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Biomedical subjects

X Cheng

Publications and source records attributed to X Cheng.

287 records · Page 16Linked to original sources
PubMed1990

Base changes at position 792 of Escherichia coli 16S rRNA affect assembly of 70S ribosomes.

To investigate the function of base 792 of 16S rRNA in 30S ribosomes of Escherichia coli, the wild-type (adenine) residue was changed to guanine, cytosine, or uracil by oligonucleotide-directed mutagenesis. Each base change conferred a unique phenotype on the cells. Cells containing plasmid pKK3535 with G792 or T792 showed no difference in generation time in LB broth containing ampicillin, whereas cells with C792 exhibited a 20% increase in generation time in this medium. To study the effect on cell growth of a homogeneous population of mutant ribosomes, the mutations were cloned into the 16S rRNA gene on pKK3535 carrying a spectinomycin-resistance marker (thymine at position 1192), and the cells were grown with spectinomycin. Cells containing G792 or C792 showed 16% and 56% increases in generation time, respectively, and a concomitant decrease in 35S assimilation into proteins. Cells with T792 did not grow in spectinomycin-containing medium. Maxicell analyses indicated decreasing ability to form 70S ribosomes from 30S subunits containing guanine, cytosine, or uracil at position 792 in 16S rRNA. It appeared that C792-containing 30S ribosomes had lost the ability to bind initiation factor 3.

Base Sequence↗
PubMed1990

[Chemical constituents of Agapetes obouata S. H. Huong].

Six compounds were isolated from Agapetes obouata. On the basis of physico-chemical constants and spectral analysis they were identified as friedelin (I), fernenal (II), beta-sitosterol (III), daucosterol (IV), beta-sitosterol glucutonide (V) and n-tridecane (VI) respectively.

Drugs, Chinese Herbal↗
PubMed1990

[Purification and characterization of beta-N-acetyl hexosaminidase from Aspergillus tamarii].

A beta-N-acetylhexosaminidase from mycelium-free culture filtrate of Asp tamarii S215 was purified to PAGE homogenous by ammonium sulfate and polyethylene glycol fractionation precipitation followed by Sephadex G-50 desalt, DEAE-Sephadex A-25 chromatography, hydroxyapatite chromatography and DEAE-Sephadex A-25 rechromatography with 170-fold purification and 24.7% recovery. The ratio of the beta-GlcNAcase and beta-GalNAcase was 2.5 and remained constant throughout the purification. The Mr estimated with concentration gradient PAGE was 140,000 and subunit Mr determined with SDS-PAGE was 72,000, the number of subunit were 2. The pI was 4.2 determined by PAGIEF. The optimum pH was 5.5-6.5 and 5.0-6.0 for beta-GlcNAcase and beta-GalNAcase respectively with stable pH range 5.5-8.3 for both. The optimum temperature was 60 degrees C for beta-GlcNAcase and beta-GalNAcase. The residual activity of beta-GlcNAcase was 52.7% after treated at 50 degrees C for 8 h and it was 44.9% for beta-GalNAcase. The residual activities of both were down to 1% after treated at 62 degrees C for 10 min. The activity was slightly activated by Mn2+ or Fe2+, while strongly inhibited by Hg2+ and slightly by Ag+, Cu2+, Pb2+, Cd2+ or Zn2+. Analyses of amino acids composition showed that the beta-HexNAcase contained about 24.2% acidic amino acids and 14.9% basic amino acids and only 0.6% methionine.

Acetylglucosaminidase↗
PubMed1990

[Epidemiologic survey of migraine in six cities of China].

A door-to-door survey was carried out in six cities of China. A total of 63,195 individuals were sampled during 1983 to determine the prevalence of major neurological disorders including migraine. The survey involved a complete census, together with a pretested interview and brief screening examination with a high level of sensitivity for detecting individuals with migraine. All those with responses suggestive of severe headaches were requested to be examined by a senior neurologist using defined clinical criteria to establish the final diagnosis. Based on 396 prevalent cases of migraine, the crude and age-adjusted (to the 1960) total population of the United States point prevalence rate were 6.3 per 1000, and 5.4 per 1000 respectively. The prevalence among the females was nearly 3.5 times the figure for the males. For individuals above the age of 40, the age-specific prevalence rate declined with increasing age. The survey was followed by a case-control pairs matched by age, sex and geographic regions. A family history with "similar headache" seemed to be a significant risk factor while smoking and alcohol consumption appeared to be other relevant factors associated with the occurrence of migraine were also investigated. It seemed to the authors that the most frequently associated factors were psychological and hormonal factors.

Adult↗
PubMedDate not supplied

Interactions between single-stranded DNA binding protein and oligonucleotide analogs with different backbone chemistries.

Chemical modification of backbone structures has been an important strategy in designing oligonucleotides capable of improved antisense effects. However, altered backbone chemistry may also affect the binding of oligonucleotides to key cellular proteins, and thus may impact on the overall biological action of antisense agents. In this study we have examined the binding of oligonucleotides having four different backbone chemistries to single-strand binding protein (SSB), a protein having a key role in DNA repair and replication. The oligomers tested had the same sequence, while the internucleoside linkages were phosphodiester (PO), phosphorothioate (PS), phosphorodithioate (PS2), or methylphosphonate (MP). We found that both PS and PS2 oligomers bound to SSB with higher affinity than PO oligonucleotides, while MP oligonucleotides did not bind appreciably at the concentrations tested. Oligonucleotide length was also an important factor in binding to SSB, but sequence was less critical. These observations indicate that backbone chemistry is an important factor in interactions between oligonucleotides and critical cellular proteins, and thus may be a key determinant of the biological effects of antisense oligonucleotides.

Binding, Competitive↗
PubMedDate not supplied

The effect of orientation within a chimeric peptide on the immunogenicity of Chlamydia trachomatis epitopes.

Peptides representing the Chlamydia trachomatis major outer membrane protein variable domains (VD) 1 and 4 of serovars C and E, respectively, have been shown to elicit a neutralizing antibody response in mice. To assess whether the position within a chimeric peptide influences the immunogenicity of the epitopes, two constructs, VD 1-4 and VD 4-1, were made in which the position of the VD relative to the amino and carboxy terminals were rotated. C57BL/10 mice were immunized with 100 micrograms of peptide in complete Freund's adjuvant (FA) on day 0, followed by an immunization with peptide (100 micrograms) in complete FA on day 14. By day 21 the immunodominant epitope in both chimeras as measured by ELISA was the one located at the carboxy terminus. A pepscan of the VD 1-4 antisera revealed a main peak in VD 4 which had been previously identified by neutralizing MAbs. The VD 4-1 antisera gave a peak in the VD 1 region which did not correspond to regions previously mapped with neutralizing MAbs. The VD 1-4 antisera but not the VD 4-1 antisera was able to neutralize in vitro serovar E. In summary, the position of these chlamydial epitopes within a chimeric peptide greatly influenced the resulting immune response.

Amino Acid Sequence↗
PubMedDate not supplied

Catalytic subunit of cyclic AMP-dependent protein kinase: structure and dynamics of the active site cleft.

The catalytic subunit of cyclic AMP-dependent protein kinase serves as a structural template for the entire family of Ser, Thr, and Tyr specific protein kinases. We review here the dynamics of the active catalytic subunit. These dynamics correlate with an opening and closing of the active site cleft, and are considered to be a requirement for catalysis. The motions, described by a set of several crystal structures, reveal a very fluid active site cleft. This active site cleft with its dynamic opening and closing is a prime target for protein kinase inhibitors.

Animals↗
PubMedDate not supplied

Residual disease and presence of human papillomavirus after conization.

The objective of this study was to evaluate the incidence of residual disease and the presence of human papillomavirus (HPV) after conization. Data on 53 patients with carcinoma in situ or microinvasive carcinoma who underwent hysterectomy less than 2 months after conization were examined. Seven of 53 patients (13%) had positive margins. In 4 of these 7 patients (57%), residual disease was found in the postconization hysterectomy specimen. Two of 46 patients (4%) with negative margins also had residual disease. HPV DNA was detected by PCR in 27 of 53 conization specimens and in 2 postconization hysterectomy specimens. Of 2 patients, 1 did not have residual disease. Residual disease could be present even with a negative conization margin, and HPV DNA may be found in a histologically normal cervix after conization.

Adult↗
PubMedDate not supplied

Prevalence of Alzheimer's disease and other dementing disorders in an urban community of Beijing, China.

A door-to-door two-phase study was used to investigate the prevalence of senile dementia in an urban community of Beijing. In the study population, 5,003 individuals aged 60 years and older (>/=65 years, n = 3,728) were screened at home with the Chinese version of the MMSE. Persons who screened positive for dementia, using different cutoff scores based on degree of literacy, were further evaluated using the criteria of DSM-III-R and ICD-10. Among subjects who screened positive in phase I, 134 were diagnosed as having dementia in phase II. The prevalence ratios of dementia were 2.68% in the population aged 60 years and older, and 3.49% in the population aged 65 years and older. The prevalence rates among those aged 65 years and older were 1.85% for Alzheimer's disease, 1.37% for vascular dementia and 0.27% for other dementia (including mixed dementia). The prevalence of all dementia and AD increased steeply with advancing age and was consistently higher in women, but it was not obviously higher for VaD in women. Alzheimer's disease was the commonest type of dementia. Our prevalence figures for dementia and AD are similar to those previously reported for China.

Aged↗
PubMedDate not supplied

How is modification of the DNA substrate recognized by the PvuII restriction endonuclease?

In restriction-modification systems, cleavage of substrate sites in cellular DNA by the restriction endonuclease is prevented by the action of a cognate methyltransferase that acts on the same substrate sites. The PvuII restriction endonuclease (R.PvuII) has been structurally characterized in a complex with substrate DNA (Cheng et al., 1994) and as an apoenzyme (Athanasiadis et al., 1994). We report here a structure, determined to 1.9 A resolution by crystallography, of a complex between R.PvuII and iodinated DNA. The presence of an iodine at the 5-carbon of the methylatable cytosine results in the following changes in the protein: His84 moved away from the modified base; this movement was amplified in His85 and disrupts an intersubunit hydrogen bond; and the base modification disturbs the distribution of water molecules that associate with these histidine residues and the area of the scissile bond. Considering these observations, hypotheses are given as to why a similar oligonucleotide, where a methyl group resides on the 5-carbon of the methylatable cytosine, is slowly cleaved by R.PvuII (Rice et al., 1995).

Crystallography, X-Ray↗
PubMedDate not supplied

Solvolytic formation of 1,2-dichloro-3,4-epoxybutane from butadiene monoxide under physiological conditions.

Butadiene monoxide, a presumed carcinogenic metabolite of butadiene, is stable in water or phosphate buffer, but was found to rapidly disappear from the headspace of solutions (10(-6) to 10(-4) M) in phosphate-buffered saline incubated at 37 degrees C. The process was first order with respect to monoxide concentration, with an apparent rate constant of 6.6 x 10(-4) sec-1. Mass spectrometric examination of the major product formed indicated it to be 1,2-dichloro-3,4-epoxybutane, which was confirmed by synthesis. Formation of the dichloro epoxide was linearly dependent on chloride ion concentration of the medium, but independent of dissolved oxygen. The formation of the dichloro epoxide is explained by slow solvolytic formation of a chloronium ion from butadiene monoxide, which is followed by attack of chloride ion to generate chlorine and butadiene. The chlorine is than rapidly trapped by second molecule of butadiene monoxide. This was confirmed by competitive trapping of generated chlorine by inclusion of crotyl alcohol in the incubation. A similar pathway has recently been demonstrated for reversible formation of bromine from solvolytically generated bromonium ions. The facile formation of dichloroepoxybutane under physiological conditions may be of significance in the toxicity of butadiene.

Bromine↗
PubMedDate not supplied

The urban church and cancer control: a source of social influence in minority communities.

A study was conducted to examine the efficacy of a church-based model of social influence in improving access to and participation of underserved minority women in a cervical cancer control program. The model expanded on strategies used in previous hypertension control and health promotion research. A total of 24 churches, stratified by faith tradition, were randomly selected to participate in the cancer control program from a pool of 63 churches in a defined geographic area of Los Angeles County, CA. Female parishioners ages 21 years and older were eligible to participate in cervical cancer education sessions, and screening was offered to adult women who had not had Papanicolaou tests within the last 2 years. Church participation rate was 96 percent. Thirty lay health leaders were selected by the clergy to serve as messengers, recruiters, and organizers for their respective congregations. Ninety-seven percent of these lay health leaders participated in two training sessions designed to prepare them for their leadership role. Social support structures such as child care, meals, or transportation for targeted women were organized by lay health leaders in 78 percent of the churches. A total of 1,012 women between the ages of 21 and 89 years attended educational sessions. Forty-four percent of the eligible women were targeted for screening because they had not had a Papanicolaou test within the last 2 years or had never been screened. Black women were 6.6 times more likely than Hispanics to have been screened in the past 2 years. Hispanic women were 4.2 times more likely than African Americans never to have had a Papanicolaou test or been tested in 3 or more years.Overall, 90 percent of the women targeted for screening recruitment presented for tests.Fifty-two percent of the churches initiated cancer control activities by the end of the 2-year period following the culmination of the intervention program.The findings suggest that a church-based model of social influence can leverage the participation of minority women in cervical cancer control, provide access to underserved Hispanic women in particular,and sustain cancer control activities beyond the life of an intervention program.The findings further suggest that a more discrete assessment of screening history may improve the participation levels of African American women, and that the gratis offering of screening services may adversely affect their participation rates.

Adult↗
PubMedDate not supplied

A simplified methodology for quantitation of butadiene metabolites. Application to the study of 1,3-butadiene metabolism by rat liver microsomes.

A rapid, simple extraction and GC assay procedure is described that allows quantitation of micromolar concentrations of butadiene bisoxide and 3-butene-1,2-diol in microsomal suspensions exposed to butadiene. Butane-1,4-diol is used as the internal standard. The recovery of these compounds from aqueous media was almost quantitative, and calibrations for each compound were linear from 10(-6) to 10(-3) M. In this system butadiene monoxide and crotonaldehyde can be rapidly quantitated at micromolar concentration by headspace sampling, using methanol or n-butanol as the internal standard. In addition, the synthesis and chemical characterization of diastereomeric 3,4-epoxybutane-1,2-diols are described. It is demonstrated that the epoxy diol, although not extractable from aqueous solutions by ethyl acetate, can be recovered upon evaporation of aqueous media, followed by ethyl acetate extraction. Direct GC quantitation of the epoxy diol was linear from 10(-5) to 10(-3) M. This procedure facilitated the examination of butadiene metabolism by rat liver microsomes. Exposure of microsomes to butadiene resulted in the NADPH-dependent formation of butadiene monoxide, crotonaldehyde, 3-butene-1,2-diol, and one diastereomer of 3,4-epoxybutane-1,2-diol.

Aldehydes↗
PubMedDate not supplied

Cytokine production by lymphoreticular cells from mammary tumor bearing mice: the role of tumor-derived factors.

Mammary tumor development has multiple effects on the T cell, B cell and macrophage compartments of the hosts as evidenced by the alterations in their phenotype and functions. Cytokines are known to modulate the immune system, thus a study of the production of these factors has great relevance to tumor immunity. Here we present evidence that tumor progression causes a profound dysregulation of the cytokine production by various lymphoreticular cells. Furthermore, the tumors themselves are capable of secreting factors that can directly or indirectly affect the cells of the immune system, thereby resulting in the immunosuppressive and other deleterious effects that favor the progress of the neoplastic disease.

Animals↗