleiotropic effects of GH, including cytoskeletal reorganization, cell migration, chemotaxis, mitogenesis, and/or prevention of apoptosis and gene transcription.

Animals↗