Biomedical subjects

Wen Liu

Publications and source records attributed to Wen Liu.

99 records · Page 6Linked to original sources

PubMed2002

Effect of semi-synthesized quercetin water-soluble derivatives on recombinant human phosphatidylinositol 3-kinase p110beta catalytic subunit.

AIM: To study the effect of semi-synthesized quercetin water-soluble derivatives sodium quercetin-7-sulfate (SQMS) and disodium quercetin-7,4 -disulfate (SQDS) on recombinant human phosphatidylinositol 3-kinase (PI3-K) p110 beta catalytic subunit. METHODS: Recombinant human PI3-K p110 beta catalytic subunit was expressed by gene engineering. PI3 -K was assayed by incubating recombinant PI3-K p110beta with phosphatidylinositol-4,5-bisphosphate and [gamma-32P]ATP; the [32 P]-radiolabeled lipids were extracted with chloroform and methanol, assessed by thin layer chromatography and visualized by autoradiography. RESULTS: Wortmannin, a specific inhibitor o f PI3-K, showed inhibition on recombinant PI3-K p110beta catalytic subunit in a concentration-dependent manner (2.5 - 20 nmol/L); SQMS and SQD S showed inhibition on recombinant PI3-K p110beta catalytic subunit in a concentration-dependent manner (2.5 - 20 micromol/L). CONCLUSION: Semi-synthesized quercetin water-soluble derivatives were a type of inhibitors of PI3-K. The recombinant PI3-K p110beta catalytic subunit might be used as a molecular target for simpler filtrating and development of more effective inhibitors of PI3-K.

Androstadienes↗

PubMed2002

The effect of N-terminal changes on arginyl-tRNA synthetase from Escherichia coli.

An Asn(2) deleted mutant of Escherichia coli arginyl-tRNA synthetase deleted Asn(2) and a chimera mutant, in which the N-terminal 23 amino acid residues of yeast arginyl-tRNA synthetase were appended to the N-terminus of Escherichia coli synthetase, were synthesized and studied. The expression of the deletion and chimera mutants in Escherichia coli formed inclusion bodies, presumably due to improper folding of the proteins. Relative to the native enzyme, the deletion mutant showed full amino acid activation activity and a 26% reduction in aminoacylation activity, while the chimera mutant lost 93% and 96% activities in aminoacid activation and aminoacylation, respectively, and did not aminoacylate yeast tRNA(Arg) at all. The mutant deleted Asn(2) and Ile(3) was able to be expressed in Escherichia coli but not stable to be purified. The emission maximum wavelength in the fluorescence spectra of the chimera mutants shifted to longer one and the corresponding intensities decreased, when compared with those of the native enzyme. The data show that the conformation of the mutants are different and the tryptophan residues in the mutants are more exposed than those in the native enzyme. An estimate of the secondary structure of the mutant enzymes from their far ultraviolet CD spectra showed that the chimera mutant contained less alpha-helix, more beta-sheet and slightly higher fraction of random coil, as compared with the native enzyme. The results indicate that an intact N-terminal domain of E.coli arginyl-tRNA synthetase is important to its activity and correct folding.

Amino Acid Sequence↗

PubMed2002

[Inhibitory effect and kinetic analysis of sodium quercetin-7,4'-disulphate on recombinant human protein kinase CK2 holoenzyme].

AIM: To study the direct effect and kinetics of sodium quercetin-7,4'-disulphate (SQDS) on recombinant human protein kinase CK2 holoenzyme. METHODS: The recombinant human CK2 holoenzyme activity was assayed by detecting incorporation of 32P of [gamma-32P] ATP into the substrate in various conditions. RESULTS: The recombinant human CK2 was a second messenger (Ca2+, cAMP and cGMP) independent protein kinase. The characterization and function of the reconstituted holoenzyme were consistent with those of native CK2. SQDS was shown to strongly inhibit the holoenzyme activity of recombinant human protein kinase CK2 with an IC50 of 4.4 mumol.L-1, which was more effective than DRB and A3, known CK2 special inhibitors. Kinetic studies of SQDS on recombinant human CK2 showed: the inhibition was competitive with ATP and noncompetitive with casein. CONCLUSION: SQDS is a potent inhibitor of protein kinase CK2. This study provide experimental basis for the development of more effective inhibitors of CK2 and for clinical application of SQDS in the future.

Casein Kinase II↗

PubMed2002

[Synthesis and characterization of complex of Na2[Cu5(Shi)4].4H2O].

The complex, which is formed by reacting copper (II) with salicylhydroxamic acid (H3Shi), has been synthesized. The chemical formula of the complex was determined to be Na2[Cu5(Shi)4].4H2O by elemental analysis and spectrometric titration. The structure and the properties were tentatively investigated by using UV-Vis, IR, NMR, TG, fluorescence, molecular modeling and magnetic susceptibility measurement. The results show that the UV absorption peak corresponding to the pi-->pi* transition shifts towards red 25 nm, the d proton of salicylhydroxamic acid behaves as that of alkyl hydrocarbon in NMR and there is a strong magnetic interaction among the copper (II) ions in the complex.

Chelating Agents↗

PubMed2002

[Expression of vascular endothelial growth factor and its receptors (flt-1) in morbid human corneas and investigation of its clinic importance].

PURPOSE: To investigate the expression of vascular endothelial growth factor (VEGF) and its receptor (flt-1) in morbid corneas and the potential effects. METHODS: Eleven cases of normal peripheral corneas and limbal tissues and 32 cases of miscellaneous morbid corneas were collected during corneal transplantation. The specimens were sectioned in a cryostat and stained with streptavidin-biotin-peroxidase method for VEGF and flt-1. The expressive levels of VEGF were compared with grades of patients' clinical manifestations. RESULTS: Positive expression of VEGF was exclusively presented in all morbid corneal specimens and that of flt-1 was showed in most cases. Stronger staining was found in the epithelia and stoma of the morbid cornea. The expressive levels of VEGF were more important in the stroma and the endothelia of the morbid corneas than that in the normal peripheral corneas and were positively correlated with the degrees of corneal opacities and the area of corneal neovascularization in infiltrating inflammatory cells and proliferative tissues ( P < 0. 05). CONCLUSIONS: VEGF and flt-1 were expressed in miscellaneous morbid corneas and may play an important role in the repair of corneal injuries and the corneal neovascularization.

Cornea↗

PubMed1999

A Novel System for Hyper Expression and Rapid Purification of Arginyl-tRNA Synthetase from Escherichia coli.

The gene argS encoding arginyl-tRNA synthetase (ArgRS) in Escherichia coli has been cloned into the vector pMFT7-5 which allows overproduction of ArgRS. The specific activity of the synthetase in the crude extract of E.coli JM109(DE3) transformant containing the plasmid pMFT7-argS was approximately 2 500 times that of JM109(DE3) (the host strain without the vector). The overproduced synthetase can be purified to homogeneity with the specific activity of 36 000 units/mg under native condition within one day by a two-step purification system of DEAE-Sepharose CL-6B Fast Flow and Blue Sepharose CL-6B chromatographies with an overall yield of 69%. Moreover, this system makes it very easy to incorporate efficiently the expensive labeled amino acids into this enzyme. This novel system can conveniently provide a large amount of purified enzyme with a much higher specific activity than before which may be beneficial to NMR and crystallographic studies on this enzyme.

Journal Article↗

PubMed1999

Cellobiose Dehydrogenase Inhibition of Polymerization of Phenolic Compounds and Enhancing Lignin Degradation by Lignina.

The kinetic behavior of cellobiose dehydrogenase (CDH) was investigated by steady-state initial velocity studies. Variation in the concentration of one substrate led to changes in K(m) and V(max) of the other substrate. The results were consistent with a ping-pong mechanism. In the presence of cellobiose, CDH could reduce many oxidized products catalyzed by soybean hull peroxidase (SHP). The oxidation product of 1-hydroxybenzotriazole (HBT) catalyzed by SHP inactivated the enzyme itself however, CDH could prevent SHP from inactivation by reducing the oxidation product of HBT. CDH could also inhibit the polymerization of phenolic compounds catalyzed by SHP. It was found that the addition of CDH could enhance kraft pulp lignin degradation by ligninases.

Journal Article↗

PubMed1997

Total Synthesis of the Serine/Threonine-Specific Protein Phosphatase Inhibitor Tautomycin(1).

A convergent, asymmetric synthesis of the protein phosphatase inhibitor, tautomycin, is described. The natural product was constructed by joining two major fragments of comparable complexity at the C21-C22 bond. Absolute stereochemistry of the C1-C21 ketone originates from (S)-citronellene and (2R,3S)-geraniol epoxide. The anti stereochemical relationships at C6-C7 and C18-C19 were introduced with Duthaler's chiral titanium propionic enolate. Syn stereochemical relationships at C13-C14 and C23-C24 were established using an Evan's oxazolidinone chiral auxiliary. The spiroketal was efficiently constructed via a one-pot double-alkylation-spirocyclization sequence with acetone N,N-dimethylhydrazone serving as the central linchpin. Final coupling of the two halves using a chelation-controlled Mukaiyama aldol addition followed by deprotection yielded synthetic tautomycin that is identical to the natural product.

Journal Article↗

PubMedDate not supplied

Glucose deprivation induces mitochondrial dysfunction and oxidative stress in PC12 cell line.

Glucose metabolism plays a pivotal role in many physiological and pathological conditions. To investigate the effect of hypoglycemia (obtained by glucose deprivation) on PC12 cell line, we analyzed the cell viability, mitochondrial function (assessed by MTT reduction, cellular ATP level, mitochondrial transmembrane potential), and the level of reactive oxygen species (ROS) after glucose deprivation (GD). Upon exposure to GD, ROS level increased and MTT reduction decreased immediately, intracellular ATP level increased in the first 3 hours, followed by progressive decrease till the end of GD treatment, and the mitochondrial transmembrane potential (deltapsi(m)) dropped after 6 hours. Both necrosis and apoptosis occurred apparently after 24 hours which was determined by nuclei staining with propidium iodide(PI) and Hoechst 33342. These data suggested that cytotoxicity of GD is mainly due to ROS accumulation and ATP depletion in PC12 cells.

Adenosine Triphosphate↗