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Biomedical subjects

G Gao

Publications and source records attributed to G Gao.

At least 73 records · Page 4Linked to original sources
PubMed1998

Carbamoyl-phosphate synthetase II in kinetoplastids.

Genes for carbamoyl-phosphate synthetase II (CPS II), the first enzyme of de novo pyrimidine biosynthesis, were cloned from kinetoplastids, Trypanosoma cruzi and Leishmania mexicana. T. cruzi CPS II gene encodes a protein of 1524 amino acids that encompasses the glutaminase and CPS domains, but incorporates neither aspartate carbamoyltransferase nor dihydroorotase. The residue corresponding to lysine 993 of Escherichia coli CPS, a residue that characterizes the CPS inhibited by UMP and that is replaced by tryptophan in those inhibited by UTP, is in kinetoplastids a hydrophilic glutamine, in line with the preferential inhibition by UDP of kinetoplastid CPS II.

Amino Acid Sequence↗
PubMed1998

A study of multiple biomarkers in coke oven workers--a cross-sectional study in China.

We conducted a cross-sectional molecular epidemiological study of coke oven workers exposed to the established carcinogen polycyclic aromatic hydrocarbons (PAHs) to evaluate the relationships between both traditional 'exposure markers' and a series of biomarkers, including urinary 1-hydroxypyrene as a marker of internal dose, leukocyte aromatic DNA adducts as markers of biologically effective dose, serum p53 protein as a response marker and genetic polymorphisms of cytochrome P4501A1 and glutathione S-transferase MI as susceptibility markers. Twenty-five male subjects each were randomly selected from the top, middle and bottom work areas of the oven, and the control plant. They were matched for age and smoking status. The mean levels of PAH exposure, monitored by stationary and personal samplers, and of worker urinary 1-hydroxypyrene differed significantly between the top, middle and bottom of the oven and control work areas. The highest stationary and personal PAH concentrations and 1-hydroxypyrene levels were demonstrated at the top work area. Good correlations were found between the stationary PAH levels, personal PAH levels and urinary 1-hydroxypyrene levels. No positive correlations were demonstrated between aromatic DNA adduct levels and current or cumulative PAH exposure dose. In the presence of genetic polymorphisms of cytochrome P4501A1, a positive correlation was demonstrated between aromatic DNA adducts and urinary 1-hydroxypyrene levels. There was also a significant correlation between serum p53 protein levels and the cumulated benzo[a]pyrene exposure dose. Although these biomarkers have certain limitations, they are applicable to cancer epidemiology, and may contribute to our understanding of the mechanisms of carcinogenesis.

Adult↗
PubMed1998

Replication defect of moloney murine leukemia virus with a mutant reverse transcriptase that can incorporate ribonucleotides and deoxyribonucleotides.

Reverse transcriptase (RT) plays a critical role in retrovirus replication, directing the synthesis of a double- stranded DNA copy of the viral RNA genome. We have previously described a mutant RT of the Moloney murine leukemia virus in which F155 was replaced by valine, and we demonstrated that this substitution allowed the enzyme to incorporate ribonucleotides to form RNA while still retaining its normal ability to incorporate deoxyribonucleotides to form DNA. When introduced into the viral genome, this mutation rendered the virus incapable of replication. Characterization of the mutant virus revealed that the enzyme was still active and able to synthesize minus-strand strong stop DNA and some longer products but failed to make full-length minus-strand DNA. We propose that the failure of the enzyme to complete DNA synthesis in vivo resulted from its ability to incorporate ribonucleotides into the products, which served as inhibitors for DNA synthesis. We also tested seven other amino acid residues for their abilities to substitute for F155 in virus replication; of these, only tyrosine could support virus replication. In an attempt to select for second-site suppressor mutations, the F155V mutant was subjected to random mutagenesis and was used as a parent for the isolation of revertant viruses. Two independent revertants were found to have changed the valine residue at position 155 back to the wild- type phenylalanine. These results suggest that an aromatic ring at this position is important for virus replication.

3T3 Cells↗
PubMed1998

[Microsurgical repair of defects of soft tissue and infected wounds of extremities].

A study was carried out to observe the application of microsurgical technique in the repair defects of soft tissue and infected wounds of extremities. Eighty-three patients with soft tissue defects and infected wounds of extremities were treated by either transferring of vascularized cutaneous flap or transplantation of myocutaneous flap with vascular anastomosis. The result showed that eighty-three patients had gained success after a follow-up of 6 months to 4 years. It was concluded that soft tissue defects and infected wounds of extremities should be repaired as early as possible. Selecting the donor flap near the recipient site was of first choice. The method used for repair should be simple and easily applicable rather these very complicated one. The success depended on the correct treatment of local conditions, resonable design of donor flap and close monitoring after operation.

Adolescent↗
PubMed1998

[Feasibility study of laser-induced fluorescence (LIF) spectrum for diagnosis of colon cancer].

OBJECTIVE: To study the usefulness of laser-induced fluorescence (LIF) spectrum for diagnosis of colon cancer. METHODS: Nitrogen laser, wavelength 337 nm, optical multichannel analyzer (OMA III) were used to demonstrate LIF spectra. A standard spectrum of LIF of colon cancer was used to analyse that of 51 surgically removed colon specimens and the results were compared with pathological findings. RESULTS: Compared with pathological findings, LIF spectrum examination had 80.0% sensitivity, 100% specificity, with positive predictive value of 100%, negative predictive value of 83.9% and accuracy of 90.2% for the diagnosis of colon cancer, respectively. CONCLUSION: Laser-induced fluorescence (LIF) spectrum of colon is of use in the diagnosis of colon cancer.

Colonic Neoplasms↗
PubMed1998

[Chemical constituents of the leaves of Crataegus scabrifolia (Franch.) Rehd].

OBJECTIVE: To explore the medicinal resources of Crataegus and seek compounds with pharmaceutical effects. METHOD: Column chromatography was employed for the isolation and purification of constituents and the structures were elucidated by spectral analysis and chemical evidence. RESULT: Six compounds were obtained and identified as rutin, hyperoside, vitexin, ursolic acid, daucosterol, and nonacosanol. CONCLUSION: The main constituents of the leaves of Crataegus scabrifolia are flavonoids.

Crataegus↗
PubMed1998

[Determination of flavonoids and quality evaluation of Chinese traditional drug "puhuang"].

This paper deals with the determination of flavonoids and quality evaluation of Chinese Typha. Four species, viz. Typha angustata, T. angustifolia, T. davidiana and T. latifolia and eight commercial samples of Chinese traditional drug "Puhuang" were collected. Five flavonoids in pollen, filaments, female flowers and leaves were determined by HPLC using mu-Bondapak C18 column, water--isopropanol--tetrahydrofuran = 83.5:14:2.5, as mokile phase and detected at 287 nm). The qualities of different Typha species and commercial "Puhuang" samples have been compared, and the criteria for their quality control were also discussed.

Chromatography, High Pressure Liquid↗
PubMed1997

Differential expression of cyclic nucleotide phosphodiesterase 3 and 4 activities in human T cell clones specific for myelin basic protein.

Little is known concerning the relative distribution and function of the different cyclic nucleotide phosphodiesterases (PDEs) in lymphocytes. Recent reports, however, have indicated that specific PDE4 inhibitors were effective in treatment of experimental allergic encephalomyelitis, an animal model of multiple sclerosis. The therapeutic effect of PDE4 inhibitors is thought to be related to inhibition of autoreactive CD4+ T cells specific for myelin basic protein (MBP) or other myelin proteins. Human autoreactive CD4+ T lymphocyte clones (TCC), specific for the immunodominant MBP epitope (amino acids 83-99), contain PDE3 and PDE4, two PDEs that exhibit a high affinity for cAMP. Amplification of TCC mRNA by reverse transcription-PCR indicated that TCC PDE3 mRNA was of the PDE3B, not PDE3A, subtype. Different TCC contained different proportions of PDE3 and PDE4, and their activities increased during Ag (MBP) stimulation. Specific PDE3 (cilostamide) and PDE4 (rolipram) inhibitors suppressed [3H]thymidine incorporation in TCC. Since it is believed that many autoimmune diseases are at least partially mediated by autoreactive CD4+ T cells, these observations may have important implications not only for the treatment of multiple sclerosis but also for other autoimmune diseases.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1997

Conferring RNA polymerase activity to a DNA polymerase: a single residue in reverse transcriptase controls substrate selection.

The traditional classification of nucleic acid polymerases as either DNA or RNA polymerases is based, in large part, on their fundamental preference for the incorporation of either deoxyribonucleotides or ribonucleotides during chain elongation. The refined structure determination of Moloney murine leukemia virus reverse transcriptase, a strict DNA polymerase, recently allowed the prediction that a single amino acid residue at the active site might be responsible for the discrimination against the 2'OH group of an incoming ribonucleotide. Mutation of this residue resulted in a variant enzyme now capable of acting as an RNA polymerase. In marked contrast to the wild-type enzyme, the K(m) of the mutant enzyme for ribonucleotides was comparable to that for deoxyribonucleotides. The results are consistent with proposals of a common evolutionary origin for both classes of enzymes and support models of a common mechanism of nucleic acid synthesis underlying catalysis by all such polymerases.

Binding Sites↗
PubMed1997

Fusion of phospholipid vesicles induced by the ribosome inactivating protein saporin.

The single chain ribosome-inactivating protein Saporin-S6 (SO-6) induces the fusion of acid phospholipid vesicles. The extent of fusion was measured by resonance energy transfer assay between the N-(7-nitro-2-1,3-benzoxadiazol-4-yl)-dimyristoylphosphatidyl lithanolamine (NBD-PE)(donor) and N-(lissamine rhodamine B sulphonyl)-diacylphoshaidylethanolamine (Rh-PE) (acceptor) incorporated in the vesicle. The saturated lipid/protein molar ratio is approx. 100:1. The time course of fusion of vesicles induced by the protein showed that the process was completed within 10 minutes, and the size of the particles in the medium was enlarged which conforms the occurrence of the fusion occurring. The fusion is temperature dependent and the liquid-crystalline state lipid is more apt to fuse than the gel phase lipid. The effect of SO-6 is also dependent on ionic strength and pH, high salt concentration and basic pH may abolish fusion, which suggests that both electrostatic and hydrophobic components may be involved in the process.

Hydrogen-Ion Concentration↗
PubMed1997

[Measurement of skin area of expansion and defect on scalp].

The skin expander has been widely used to produce extra skin by the plastic surgeon, but there is no a scientific method for measuring the skin area of external expansion. The plastic surgeon usually do not know exactly whether the skin area of expansion more or less than the skin area of defect. A morphologic measure method was developed to figure out accurately the area of expansion and the area of defect separately. Clinical application has proved that the method can help the plastic surgeon know the wanted skin area of expansion in practice before operation.

Adult↗
PubMed1997

[P53 protein expression in malignant germ cell tumor of ovary and its relationship with clinical course and prognosis].

To study the relationship of P53 protein expression with clinical course and prognosis in malignant germ cell tumor of ovary P53 protein expression was examined by immunohistochemical ABC methods in 82 cases of the neoplasm and 20 cases of normal ovary tissue. The results showed that no expression of P53 protein was detected in normal ovarian tissue. The total expression rate of P53 protein was 24.39% in neoplasm, and the expression was not significantly correlated with the different histological types of neoplasm. The study however found that the protein expression of p53 gene was significantly correlated with the clinical stages and prognosis of the neoplasm.

Choriocarcinoma↗
PubMed1996

Regulation of 5'-AMP-activated protein kinase activity by the noncatalytic beta and gamma subunits.

The mammalian 5'-AMP-activated protein kinase is a heterotrimer consisting of an alpha catalytic subunit and beta and gamma noncatalytic subunits, each of which is represented in a larger isoprotein family, related to the SNF1 kinase and its interacting proteins in yeast. In this study, we have used mammalian cell transfection to compare the activities of the two alpha subunit isoforms, alpha-1 and alpha-2, and to study the influence of the noncatalytic subunits on enzyme subunit association and activity. Expression of epitope-tagged protein subunits in COS7 cells indicates detectable but low level kinase activity for each of the two catalytic alpha subunits. Co-expression of alpha subunits with the beta or gamma subunits modestly increases kinase activity accompanied by the formation of alpha/beta or alpha/gamma heterodimers. Co-expression of all three subunits, however, is accompanied by a 50-110-fold increase in kinase activity with the formation of a heterotrimeric complex. In addition to binding of each noncatalytic subunit to the alpha subunit, the beta and gamma subunits bind to each other, likely resulting in a more stable heterotrimeric complex. The increase in kinase activity associated with expression of this heterotrimer is due both to an increase in enzyme-specific activity (units/enzyme mass) and to an apparent enhanced alpha subunit expression. Co-expression of a catalytically defective alpha subunit or the beta/gamma-binding COOH-terminal domain of the alpha subunit results in reduced heterotrimeric kinase activity. The synergistic positive regulatory roles for both the noncatalytic beta and gamma subunits of 5'-AMP-activated protein kinase contrasts with the Snf1p kinase, where only heterodimers of Snf1p and Snf4p seem to be required for maximum kinase activity.

AMP-Activated Protein Kinases↗
PubMed1996

Receptor specificity of the fibroblast growth factor family.

Fibroblast growth factors (FGFs) are essential molecules for mammalian development. The nine known FGF ligands and the four signaling FGF receptors (and their alternatively spliced variants) are expressed in specific spatial and temporal patterns. The activity of this signaling pathway is regulated by ligand binding specificity, heparan sulfate proteoglycans, and the differential signaling capacity of individual FGF receptors. To determine potentially relevant ligand-receptor pairs we have engineered mitogenically responsive cell lines expressing the major splice variants of all the known FGF receptors. We have assayed the mitogenic activity of the nine known FGF ligands on these cell lines. These studies demonstrate that FGF 1 is the only FGF that can activate all FGF receptor splice variants. Using FGF 1 as an internal standard we have determined the relative activity of all the other members of the FGF family. These data should serve as a biochemical foundation for determining developmental, physiological, and pathophysiological processes that involve FGF signaling pathways.

Alternative Splicing↗
PubMed1996

Non-catalytic beta- and gamma-subunit isoforms of the 5'-AMP-activated protein kinase.

The mammalian 5'-AMP-activated protein kinase (AMPK) is a heterotrimeric protein consisting of alpha-, beta-, and gamma-subunits. The alpha-subunit is the catalytic subunit and is related to the yeast Snf1p kinase. In this study, we report the cloning of full-length cDNAs for the non-catalytic beta- and gamma-subunits. The rat liver AMPK beta-subunit clone predicts a protein of 30,464 Da, which is related to the Sip1p, Sip2p, and Gal83p subfamily of yeast proteins that interact with Snf1p and are involved in glucose regulation of gene expression. The AMPK beta-subunit, when expressed in bacteria and in mammalian cells, migrates anomalously on SDS gels at an apparent molecular mass of 40 kDa. Rat and human liver AMPK gamma-subunit clones predict a protein of 37,577 Da (AMPK-gamma1), which is related to the yeast Snf4p protein that copurifies with Snf1p and to a larger family of other human AMPK gamma-isoforms. The mRNAs for both AMPK- beta and AMPK-gamma1 are widely expressed in rat tissues, consistent with a broad role for AMPK in cellular regulation. These data reveal a mammalian multisubunit protein kinase strikingly similar to the multisubunit glucose-sensing Snf1 kinase complex. The identification of isoform families for the AMPK subunits indicates the potential diversity of the roles of this highly conserved signaling system in nutrient regulation and utilization in mammalian cells.

AMP-Activated Protein Kinases↗
PubMed1996

Mammalian AMP-activated protein kinase subfamily.

The mammalian 5'-AMP-activated protein kinase (AMPK) is related to a growing family of protein kinases in yeast and plants that are regulated by nutritional stress. We find the most prominent expressed form of the hepatic AMPK catalytic subunit (alpha 1) is distinct from the previously cloned kinase subunit (alpha 2). The alpha 1 (548 residues) and alpha 2 (552 residues) isoforms have 90% amino acid sequence identity within the catalytic core but only 61% identity elsewhere. The tissue distribution of the AMPK activity most closely parallels the low abundance 6-kilobase alpha 1 mRNA distribution and the alpha 1 immunoreactivity rather than alpha 2, with substantial amounts in kidney, liver, lung, heart, and brain. Both alpha 1 and alpha 2 isoforms are stimulated by AMP and contain noncatalytic beta and gamma subunits. The liver alpha 1 isoform accounts for approximately 94% of the enzyme activity measured using the SAMS peptide substrate. The tissue distribution of the alpha 2 immunoreactivity parallels the alpha 2 8.5-kilobase mRNA and is most prominent in skeletal muscle, heart, and liver. Isoforms of the beta and gamma subunits present in the human genome sequence reveal that the AMPK consists of a family of isoenzymes.

Amino Acid Sequence↗