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L X Xu

Publications and source records attributed to L X Xu.

At least 55 records · Page 3Linked to original sources
PubMed1991

Gap junctions formed by connexins 26 and 32 alone and in combination are differently affected by applied voltage.

Gap junctions are formed by a family of homologous proteins termed connexins. Their channels are dodecamers, and homomeric forms differ in their properties with respect to control by voltage and other gating stimuli. We report here the properties of coupling from expression of connexin complementary RNAs (cRNAs; sense to mRNA, antisense to cDNA) in Xenopus oocyte pairs in which endogenous coupling was blocked by injection of DNA oligonucleotides antisense to the mRNA of Cx38, the principal endogenous connexin. We found that a connexin recently sequenced from rat liver, Cx26, formed functional gap junctions whose conductance exhibited voltage dependence with unusual characteristics suggestive of two gating mechanisms. Junctional conductance (gj) was increased to a small degree by depolarization and decreased by hyperpolarization of either cell in a coupled pair, indicating dependence on the potential between the inside and outside of the cells (Vi-o). These changes were fast compared with the resolution of their measurement (ca. 10 ms). On a slower timescale, large transjunctional potentials (Vj) of either sign caused a more substantial decrease in conductance similar to that previously reported for several other gap junctions. Homotypic junctions formed of another connexin, Cx32, exhibited a similar slow dependence on Vj but no dependence on Vi-o. In contrast, heterotypic junctions between an oocyte expressing Cx26 and one expressing Cx32 were electrically asymmetric; they exhibited a greater fast change in gj, which depended, however, on Vj, such that gj increased with relative positivity on the Cx26 side and decreased with relative negativity on the Cx26 side. There was also a large slow decrease in gj in response to Vj for relative positivity on the Cx26 side but not for Vj of the opposite sign. These data indicate that properties of the hemichannels contributed by the two connexins in the heterotypic case were changed from their properties in homotypic junctions. The fast change in gj may involve a mechanism analogous to that at fast rectifying electrical synapses. Experiments in which oocytes expressing Cx32 were paired with oocytes expressing both Cx26 and Cx32 demonstrated that asymmetric junctions would form between oocytes expressing both connexins, thereby confirming their potential relevance in vivo, where the same coupled cells are known to express both proteins.

Animals↗
PubMed1991

Transcription from the adenovirus major late promoter uses redundant activating elements.

The adenovirus major late promoter (MLP) has been analyzed by constructing recombinant viral genomes containing mutations in possible promoter elements. Single base pair changes in the TATA box had no effect on viral replication, and MLP expression, as measured by the accumulation of late mRNAs, was at wild type levels. However, a double mutation in the TATA box reduced viral replication and MLP expression, demonstrating that the TATA box is important, although not essential, for maximal activity in virus. Primer extension analysis showed that the mRNAs were initiated at the correct position. A mutation in the CAAT box was viable, and had only minor effects on MLP expression. However, this mutation when coupled to a single mutation in the TATA box, severely reduced viral replication and expression from the MLP. Similarly, a viable mutation in the UPE, shown previously to abolish binding of USF, coupled to a single mutation in the TATA box was lethal. These results suggest that both USF and the CAAT box binding factor CP1 can interact with TFIID to effect activation, and thus that the mechanism of activation is functionally redundant.

Adenoviridae↗
PubMed1991

Determination of taxol in Taxus chinensis by HPLC method.

A method for the determination of taxol in Taxus chinensis by HPLC method using betamethasone as internal standard is described. The column employed was packed with 10 microns silica gel YWG 80 (250 x 4 mm), the eluting solvent consisted of CH2Cl2--MeOH (95:5) and the effluent was monitored at 228 nm. The coefficients of variation are less than 2%.

Alkaloids↗
PubMed1990

Association of polycystic kidney disease and an HLA haplotype within a family clan.

Nine members of a Chinese family underwent for HLA-A, -B. and -DR typing using microlymphocytotoxicity technique. The results of genotyping of the family showed that all four individuals who suffered from polycystic kidney disease shared the HLA-A9(Aw24), -Bw22, and -DR5 haplotype. It indicated that polycystic kidney disease was associated with an HLA haplotype in the family. We suggested that the HLA-A9(Aw24), -Bw22, -DR5 chromosome might carry the susceptibility gene of polycystic kidney disease in this family.

Adult↗
PubMed1990

[Determination of ranunculin in Pulsatilla chinensis and synthetic ranunculin by reversed phase HPLC].

A method for the determination of ranunculin in Pulsatilla chinensis and synthetic ranunculin by reversed phase HPLC using betamethasone as internal standard is described. The column employed was a 10 micron LiChrosorb RP-18 (230 x 14 mm), the eluting solvent consisted of methanol-water (40:10, V/V) and the effluent was monitored at 225 nm. The advantages of this method are simple, rapid and accurate. The coefficients of variation are less than 1%.

Anti-Infective Agents↗
PubMed1989

[Determination of bile acids in bear gall drainage by thin layer chromatographic scanning].

A method for the quantitative determination of three main bile acids, cholic acid (CA), ursodesoxycholic acid (UDCA) and chenodesoxycholic acid (CDCA), in bear gall, drainage from bear gall and bear gallstone is described. Experimental conditions: TLC Scanner CS-910, fluorescence scanning, lambda ex 470 nm and lambda em 550 nm for CA; lambda ex 380 nm and lambda em 450 nm for UDCA and CDCA. The results showed that the contents of UDCA and CDCA in bear gall drainage were higher than those in bear gall. The method is simple, rapid and sensitive. The reproducibility is good. The average recovery is 98.4%, CV is 1.4%.

Animals↗
PubMed1989

Coulometric titration of total flavonoids in Sophora japonica L.

A method for the determination of total flavonoids in Sophora japonica L. by coulometric titration was developed. The titration was carried out in a mixture of 1 mol/L KBr--2 mol/L HCl (1:1) and bromine was generated at the anode, rutin reacted with two moles of bromine with an n value of 4. The advantages of this method are simple and rapid, it can be used to analyze small amount of sample.

Drugs, Chinese Herbal↗
PubMed1989

Determination of total flavonoids in Epimedium brevicornum maxim by differential pulse polarography.

The polarographic behavior of icariin in various electrolytes was studied. It was found that a well defined peak was obtained in 0.05 mol/L ammonium sulfate supporting electrolyte at a potential of -1.51 V (vs Ag/AgCl). An excellent linear relationship was obtained between the concentration (1.28-3.85 X 10(-6) mol/L) and peak current. The method can be used to analyze flavonoids in small amount of medicinal herb samples.

Drugs, Chinese Herbal↗
PubMed1986

Investigations of primary and secondary structure of porcine ubiquitin. Its N epsilon-acetylated lysine derivative.

N epsilon-acetylation in vitro of internal lysyl residues of Ub by p-nitro-phenyl acetate at pH 8.0 was performed. The position of acetylation sites are determined. (e.g. Fully acetylated: Lys-6, Lys-11 and Lys-33; partially free internal lysines: Lys-27, Lys-29; Lys-48 and probably Lys-63.) 55 cycles Edman degradation were performed and the first 53 N-terminal residues were identified. Secondary structural studies of ubiquitin have been carried out using the circular dichroism (CD) technique. No changes are noted upon heating to 100 degrees C at neutral pH even in the presence of 8 M urea but in 6 M guanidine-HCl extensive modification results. Ubiquitin with an average of 4.4 of its 7 lysines in the N epsilon-acetyl form shows little deviation from native protein. After reduction with dithiothreitol and subsequent removal of the mercaptan, significant changes in the secondary structure are noted. Circular dichroic measurements of ubiquitin indicated an alpha-helical content of about 10% whereas the secondary structural predictions of Chou and Fasman suggest a level of about 45%.

Acetylation↗
PubMed1985

N-epsilon-acetylation of porcine mature erythrocytes ubiquitin.

Highly purified of porcine mature erythrocytes ubiquitin were obtained according to the experimental procedure reported by Jabusch and Deutsch (1983). N-epsilon-acetylation in vitro of internal lysyl residues of ubiquitin by p-nitro-phenyl-acetate at pH 8.0 was performed. The extent of acetylation of ubiquitin was determined: about 4-5 residues (4.5 residues) of N-epsilon-lysine groups of ubiquitin were acetylated. We have assigned by Edman degradation the sites of acetylation and the sites of remaining free internal N-epsilon-lysine residues in the sequence: fully acetylated: Lys-6, Lys-11 and Lys-33. Partially free N-epsilon-lysine: Lys-27 and Lys-29 and probably Lys-48 and Lys-63. 50 cycles Edman degradation were performed on porcine ubiquitin and the first 45 N-terminal residues were identified. We have partially determined that the molecular conservation of 45 amino acid sequence of ubiquitin between cattle, man and swine since the 45 amino acid sequence out of 76 residues are identical. The amino acid composition between human and porcine ubiquitin are also identical.

Acetylation↗