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Biomedical subjects

T Xiang

Publications and source records attributed to T Xiang.

At least 19 recordsLinked to original sources
PubMed2003

Effects of the Dzyaloshinskii-Moriya interaction on low-energy magnetic excitations in copper benzoate.

We have investigated the physical effects of the Dzyaloshinskii-Moriya (DM) interaction in copper benzoate. In the low-field limit, the spin gap is found to vary as H(2/3)ln((1/6)(J/mu(B)H(s)) (H(s): an effective staggered field induced by the external field H) in agreement with the prediction of conformal field theory, while the staggered magnetization varies as H(1/3) and the ln((1/3)(J/mu(B)H(s)) correction predicted by conformal field theory is not confirmed. The linear scaling relation between the momentum shift and the magnetization is broken. We have determined the coupling constant of the DM interaction and have given a complete quantitative account for the field dependence of the spin gaps along all three principal axes, without resorting to additional interactions such as interchain coupling. A crossover to strong applied field behavior is predicted for further experimental verification.

Journal Article↗
PubMed2003

Coordination between donor cell type and cell cycle stage improves nuclear cloning efficiency in cattle.

Several studies have shown that both quiescent and proliferating somatic donor cells can be fully reprogrammed after nuclear transfer (NT) and result in viable offspring. So far, however, no comparative study has conclusively demonstrated the relative importance of donor cell cycle stage on nuclear cloning efficiency. Here, we compare two different types of bovine fetal fibroblasts (BFFs) that were synchronized in G(0), G(1), and different phases within G(1). We show that for non-transgenic (non-TG) fibroblasts, serum starvation into G(0) results in a significantly higher percentage of viable calves at term than synchronization in early G(1) or late G(1). For transgenic fibroblasts, however, cells selected in G(1) show significantly higher development to calves at term and higher post-natal survival to weaning than cells in G(0). This suggests that it may be necessary to coordinate donor cell type and cell cycle stage to maximize overall cloning efficiency.

Animals↗
PubMed2001

Studies on the hepatocyte protective activity and the structure-activity relationships of quinic acid and caffeic acid derivatives from the flower buds of Lonicera bournei.

13 quinic acid derivatives along with caffeic acid, methyl caffeate, myo-inositol, bis[5-formylfurfuryl] ether and 6,7-dihydroxycoumarin were isolated from the ethanol extract of the flower buds of Lonicera bournei Hemsl., among which 8 compounds were firstly obtained from this genus. The effects of different solvent soluble fractions of the ethanol extract and the pure compounds on heptocyte death induced by D-galactosamine (D-GalN)/tumor necrosis factor alpha (TNF-alpha) were studied, and the structure-activity relationships were also discussed.

Animals↗
PubMed2001

[Ectopic expression of human brain derived neurotrophic factor gene in fibroblasts].

The full-length sequence encoding hBDNF was inserted down into the enhancer-promotor regulatory element of Colia1 to construct minigene Colia1-BDNF. The recombinant eukaryotic expression plasmid pSCEPBFCAT was transfected into human fetal tendon fibroblasts in culture to realize ectopic expression of hBDNF gene in fibroblasts. The results of immuno-dot blot, Elisa and Western hybridization confirm that the expression protein with apparent molecular weight 27 kDa in pSCEPBFCAT transfected fibroblasts possesses antigen activity specific for the antibodies to BDNF.

Brain-Derived Neurotrophic Factor↗
PubMed2001

Ultrastructural study of mouse renal glomeruli under various hemodynamic conditions by an "in vivo cryotechnique".

Three-dimensional ultrastructure of mouse renal glomeruli under various hemodynamic conditions was studied by scanning electron microscopy with an "in vivo cryotechnique" followed by freeze-substitution. These results were also compared with those of conventionally fixed glomeruli at different perfusion pressures. Some kidneys of anesthetized mice were directly frozen in vivo under normal blood flow condition. Others were frozen in the same way after ligation of the lower abdominal aorta or their heart arrest. The frozen specimens were routinely freeze-substituted, freeze-dried and ion-sputtered for SEM. For another conventional fixation method, some kidneys were perfused with glutaraldehyde at pressures of 150 cm or 250 cm water, and other renal cortical tissues were routinely immersion-fixed with glutaraldehyde. In freeze-substituted specimens with the in vivo cryotechnique, interdigitating foot processes of podocytes exhibited smooth surface contours with less shrinkage and their surfaces were arranged more tightly than those seen by the conventional fixation method. In the anesthetized mice, filtration slits between the foot processes were found to be narrow after the heart arrest, but they were wide under the normal blood flow condition. After the aorta ligation, the filtration slits became wider and the foot processes were more elongated. The ultrastructure of capillary loops in functioning renal glomeruli were revealed to be dynamically changing in the living state, depending on various hemodynamic conditions.

Animals↗
PubMed2000

Probing superconducting phase fluctuations from the current noise spectrum of pseudogapped metal-superconductor tunnel junctions.

We study the current noise spectra of a tunnel junction of a metal with strong pairing phase fluctuation and a superconductor. It is shown that there is a characteristic peak in the noise spectrum at the intrinsic Josephson frequency omega(J) = 2eV when omega(J) is smaller than the pairing gap but larger than the pairing scattering rate. In the presence of an ac voltage, the tunneling current noise shows a series of characteristic peaks with increasing dc voltage. Experimental observation of these peaks will give direct evidence of the pair fluctuation in the normal state of high- T(c) superconductors and the pair decay rate can be estimated from the half width of the peaks.

Journal Article↗
PubMed2000

Thermodynamics of the bilinear-biquadratic spin-One heisenberg chain

The magnetic susceptibility and specific heat of the one-dimensional S = 1 bilinear-biquadratic Heisenberg model are calculated using the transfer matrix renormalization group. By comparing the results with the experimental data of LiVGe2O6 measured by Millet et al. [Phys. Rev. Lett. 83, 4176 (1999)], we find that the susceptibility data of this material, after subtracting the impurity contribution, can be quantitatively explained with this model. The biquadratic exchange interaction in this material is found to be ferromagnetic, i.e., with a positive coupling constant.

Journal Article↗
PubMed2000

Influence of a transmembrane protein on the permeability of small molecules across lipid membranes.

The influence of the nonchannel conformation of the transmembrane protein gramicidin A on the permeability coefficients of neutral and ionized alpha-X-p-methyl-hippuric acid analogues (XMHA) (X = H, OCH(3), CN, OH, COOH, and CONH(2)) across egg-lecithin membranes has been investigated in vesicle efflux experiments. Although 10 mol% gramicidin A increases lipid chain ordering, it enhances the transport of neutral XMHA analogues up to 8-fold, with more hydrophilic permeants exhibiting the greatest increase. Substituent contributions to the free energies of transfer of both neutral and anionic XMHA analogues from water into the bilayer barrier domain were calculated. Linear free-energy relationships were established between these values and those for solute partitioning from water into decadiene, chlorobutane, butyl ether, and octanol to assess barrier hydrophobicity. The barrier domain is similar for both neutral and ionized permeants and substantially more hydrophobic than octanol, thus establishing its location as being beyond the hydrated headgroup region and eliminating transient water pores as the transport pathway for these permeants, as the hydrated interface or water pores would be expected to be more hydrophilic than octanol. The addition of 10 mol% gramicidin A alters the barrier domain from a decadiene-like solvent to one possessing a greater hydrogen-bond accepting capacity. The permeability coefficients for ionized XMHAs increase with Na(+) or K(+) concentration, exhibiting saturability at high ion concentrations. This behavior can be quantitatively rationalized by Gouy-Chapman theory, though ion-pairing cannot be conclusively ruled out. The finding that transmembrane proteins alter barrier selectivity, favoring polar permeant transport, constitutes an important step toward understanding permeability in biomembranes.

Biological Transport↗
PubMed2000

Saponins from Lonicera bournei.

The lupane-triterpene glycosides, bourneioside A and bourneioside B, and two known saponins were isolated from Lonicera bournei Hemsl. The structures of bourneioside A and B were elucidated as 3-O-beta-D-glucopyranosyl-23-hydroxy-lup-20(29)-en-28-oic acid-28-O-beta-D-glucopyranosyl ester and 3-O-beta-D-glucopyranosyl-23-hydroxy-lup-20(29)-en-28-oic acid-28-O-[beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranosyl] ester, respectively, on the basis of spectral data and chemical evidence.

Glucosides↗
PubMed1998

The barrier domain for solute permeation varies with lipid bilayer phase structure.

The chemical selectivities of the transport barriers in lipid bilayers varying in composition and phase structure (gel-phase DPPC and DHPC bilayers and liquid-crystalline DPPC/CHOL/50:50 mol% bilayers) have been investigated by determining functional group contributions to transport of a series of alpha-substituted p-toluic acid analogs obtained in vesicle efflux experiments. Linear free energy relationships are established between the free energies of transfer for this series of compounds from water to the barrier domain and corresponding values for their transfer from water into six model bulk solvents (hexadecane, hexadecene, decadiene, chlorobutane, butyl ether, and octanol) determined in partitioning experiments to compare the barrier microenvironment to that in these model solvents. The barrier microenvironment in all bilayers studied is substantially more hydrophobic than octanol, thus establishing the location of the barrier beyond the hydrated headgroup interfacial region, as the interface is expected to be more hydrophilic than octanol. The chemical nature of the barrier domain microenvironment varies with bilayer phase structure. The barrier regions in non-interdigitated DPPC and interdigitated DHPC gel-phase bilayers exhibit some degree of hydrogen-bond acceptor capacity as may occur if these domains lie in the vicinity of the ester/ether linkages between the headgroups and the acyl chains. Intercalation of 50 mol% cholesterol into DPPC bilayers, which induces a phase transition to a liquid-crystalline phase, substantially increases the apparent barrier domain hydrophobicity relative to gel-phase bilayers to a nonhydrogen bonding, hydrocarbonlike environment resembling hexadecene. This result, combined with similar observations in liquid-crystalline egg-PC bilayers (J. Pharm. Sci. (1994), 83:1511-1518), supports the notion that the transition from the gel-phase to liquid-crystalline phase shifts the barrier domain further into the bilayer interior (i.e., deeper within the ordered chain region).

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1995

Interaction of wheat germ protein synthesis initiation factor eIF-(iso)4F and its subunits p28 and p86 with m7GTP and mRNA analogues.

The binding of p28, p86, and native wheat germ eIF-(iso)4F with m7GTP and oligonucleotides was measured and compared. The purified subunits (p28, 28 kDa and p86, 86 kDa) of wheat germ protein synthesis initiation factor eIF-(iso)4F have been obtained from Escherichia coli expression of the cloned DNA (van Heerden, A., and Browning, K. S. (1994) J. Biol. Chem. 269, 17454-17457). The binding of the 5'-terminal cap analogue m7GTP to the small subunit (p28) of eIF-(iso)4F as a function of pH, temperature, and ionic strength is described. The mode of binding of p28 to cap analogues is very similar to the intact protein. Assuming that all tryptophan residues contribute to p28 and eIF-(iso)4F fluorescence, iodide quenching shows that all 9 tryptophan residues in p28 are solvent-accessible, while only 6 out of 16 tryptophan residues are solvent-accessible on the intact eIF-(iso)4F. The fluorescence stopped-flow studies of eIF-(iso)4F and p28 with cap show a concentration-independent conformational change. The rate of this conformational change was approximately 10-fold faster for the isolated p28 compared with the native eIF-(iso)4F. From these studies it appears that cap recognition resides in the p28 subunit. However, p86 enhances the interaction with capped oligonucleotides and probably is involved in protein-protein interactions as well. Both subunits are required for helicase activity.

Base Sequence↗