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Biomedical subjects

G Q Xu

Publications and source records attributed to G Q Xu.

15 recordsLinked to original sources
PubMed2001

Selective binding of the cyano group in acrylonitrile adsorption on Si(100)-2 x 1.

The covalent binding of acrylonitrile (CH(2)=CH-C triple bond N) and the formation of a C=C-C=N structure on Si(100) have been investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and density functional theory (DFT) calculations. For chemisorbed acrylonitrile, the absence of nu(C triple bond N) at 2245 cm(-1) and the appearance of nu(C=N) at 1669 cm(-1) demonstrate that the cyano group directly participates in the interaction with Si(100), which is further supported by XPS and UPS observations. Our experimental results and DFT calculations unambiguously demonstrate a [2 + 2] cycloaddition mechanism for acrylonitrile chemisorption on Si(100) through the binding of C triple bond N to Si dimers. The resulting chemisorbed monolayer with a C=C-C=N skeleton can serve as a precursor for further chemical syntheses of multilayer organic thin films in a vacuum and surface functionalization for in situ device fabrication.

Journal Article↗
PubMed2001

A study of titanium nitride diffusion barriers between aluminum and silicon by X-ray absorption spectroscopy: the Si, Ti and N results.

We report a multi-elment, multi-edge and multi-detection mode X-ray photoabsorption study of a series of Al/TiN(x)/Si(100) thin films as a function of the TiN(x) film thickness (100A-500A) and of the annealing temperature (400 degrees C-600 degrees C). The Si K- and L-edge results show that Si does not diffuse to the surface for all the films. The high resolution Ti L-edge and N K-edge spectra show that the TiN(x) layer undergoes a dramatic chemical reaction with the gradual increase in the annealing temperature. This chemical reaction stabilizes at 560 degrees C at which the TiN(x) film is known to fail to act as an effective diffusion barrier between Al and Si.

Journal Article↗
PubMed2001

Preparative isolation and purification of lutein from the microalga chlorella vulgaris by high-speed counter-current chromatography.

High-speed counter-current chromatography (HSCCC) was applied to the isolation and purification of lutein from microalgae. Analytical HSCCC was used for the preliminary selection of a suitable solvent system composed of n-hexane-ethanol-water (4:3:1, v/v). Using the above solvent system, preparative HSCCC was successfully performed yielding lutein at 98% purity from 200 mg of the crude extract in a one-step separation.

Chlorella↗
PubMed1996

[Analysis of the clinic with pathology and detection using IGSS of 201 cases of discoid lupus erythematosus]

Clinic pathology and detection using IGSS of 201 cases of discoid lupus erythematosus (DLE) were studied in this paper.The results showed:1.DLE usually occured on the low lip(60%);2.Suffering from gastrointestinal disease were the first symptom(25%DLE cases was confirmed by mild dysplasia,3 cases of carcinoma.1 cases Combined of DLE and lichen planus(LP);4.Immunogold-silver Staining (IGSS) was applied to detect immune complex.The result indicated that Fg,immunoglobins and complement C3 deposited at basal membrane zone of DLE.It is illustrated that DLE is an autoimmune disease which is caused by many kinds of factors and may be cancerous.Coexistence of DLE and LP suggested that they may be at different stages of the same disease.Its mechanism will be further studied.

Journal Article↗
PubMed1994

Copper distribution in fetus and placenta of the macular mutant mouse as a model of Menkes kinky hair disease.

Menkes kinky hair disease (MKHD) in humans is caused by a disturbance in copper homeostasis. A mutant mouse shows clinical and biochemical features very close to MKHD. In an attempt to elucidate the defect in copper transport, the copper distribution in various organs of 18-gestational-day-old macular mouse embryos, following administration by a single injection of saline (control) or 50 micrograms of CuCl2 on day 16 of gestation or by two injections on days 15 and 17 of gestation to the dams, was examined both biochemically and histochemically. The copper content in the hemizygous fetus (Ml/y) born to the homozygous mother, who had no copper injection during gestation, was lower in the brain and liver but higher in the placenta than in the respective organs of the normal fetus. When 50 micrograms of CuCl2 was injected into heterozygous dams (Ml/+) on day 16 of gestation, their hemizygous fetuses showed a slight increase in the copper content in the brain and liver, but the amount of copper in these organs was still less than that of the normal fetus. Conversely, the copper content in the placenta of the hemizygous fetus was far higher than that of the normal fetus. In the copper staining of the fetuses harvested from heterozygous dams, some fetuses showed copper deposition in the placenta, but not in the liver. The others showed no copper deposit in both the placenta and liver, thus indicating that the former were hemizygous for the mutation and the latter were normal littermates.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Analysis of the regulatory and structural defects of troponin C central helix mutants.

Five deletion mutants of the D/E linker region of the troponin C central helix were tested for conformational and functional differences from wild-type troponin C. The mutants were in the region 87KEDAKGKSEEE97: dEDA, dKG, dKGK, dKEDAKGK, and dSEEE, designed to change the length of the central helix and the orientation of the Ca(2+)-binding domains relative to each other [Dobrowolski, Z., Xu, G.-Q., & Hitchcock-DeGregori, S.E. (1991) J. Biol. Chem. 266, 5703-5710]. Previous work showed that all mutants except dSEEE are partially defective in one part of the Ca2+ switch or the other. All mutants undergo Ca(2+)-dependent conformational changes as detected by changes in electrophoretic mobility, alpha-helix content, and hydrophobic exposure. Deletions of the central helix do not extensively alter the thermal stability of troponin C, as determined by temperature-dependent loss of alpha-helix. There are differences among the mutants that do not correlate with function. All troponin C mutants show Ca(2+)-dependent interaction with troponin I and T in polyacrylamide gels. Troponin I-troponin C interaction was also analyzed by Ca(2+)-dependent increase in the monomer/excimer ratio of tropinin I and relief of inhibition of the actomyosin S1 ATPase. While all mutants retain basic function, dKGK, dKEDAKGK, and dEDA have altered interaction with troponin I in the absence of Ca2+. dSEEE differs in conformation from wild type, but it is normal in functional assays. This conserved region of the D/E linker is not required for interaction with troponin I in the presence or absence of urea.

Amino Acid Sequence↗
PubMed1991

Modified calcium-dependent regulatory function of troponin C central helix mutants.

Mutations have been made in the exposed region of the avian troponin C central helix, the D/E linker, which change its length and the orientation of the Ca2(+)-binding domains relative to each other. The region 87Glu-Asp-Ala-Lys-Gly-Lys-Ser-Glu-Glu-Glu97 has been altered in five deletion (d) mutants: dEDA, dKG, dKGK, dSEEE, and dKEDAKGK. The recombinant troponin Cs were expressed in Escherichia coli, purified, and assayed for function. All mutants retained basic troponin C function. They all bound Ca2+ to the low and high affinity sites, and they all were able to confer Ca2+ sensitivity on the regulated actomyosin ATPase. However, the regulatory function of all mutants except dSEEE was defective in one part of the Ca2+ switch or the other. In certain conditions dKGK and dKEDAKGK failed to inhibit fully whereas dEDA and dKG failed to activate the regulated actomyosin ATPase fully. The following general conclusions have been made. (a) The length of the D/E linker per se (assuming the linker is helical) and the orientation of the two Ca2(+)-binding domains relative to each other are not crucial for regulation. (b) The conserved charge cluster 95Glu-Glu-Glu97, in a region of troponin C known to bind to troponin I and postulated to be required for regulation, appears to be unimportant for function. (c) Deletion of 88Glu-Asp-Ala90 resulted in a troponin C that could not activate the actomyosin (or S1) ATPase over the level of actomyosin alone, thus defining a role for troponin C in this aspect of thin filament regulation. The results have been interpreted in terms of the crystallographic structure of troponin C and related to results with analogous calmodulin mutants.

Amino Acid Sequence↗
PubMed1991

[Effect of enhancers on cutaneous permeation of piroxicam in vitro].

Enhancing effects on the permeation of piroxicam (Pir) through excised hairless mouse (inbred HRS mice) skin were investigated by measuring flux. Azone 1% was found to be the most effective enhancer studied, increasing the flux about 21 times. The effect of Azone was enhanced by the presence of propylene glycol. Oleic acid, ethylacetate, and ethanol promoted the diffusion of Pir. Other enhancers, such as DMSO, PEG 400, acetone, urea and salicylic acid, showed little or no effect. Pir-beta-cyclodextrin inclusion compound increased the flux about 3 times. The results revealed that lipophilic enhancers were more effective than lipophobic ones.

Animals↗
PubMed1990

[Study on prolonged action cefotoxime].

A prolonged action cephalosporin was prepared by the reaction of cefotaxime sodium (CTX) with N,N-dibenzylethylene diamine acetate. It is reasonable to consider the resultant as benzathine cefotaxime (BCTX) by means of elemental analysis, DSC, UV spectra, IR spectra, NMR spectra and mass spectra. In contrast to CTX, BCTX appeared to be almost insoluble in water and its intrinsic dissolution rate was 0.183 micrograms/ml.min. The stability revealed that the degradation of BCTX suspension in water followed zero-order kinetics and the rate of degradation at room temperature was found to be 1.67 X 10(-7) mg/ml.s. An in vivo test by using 12 rabbits given BCTX suspension and CTX solution intramuscularly was conducted. The results showed that the former was longer in maintaining serum drug level than the latter.

Animals↗
PubMed1988

Synthesis of a troponin C cDNA and expression of wild-type and mutant proteins in Escherichia coli.

An avian fast striated muscle troponin C cDNA was designed and synthesized from six oligonucleotides using the overlap-fill in method and overproduced in Escherichia coli for the purpose of developing recombinant DNA approaches to study structure-function relationships in this calcium-binding regulatory protein. The recombinant protein isolated from E. coli functions as a bona fide troponin C in all properties that were assayed: calcium binding, calcium-dependent conformational change, calcium-dependent interaction with troponin I, and formation of a functional ternary complex with troponin I and troponin T that can confer calcium sensitivity on the actomyosin MgATPase. The initiating methionine was removed by E. coli leaving alanine as the first amino acid, as in the muscle troponin C. The first amino acid was not acetylated, but this difference from the muscle protein has no apparent effect on the function. The presence of Glu at position 99, as in turkey, versus Ala in chicken resulted in no detectable difference in comparing recombinant with chicken troponin C. A mutant in which residues 91-93 (Lys-Gly-Lys) in the D/E helical linker were deleted differs in function from wild-type troponin C in the conformational change that takes place upon calcium binding and its interaction with troponin I. Also, the mutant troponin C is impaired in its ability to form a functional complex with troponin I and troponin T that will confer calcium sensitivity on the actomyosin MgATPase.

Actomyosin↗
PubMed1984

The cooperative behavior of yeast D-glyceraldehyde-3-phosphate. Dehydrogenase as studied by the formation of the fluorescent NAD derivative.

The ultraviolet irradiation of the yeast D-glyceraldehyde-3-phosphate dehydrogenase carboxymethylated at the active site Cys residues, as with the rabbit muscle enzyme, led to the formation of a fluorescent NAD derivative with an emission maximum at 410 nm. Similar results were obtained with the enzyme selectively carboxymethylated at only 2 of its 4 active site Cys residues. The binding of NAD+ to both the carboxymethylated enzymes is non-cooperative or only weakly negatively cooperative when determined by NAD+ quenching of the intrinsic protein fluorescence. However, determinations of the amount of fluorescent NAD derivative formed under different NAD+ concentrations show that both the carboxymethylated enzymes appeared to bind NAD+ with positive cooperativity as in the case of the binding of NAD+ to the native apoenzyme. This seems to suggest that the spatial positioning of the nicotinamide moiety at the active site of the irradiated enzyme resembles more closely that of the nicotinamide ring in the native holoenzyme as compared to the carboxymethylated enzymes.

Allosteric Regulation↗