Biomedical subjects

J Xu

Publications and source records attributed to J Xu.

At least 487 records · Page 27Linked to original sources

PubMed2000

[A Carnobacterium-like organism isolated form a patient with multiple bacterial synergistic gangrene].

An atypical lactic-acid producing gram positive rod Y6 strain was studied in this report, which was isolated form clinic sample of a patient with multiple bacterial synergistic gangrene, and could not be identified by routine method. A 1.5 kb of 16S rDNA of Y6 strain was synthesized and sequenced. Comparative 16S rDNA sequence analyses revealed that stain Y6 is most closely related to the genus of Carnobacterium. The overall similarity value between Y6 strain and Carnobacterium species are 93% to 97%. The signature nucleotides in 16S rDNA primary sequence of strain Y6 and that of genus of Carnobacterium were identical. The biological features of Y6 strain are very similar to that of Carnobacterium, such as lactic acid as main end product of in PYG broth, no gas produced form fermentation of glucose, catalase negative, no motility. Data suggested that Y6 strain is very similar to the genus of Carnobacterium, of which no strain has been isolated form clinical sample so far. Based on the results obtained, we names Y6 strain as Carnobacterium-like organism.

Base Sequence↗

PubMed2000

[Enzymatic synthesis of saccharide and saccharide alcohol fatty acid esters].

Conditions for esterification in tert-butanol using fatty acid as acy1 donor and saccharides or saccharide alcohols as acy1 acceptors, immobilized lipase from Candida sp. 1619 as biocatalyst were investigated. Optimal temperature and pH for esterication were 40 degrees C-45 degrees C and 5.5-7.5, respectively. Among the 13 acy1 donors compared, the best ones are the linoleic acid and oleic acid. The similar conversion degree was obtained when using saturated fatty acids with carbon chain length from C8 to C22. Among the 23 saccharides and saccharide alcohols compared, D-fructose, D-Xylose, trehalose, D-sorbitol, xylitol, mannitol isopropyidoneglucofruranose and alpha-methylglucopyranoside showed much higher esterification degree than other acy1 acceptors. In addition, the reaction degree of saccharide alcohols were substantially higher than that of the corresponding saccharides. The conversion was enhanced greatly when the molar ratio of acy1 donor to acy1 acceptor was higher than 2 to 1. In the case of using sorbitol and loeic acid as substrates, the reaction was carried out in 100 ml conical flask and the reaction system consisted of 3.0 mmol oleic acid(0.85 g), 0.2 mmol sorbitol(0.036 g), 3 mL tert-butanol, 30 mg immobilized lipase(600 u), shaken at 40 degrees C. After reaction for 48 h, more than 90% of sorbitol was esterified based on equal molar of substrates. The products were identified TLC as monoester and diester.

Candida↗

PubMed2000

[Selection and recombinant expression of an immunodominant B cell epitope of HIV gp41].

A novel method was designed for disease-specific B cell epitope mapping and epitope expression in E. coli. A phage library displaying random dodecamers was biopanned first with human total IgG antibodies against HIV-1, and then non-specific phages were subtracted by HIV(-) polyclonal antibodies. After three rounds of screening, the positive phages were tested in an ELISA for their reactivity with HIV(+)-IgG and HIV(-)-IgG antibodies. Phages that showed positive reactivity with HIV(+)-IgG, but negative to HIV(-)-IgG, were selected and their displayed peptides were determined by DNA sequencing. All the 13 positive clones sequenced displayed five kinds of peptides (SPKCLGKLLCAF, THQCLGKLQCGV, SCSAKFTCTTQI, KSDCSARFMCSV, DCLKQWACEWSR) that have homology to the HIV-1 gp41(602GCSGKLICTTNV613), demonstrating there is a dominant epitope in the region.

Enzyme-Linked Immunosorbent Assay↗

PubMed2000

[Amplification, cloning and expression of a gene encoding hexose transporter of Plasmodium falciparum].

OBJECTIVE: To amplify, clone and express of a gene encoding hexose transporter of Plasmodium falcipuram (PfHT1) from Southern China isolate FCC1/HN for studing the immune of recombinant which protective from malaria parasite infection. METHODS: Cultivation of P. falciparum isolate FCC1/HN in vitro; extraction of genomic DNA from FCC1/HN using the alkali specific cleavage method; PCR amplification of PfHT1 and cloning into eukaryotic expression vector, pEGFPN3. The recombinant as introduced into mammalian cells, HEPG2 by using liposome-mediated transfection. RESULTS: The gene encoding PfHT1 was specifically amplified from the genomic DNA of P. falciparum isolate FCC1/HN. The size of amplified fragment was 1,516 base pair. The eukaryotic expression recombinant, pN3-HT1, was constructed and expressed steadily in the hepatocarcinoma cell lines, HEPG2. CONCLUSION: The gene encoding PfHT1 was successfully amplified and cloned. The pN3-HT1/HEPG2 cell line was built for expressing fusion protein of GFP-HT1.

Animals↗

PubMed2000

[Infiltration of dendritic cells into cervical lymph nodes in laryngeal carcinoma].

OBJECTIVE: Dendritic cells(DC) form a system of highly efficient antigen-presenting cells. An immunohistochemical study was performed to prove their role in immune responses against cancer. METHODS: Paraffin blocks were prepared for staining with antibody against S-100 proteins in 157 lymph nodes obtained from elective cervical lymphadenectomy in 47 cases of laryngeal squamous cell carcinomas. RESULTS: The extent of infiltration by DC into the regional lymph nodes was evaluated in two groups according to negative and positive lymph node metastasis. Densities of DC ranged from 23.0 to 111.9, with an average of 57.2 +/- 16.0, in the negative metastasis nodes; and from 17.5 to 63.6, with an average of 38.3 +/- 14.9, in the positive metastasis nodes. The test revealed that the differences in population density between the two groups were significant (P < 0.001). Quantitative analysis showed that patients who survived longer than 5 years had significant higher numbers of DC in the lymph nodes than those who lived less than 5 years (P < 0.001). Densities of DC ranged from 32.0 to 111.9, with an average of 61.6 +/- 19.6, in the nodes of 20 cases of patients who survived longer than 5 years and from 17.5 to 65.8, with an average of 37.9 +/- 13.7, in the nodes of 27 cases of patients who survived less than 5 years. CONCLUSION: DC may be more directly involved in the host immune reaction against tumor by means of the most important antigen-presenting cells. DC in the cervical lymph nodes are important for establishing immunologic defense mechanisms in cases of laryngeal carcinomas, and the densities of DC can serve as a useful indicator in assessing prognosis of laryngeal carcinomas.

Adult↗

PubMed2000

[Synthesis and spectroscopic characterization of a new blue light-emitting material complexes and study of its photoluminescence and electroluminescence characterization].

The Zn-complexe emitting blue light was synthesised and characterized spectroscopically by elemental analysis, UV, EX, EM, IR. Photoluminescence and electroluminescence characterization of the light-emitting diodes using Zn-complexe as the emissive layer was studied, it could emit blue light with a peak wavelength at 455 nm and a brightness of about 37.2 cd.m-2.

Chelating Agents↗

PubMed2000

[Determination of artificial synthetic pigment by excitation spectrophotometry].

Solid phase spectrophotometry is a mew, simple, fast and sensitive trace analytical method. In this report, it is presented with a method that the polyamide was used for the absorbance and the excitation spectra was measured directly. The background of the solid phase spectrophotometry was overcome, the sensitivity was increased in a big way. The method is good standard addition recovery and precision, high accuracy. Not only the trace inorganic ion can be analysed by the solid phase method, but also the artificial synthetic pigment, the result was satisfied.

Adsorption↗

PubMed2000

[Orientation of H-bonds revealed by cryogenic FTIR spectroscopy].

We propose a new way to reveal structural arrangement of hydrogen bond network using FTIR spectroscopy. When KBr pellet and fluorolube mull methods are used to prepare samples for IR measurements, the resultant spectra sometimes show significant differences, sometimes not. The reason is unknown. We use cryogenic FTIR spectra to prove pressure effect accounts for spectral variation in different sampling process. The sensitivity of the FTIR spectra to external pressure is related to the three-dimensional arrangement of hydrogen bonding network in the sample. When hydrogen bonds are in one plane, they can not resist external pressure applied perpendicular to that plane. Consequently, large differences appear between the spectra obtained using KBr pellet and fluorolube mull methods. On the other hand, when hydrogen bonds orientate towards various directions, the hydrogen bonding system can resist pressure from any directions. Thus, the FTIR spectra exhibit little variation using different sampling methods. We propose that the spectral variation obtained using above methods is a criterion to judge whether the hyrogen bonds orientate toward various directions in three-dimensional space or not.

Cholesterol↗

PubMed2000

[Photoluminescence characteristics of mixed aggregates in Langmuir-Blodgett multilayers].

Effects of the mixed aggregates of different active molecules and UV illumination on photoluminescence(PL) spectra of Langmuir-Blodgett multilayers were investigated. The strong interaction between hemicyanine and stilbazolium salt molecules in the mixed films caused a blue or red shift of the fluorescence band with respect to that of interleaving hemicyanine or stilbazolium salt/arachidic acid multilayers. UV illumination would dissociate the aggregates even more destroy the molecular structure, leading to a significant reduction of fluorescence intensity.

English Abstract↗

PubMed1999

Evolution of shape complementarity and catalytic efficiency from a primordial antibody template.

The crystal structure of an efficient Diels-Alder antibody catalyst at 1.9 angstrom resolution reveals almost perfect shape complementarity with its transition state analog. Comparison with highly related progesterone and Diels-Alderase antibodies that arose from the same primordial germ line template shows the relatively subtle mutational steps that were able to evolve both structural complementarity and catalytic efficiency.

Antibodies, Catalytic↗

PubMed1999

Linkage studies of D2 and D4 receptor genes and alcoholism.

The purpose of the present study was to evaluate two polymorphisms near the D2 receptor gene (TaqI A RFLP and C microsatellite) and a VNTR for D4. A nonparametric linkage (NPL) technique, SIBPAL, was used to test for the presence or absence of linkage in 54 multiplex alcoholic families. These families had been ascertained through two alcoholic proband siblings in order to increase the density of alcoholic cases within these pedigrees. Phenotypic definitions of alcoholism were manipulated in an effort to determine the impact of severity (signs of physical dependence, early age of onset, presence of antisocial personality disorder) on the likelihood of finding positive evidence for linkage. A regression analysis that simultaneously evaluated the allele sharing identical by descent for Feighner criteria alcoholism in affected, unaffected, and discordant sib pairs (SIBPAL) for two D2 polymorphisms and the D4 polymorphism gave no evidence for linkage. Phenotypes associated with greater alcoholism severity (presence of physical dependence symptoms, earlier onset, or comorbid antisocial personality disorder) revealed some evidence for linkage. The presence of one or more physical dependence symptoms in combination with Feighner criteria alcoholism provided some evidence favoring linkage (TaqI A and D4). Alcoholics with an earlier onset of alcoholism showed some evidence for linkage especially when the presence of physical dependence was required (e. g., morning drinking, wanted to stop drinking but could not, binges or benders, and evidence of withdrawal symptoms). Finally, alcoholics with antisocial personality disorder differed significantly in their allele sharing from nonalcoholics for both D2 polymorphisms. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:676-685, 1999.

Adolescent↗

PubMed1999

The mass spectral fragmentation of 1a,3-disubstituted 4-benzoyl-1a,2,3,4- tetrahydrooxazirino

The mass spectrometric behaviour of four 1a,3-disubstituted 4-benzoyl-1a,2,3,4-tetrahydrooxazirino[2,3-a][1,5]benzodiazepines has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization. All compounds show a tendency to eliminate a neutral oxygen atom, or oxygen atom plus benzoyl or aryl radicals, or oxygen atom plus CO molecule to yield 2,3-dihydro-1H-1,5-benzodiazepine derivative ions, or 1-benzoyl-2,3-dihydro-1H-1,5-benzodiazepine ions, which could further lose benzoyl to give 2,3-dihydro-1H-1,5-benzodiazepine ions. All compounds also show a tendency to eliminate a benzoyl radical to produce 1a,2,3,4-tetrahydrooxazirino[2,3-a][1,5]benzodiazepine ions. Both oxazirino[2,3-a][1,5]benzodiazepine ions and 2,3-dihydro-1H-1,5-benzodiazepine ions can undergo diazepine ring contraction rearrangement to yield benzimidazole ions by loss of propene or styrenes and other small fragments. The oxazirino[2,3-a][1,5]benzodiazepine ions [M(+)-PhCO] also undergo rearrangement reactions to form benzoxazole ions and benzimidazole ions. Copyright 1999 John Wiley & Sons, Ltd.

Journal Article↗

PubMed1999

Pharmacokinetic factors and concentration-time threshold in m-dinitrobenzene-induced neurotoxicity.

m-Dinitrobenzene is a multitarget toxicant. This study presents a concentration-time threshold model in m-dinitrobenzene (m-DNB)-induced neurotoxicity in F344 rats based on pharmacokinetic modeling and variable duration infusions with neuropathological end points. Pharmacokinetic parameters for m-DNB were determined after giving a single i.v. dose of 10 mg/kg m-DNB. Time dependency of the brain lesions was studied by either giving a single bolus i.v. dose of 30 mg/kg m-DNB or infusing this dose over 6, 12, or 24 h, or 2, 4, 6, 8, or 14 days. The results show that the 6-day infusion, in which the theoretical steady-state blood concentration was 2.0 microM, caused brain damage, whereas the 8- and 14-day infusions, in which the steady-state blood concentrations were 1.5 and 0.8 microM, respectively, did not induce apparent brain damage. When this dose was infused over 6 h, the peak blood concentration of m-DNB was 35 microM and the time (T(m)) for which m-DNB exceeded the 2-microM concentration threshold was 18.8 h, but no brain damage was observed. However, when the same total dosage was infused over periods of either 12 or 24 h, or 2, 4, or 6 days, the theoretical blood concentrations were from 21.9 to 2.0 microM and the T(m) was from 22. 7 to 144 h, and brain damage was produced. Hence a T(m) of 22.7 h was considered to be the time threshold for m-DNB-induced brain damage. It is concluded that a high concentration alone does not result in m-DNB-induced neurotoxicity and that in addition to a concentration threshold, there also exists a time threshold. Both apparently need to be exceeded before neurotoxicity is seen.

Aniline Compounds↗

PubMed1999

The cAMP receptor protein CRP can function as an osmoregulator of transcription in Escherichia coli.

Transcription of the P1 promoter of the Escherichia coli proP gene, which encodes a transporter of osmoprotectants, is strongly induced by a shift to hyperosmotic media. Unlike most other osmotically regulated promoters, the induction occurs for a brief period of time, corresponding to the replacement of intracellular K(+) glutamate with osmoprotecting compounds. This burst of proP transcription is correlated with the osmolarity-dependent binding of the cAMP receptor protein CRP to a site within the proP P1 promoter. We show that CRP-cAMP functions as an osmotically sensitive repressor of proP P1 transcription in vitro. Binding of CRP to the proP promoter in vivo is transiently destabilized after a hyperosmotic shift with kinetics that correspond to the derepression of transcription, whereas Fis and Lac repressor binding is not osmotically sensitive. Similar osmotic regulation of proP P1 transcription by the CRP* mutant implies that binding of cAMP is not responsible for the unusual osmotic sensitivity of CRP activity. Osmotic regulation of CRP activity is not limited to proP. Activation of the lac promoter by CRP is also transiently inhibited after an osmotic upshift, as is the binding of CRP to the galdelta4P1 promoter. These findings suggest that CRP functions in certain contexts to regulate gene expression in response to osmotic changes, in addition to its role in catabolite control.

Bacterial Proteins↗

PubMed1999

Circulating CD2+ monocytes are dendritic cells.

Low levels of CD2 have been described on subsets of monocytes, macrophages, and dendritic cells. CD2 is expressed on about one-third of circulating monocytes, at levels one-half log lower than on T or NK cells, representing 2-4% of PBMC. FACS analysis of CD2+ and CD2- monocytes revealed no significant difference in the expression of adhesion molecules (CD11a/b/c), class II Ags (HLA-DR, -DQ, -DP), myeloid Ags (CD13, CD14, CD33), or costimulatory molecules (CD80, CD86). Freshly isolated CD2+ and CD2- monocytes were morphologically indistinguishable by phase contrast microscopy. However, scanning electron microscopy revealed large prominent ruffles on CD2+ monocytes in contrast to small knob-like projections on CD2- monocytes. After 2 days of culture, the CD2+ monocytes largely lost CD14 expression and developed distinct dendrites, whereas the CD2- monocytes retained surface CD14 and remained round or oval. Freshly isolated CD2+ monocytes were more potent inducers of the allogeneic MLR and more efficiently induced proliferation of naive T cells in the presence of HIV-1 gp120 than did CD2- monocytes. After culture in the presence of GM/CSF and IL-4, CD2+ monocytes were up to 40-fold more potent than monocyte-derived dendritic cells or CD2- monocytes at inducing allogeneic T cell proliferation. These findings suggest that circulating CD2+ and CD2- monocytes are dendritic cells and the precursors of macrophages, respectively. Thus, dendritic cells are far more abundant in the blood than previously thought, and they and precursors of macrophages exist in the circulation as phenotypically, morphologically, and functionally distinct monocyte populations.

Antigen Presentation↗

PubMed1999

Localization of amino acids required for Fis to function as a class II transcriptional activator at the RpoS-dependent proP P2 promoter.

ProP is an integral membrane transporter of proline, glycine betaine, and several other osmoprotecting compounds. Fis plus RpoS collaborate to promote a burst of proP transcription in late exponential growth phase. This brief period of ProP synthesis enables stationary phase cells to cope with a potential hyperosmotic shock. Fis activates the RpoS (sigma(38))-dependent proP P2 promoter by binding to a site within the promoter region centered at -41 and thus functions as a class II activator. We show here that activation by Fis at this promoter is completely dependent upon the alpha-CTD of RNA polymerase and that the activation domain on Fis is localized to a four amino acid ridge on the surface of Fis adjacent to the helix-turn-helix DNA binding domain in only one subunit of the homodimer. Fis mutants containing amino acid substitutions within this region are defective in cooperative binding interactions with the sigma(38)-form of RNA polymerase. Some of these substitutions also alter interactions with DNA sequences flanking the core binding site, but we show that changes in Fis-mediated curvature do not affect promoter activity. We conclude that the same amino acids are used by Fis to activate transcription from a class I (-71, rrnB P1) and class II (-41, proP P2) location, but this region is distinct from that required to regulate the Hin site-specific DNA inversion reaction.

Arginine↗

PubMed1999

Modulation of enediyne-induced DNA damage by chromatin structures in transcriptionally active genes.

To better understand how the cellular environment of DNA affects it as a target for genotoxins, we have used ligation-mediated PCR to map DNA damage produced by two DNA-cleaving enediyne antibiotics, esperamicins A1 and C, in the transcriptionally active human p53 and phosphoglycerate kinase (pgk1) genes in vivo. Esperamicin A1, which is limited to damaging the linker region between nucleosome cores due to intercalation of an anthranilate moiety, did not detect the presence of a nucleosome proposed to reside between exons 5 and 6 of p53. This may be due to the absence of a nucleosome at this site in the p53 gene or to the altered structure of nucleosomes in transcriptionally active genes. In studies of the upstream region of the active pgk1 gene, we found that DNA damage produced by both enediynes was enhanced in sequences located between several transcription factor binding sites, while patterns of DNA damage within the binding sites were consistent with known drug binding modes and structures of the protein-DNA complexes. For both drugs, the DNA sequence appeared to be the major determinant of the location of DNA damage, with chromatin structures modulating the quantity of DNA damage.

Aminoglycosides↗

PubMed1999

The Gelation of CO(2): A Sustainable Route to the Creation of Microcellular Materials.

Compounds with strong thermodynamic affinity for carbon dioxide (CO(2)) have been designed and synthesized that dissolve in CO(2), then associate to form gels. Upon removal of the CO(2), these gels produced free-standing foams with cells with an average diameter smaller than 1 micrometer and a bulk density reduction of 97 percent relative to the parent material.

Journal Article↗