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Biomedical subjects

L Feng

Publications and source records attributed to L Feng.

At least 253 records · Page 14Linked to original sources
PubMed1992

[Epidemiological study of selective IgA deficiency among 6 nationalities in China].

The frequency of selective IgA deficiency (SIgAD) was determined in 33,171 Chinese distributed in six nationalities by Ouchterlony's double diffusion with 5 mg/dl as the limit of detection. Those who were found IgA-deficient were retested by single radial diffusion technique. Gel diffusion analysis of sera revealed apparent lack of IgA in 8 samples, all with normal levels of IgG and IgM (age-matched). The incidence was 0.024% (1:4,100). The incidences among the six nationalities were Han 1:2,600, Hui 1:5,000, Mongolia 1:2,700, Tujia 1:4,300, Zhuang 0:5,300, and Bai 1:4,800. All of the individuals, who had low levels of IgA or no IgA detectable, were below 16 years of age. Of these, 2 sera were autoantibody (anti-smooth muscle antibody) positive Delayed hypersensitivity skin tests were negative in one individual. The chief clinical manifestations were those of respiratory tract infections, of which about 50% were in subclinical state.

Adolescent↗
PubMed1992

Establishment of hybridoma cell line secreting specific monoclonal antibodies against turnip mosaic virus and analysis of properties of the McAb.

Monoclonal antibodies (McAb) of hybridomas derived from the fusing of the mouse splenocytes immunized by TuMV with BALB/c mouse myeloma cells (SP2/0-Ag14). Five kinds of hybridoma cell line were produced by indirect-ELISA screening and cloning three times with limiting dilution. Four kinds of hybridoma produced antibodies respectively reactive to TuMV C1, C3, C4 and C5. One kind was reactive to all five strains of TuMV. In indirect-ELISA and sandwich-ELISA tests, TuMV specific monoclonal antibodies did not react with CaMV, CMV, TMV, PVX, and PVY. Antibody titers of ascitic fluids were about 1:256,000 to 2,048,000 in indirect-ELISA. The biological, physical, and chemical properties of the hybridoma cell lines and McAb were identified. The identification of TuMV strains, the specificity and stability of McAb, the coat proteins, and the antigenic site of TuMV were discussed and analyzed with SDS-PAGE and western-blotting.

Animals↗
PubMed1992

A strategy for isolating differentiation-inducing complementary DNAs from human esophageal cancer cell line treated with retinoic acid.

Treatment of the human esophageal cancer cell line EC8712 with retinoic acid (RA) stopped the cell growth significantly and gave rise to terminal differentiation of the cells characterized by increased expression of involucrin gene. Two cDNA libraries were constructed from the parental and RA-treated cells respectively. Repeated subtractive hybridization of single-stranded plasmid DNA prepared from pooled colonies of cDNA library of the parental cells with cDNA probe generated from the RA-treated cells exhausted sequences common to both libraries of the cell. The unhybridized cDNA probe represented, therefore, the genes activated after RA-treatment. By using these enriched cDNAs as probe to screen the cDNA library constructed from the RA-treated cells thirty-nine positive colonies were obtained, of which two were specifically due to RA-induction. One of these two cDNA clones, designated as pRA538, has undergone further analysis and shown differentiation-inducing effect on parental cancer cells. A novel strategy for cloning genes involved in terminal differentiation of cancer cells is developed.

Carcinoma, Squamous Cell↗
PubMed1991

[Quality standard of kaixiong shunqi pills].

This paper adds TLC identification of binglang and other three cruds drugs to the quality control of kakxiong shunqi pills incorporated in Chinese Pharmacopoeia. The contents of magnolol and honokinol were determined by TLC scanning. The method is simple, rapid accurate, and useful in controlling the quality of kaixiong shunqi pills.

Biphenyl Compounds↗
PubMed1990

Comparison of chemical reactivity, cytotoxicity, interstrand cross-linking and DNA sequence specificity of bis(platinum) complexes containing monodentate or bidentate coordination spheres with their monomeric analogues.

The properties of a new bis(platinum) complex containing two monodentate coordination spheres, [(trans-PtCl(NH3)2)2H2N(CH2)4NH2]Cl2 (1,1/t,t), are reported. Comparison is made with respect to chemical reactivity, in vitro biological activity in murine and tumor cells, DNA conformational changes, cross-linking efficiency, and sequence specificity between this complex and the previously reported complex containing two bidentate platinum atoms, [(Pt(mal)(NH3))2H2N(CH2)4NH2] (2,2/c,c), as well as with their respective monomeric analogues, [PtCl(dien)]Cl and cis-[PtCl2(NH3)2](cis-DDP). While both bis(platinum) complexes are active against cis-DDP-resistant cells, the monodentate bis(platinum) complex (1,1/t,t) has a lower resistance factor than the complex with bidentate coordination spheres (2,2/c,c). More importantly, this property is repeated in a human ovarian carcinoma cell line. DNA-binding studies show that DNA interstrand cross-linking is more efficient for the 1,1/t,t complex. DNA sequencing studies employing the exonuclease activity of T4-polymerase demonstrate that there are a variety of binding sites; some are common to all complexes and some common to both bis(platinum) complexes, while the monodentate 1,1/t,t species also reacts at unique sites, not attacked by any of the other complexes studied. The circular dichroism of CT DNA modified by the 1,1/t,t complex is also unique and is not seen for any of the other agents.

Animals↗
PubMed1990

Nucleotide sequence of a gene which enhances the activity of glyoxalase I in Saccharomyces cerevisiae.

A gene whose product enhances glyoxalase I activity in yeast Saccharomyces cerevisiae cells was cloned as a 6-kbp DNA fragment in the vector YEp13. The DNA fragment was subcloned in approximately 2 kbp and its base sequence determined. An open reading frame with 318 nucleotide pairs (encoding 106 amino acids) was found. According to Northern blotting analysis, the yeast transformed with the hybrid plasmid harboring the 2-kbp fragment yielded two different transcripts. From the DNA sequence of the fragment, it is deduced that the gene product would contain seven cysteine residues, five of which would be located near the carboxy terminus of the peptide.

Amino Acid Sequence↗
PubMed1989

Yeast translation initiation suppressor sui2 encodes the alpha subunit of eukaryotic initiation factor 2 and shares sequence identity with the human alpha subunit.

Genetic reversion of HIS4 initiator codon mutations in yeast has identified three unlinked genes, sui1, sui2, and SUI3 (suppressors of initiator codon mutations), which when mutated confer the ability to initiate translation at HIS4 despite the absence of an AUG start codon. We have previously demonstrated that the SUI3 gene encodes the beta subunit of the eukaryotic initiation factor 2 (eIF-2) and that mutations at a Zn(II) finger motif of SUI3 alter the start site selection process in yeast. In this report, molecular and biochemical characterizations show that the sui2 suppressor gene encodes the alpha subunit of eIF-2. The amino acid sequence of sui2 is 58% homologous to that encoded by the cDNA of the human eIF-2 alpha. Mutations in the sui2 suppressor alleles occur in the amino-terminal portion of the protein and change amino acids that are identical at the same relative position in the yeast and human proteins. Protein sequence analysis shows that a sui2 mutant yeast strain allows initiation at a UUG codon in the absence of an AUG codon at HIS4. These data further suggest that eIF-2 is an important component of the preinitiation complex that mediates ribosomal recognition of a start codon during the scanning process.

Amino Acid Sequence↗
PubMed1989

Mu heavy chains can associate with a pseudo-light chain complex (psi L) in human pre-B cell lines.

In pre-B cells, the earliest identifiable stage of B cell differentiation, there is an asynchrony of immunoglobulin chain expression in that mu heavy chains are synthesized in the absence of light chain synthesis. These mu chains largely remain intracellular and are degraded. Here we demonstrate that a fraction of mu chains in human pre-B cell lines can reach the surface in association with three pre-B-specific proteins with relative molecular masses of 22, 18, and 16 kd, which we term collectively the pseudo-light chain complex, psi L. This association generates a multimeric complex, mu 2-psi L. Two of the psi L proteins (22 and 16 kd) are lambda-immunoreactive and form disulfide bonds with mu chains, suggesting that they are closely related to conventional lambda light chains. The 18 kd psi L species is a non-covalently-associated member of the complex. The expression of mu-psi L complexes on the surface of pre-B cells could have a functional role in the control of pre-B growth and differentiation by the hematopoietic microenvironment.

B-Lymphocytes↗
PubMed1988

tRNAi(met) functions in directing the scanning ribosome to the start site of translation.

The mechanism by which the scanning ribosome recognizes the first AUG codon nearest the 5' end of eukaryotic messenger RNA has not been established. To investigate this an anticodon change (3'-UCC-5') was introduced into one of the four methionine initiator (tRNAi(met) genes of Saccharomyces cerevisiae. The ability of the mutant transfer RNA to restore growth properties to his4 initiator codon mutant yeast strains in the absence of histidine was then assayed. Only the complementary codon, AGG, at the his4 initiator region supported His+ growth. The mutant transfer RNA also directed the ribosome to initiate at an AGG placed in the upstream region of the his4 message. Initiation at this upstream AGG precluded initiation at a downstream AGG in accordance with the "scanning" model. Therefore, an anticodon: codon interaction between tRNAi(met) as part of the scanning ribosome and the first AUG must function in directing the ribosome to the eukaryotic initiator region.

Anticodon↗
PubMed1988

Scanning tunnelling microscopic images of amino acids.

We present images of amino acids adsorbed on highly orientated pyrolytic graphite (HOPG) obtained with the scanning tunnelling microscope (STM) in air. Individual molecules can be observed although the majority of adsorbates appear to form clusters. In the case of leucine, methionine, and tryptophan, two molecules often associate together to form a dimer. Single or dimer glycine molecules were not seen, but a cluster of a number of them was observed. The various adsorbed states may be related to the different interactions between the amino acids and the graphite surface. The mechanism of image formation of the amino acids is probably related to charge transfer mechanisms.

Adsorption↗
PubMed1987

[Modification of esophageal epithelium DNA in the human fetus by N-nitrosomethylbenzylamine (NMBzA)].

Human fetal esophageal epithelium, after being exposed to NMBzA, was found to contain O6-methyldeoxyguanine (O6-MedG), a NMBzA-modified DNA adduct, in tissue DNA by radioimmunoassay and monoclonal antibody, which is highly specific to O6-MedG. The highest level of O6-MedG was 58.83 pMol/mg DNA after adding 5.0 mM NMBzA in vitro. The level of O6-MedG and the concentration of NMBzA followed the dose-effect relationship. O6-MedG could be eliminated from DNA by normal human fetal esophageal epithelium. About 50% of O6-MedG was cleared away in the first 1-2 hours during the post-treatment incubation, which was followed by a slower phase of elimination with 18% left in 24 hours. The results indicate that the human fetal esophageal epithelium can metabolically activate NMBzA in vitro and form O6-MedG, which, as well known, can cause mutagenesis and carcinogenesis and, hence, may most likely be related to the development of human esophageal cancer.

Carcinogens↗
PubMed1986

Relevance of N-nitrosamines to esophageal cancer in China.

Studies on the relevance of the N-nitrosamines to esophageal cancer in China are reviewed. Esophageal cancer is a complex and multifactorial problem. Although a causal association between nitrosamines exposure and esophageal cancer in China has not yet been rigorously established, exposure of Lin-Xian subjects to nitrosamines either directly or as a result of their in vivo formation has been detected in our study. Several N-nitrosamines (NDMA, NDEA, NMBzA, NPyr, NPip, and NSAR) in gastric juice collected from Lin-Xian inhabitants have been detected. A correlation was found between the lesions of esophageal epithelium and the amount of nitrosamines present. In addition, the amounts of N-nitrosamino acids (N-nitrosoproline, N-nitrosothiazolidine 4-carboxylic acid, NSAR, and nitrates) excreted in 24-hr urine of subjects in Lin-Xian were significantly higher than those in Fan-Xian, indicating a higher exposure to N-nitroso compound and their precursors of the inhabitants in the high-risk area. The effect of nitrosamines on human esophagus has been investigated at the cellular levels. The amounts of O6-MedG in DNA of esophageal or stomach mucosa of patients from Lin-Xian were higher than that from Europe (Lyon and Essen). The presence of O6-MedG in the human fetal esophagus cultured with NMBzA was also detected. These findings indicate that the elevated levels of O6-MedG in esophageal DNA could be the result of a recent exposure to N-nitroso compounds or a genetically determined reduced cellular capacity for repair of O6-MedG from DNA. The hyperplasia was induced in the esophagus of human fetus that cultured with NMBzA for 2 weeks to 2 months. The intervention studies of esophageal cancer in Lin-Xian have been pursued. Intake of moderate doses of ascorbic acids by Lin-Xian subjects effectively reduced the urinary levels of N-nitrosamino acids to those found in un-dosed subjects in the low-risk area. If N-nitroso compounds are formed in vivo and are among the causative factors of esophageal cancer in Lin-Xian, ascorbic acid appears to be effective in lowering the body burden of these carcinogenic compounds. Thus, the plan of chemoprevention is carried out in Lin-Xian.

Ascorbic Acid↗