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Biomedical subjects

Li Zheng

Publications and source records attributed to Li Zheng.

68 records · Page 4Linked to original sources
PubMed2003

[Creating the model county to promote the prevention of blindness in Zhejiang Province].

OBJECTIVE: To develop a system of enhancing work efficiency in prevention of blindness in Zhejiang province by creating the Model County in prevention of blindness. METHODS: Twenty counties were selected in the whole Zhejiang province to serve as the candidates of the Model County in prevention of blindness in 1996 - 1998. The activities for prevention of blindness were conducted in these counties according to the five standards of the Model County in prevention of blindness established by the National Committee for Prevention of Blindness. The Model County in prevention of blindness was awarded only after checking and accepting by the authorities in county, provincial and national levels. RESULTS: The effective way for creating the Model County in prevention was as follows: the local government put the prevention of blindness in the list of the priorities, the local committee for prevention of blindness was established, the three level network for prevention of blindness was established, the eye care workers were trained, the necessary equipment was provided. After the efforts for three years, seven counties were awarded as the Model County in prevention of blindness. In addition, Shaoxing Prefecture city became Model City in prevention of blindness. A strong effort was made to promote the activities for prevention of blindness during 1996 to 1998 in the other thirteen counties. The number of eye doctors increased from 602 into 1 850. There were two folds increase in the number of equipment availability, for example, slit lamp and ophthalmic microscope. The annual number of cataract surgeries was about 20 000. CONCLUSION: It appears to be a good approach to create the Model County to promote the prevention of blindness.

Blindness↗
PubMed2003

[Progress on industrial ecological studies of dry-cleaning process].

The safety assurance of dry cleaning solvent and rational residue criteria of volatile hazardous organic compounds in clothes are vital to clean production and green service in dry cleaning industry. Therefore, the environmental behavior of the enterprises should be regulated and assurance to the human health and the environment through the combination of environmental technologies and economic instruments. Progress on industrial ecological studies of dry-cleaning process was reviewed and the protective strategies and approaches of environmental safety technologies to the sustainable development of dry cleaning were put forward in this paper.

Environmental Health↗
PubMed2002

Functional alterations of human exonuclease 1 mutants identified in atypical hereditary nonpolyposis colorectal cancer syndrome.

Hereditary Nonpolyposis Colorectal Cancer (HNPCC) is a genetically heterogeneous disorder caused by germ-line mutations in one of several DNA mismatch repair (MMR) genes, most commonly in hMSH2 and hMLH1. Human exonuclease 1 (hExo1) possesses both 5'exonuclease and flap endonuclease activities and plays a role in DNA repair, recombination, and replication. The enzyme interacts with MMR proteins, hMsh2, hMlh1, and hMsh3. Recently, eight missense mutations in hEXO1 were identified in atypical HNPCC patients, who have been screened to be negative for hMSH2, hMLH1, and hMSH6 mutations. To address the question of whether these mutations cause susceptibility to HNPCC, in vitro nuclease activity and protein-protein interaction assays were performed in this study. We found that two mutants, E109K and L410R, lost their exonuclease activities while retaining their capacity to bind to the DNA substrate. Three other mutants, P640S, G759E, and P770L, displayed a reduced capacity to interact with hMsh2. The combination of these three point mutations leads to the binding capacity with hMsh2 to nearly zero. Evidence made available in this study sheds light on the pathogenesis of HNPCC, perhaps initiated by an additional MMR gene, hEXO1.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Molecular affinity and permeability of different molecular weight chitosan membranes.

Membranes were prepared from chitosan with different molecular weights by a casting method. The molecular affinity and permeability of the membranes for sodium chloride, glucose, tyrosine, and bovine serum protein were measured at 4 degrees C and pH 7. The molecular permeability of the chitosan membranes was inversely related to molecular weight. All prepared membranes showed a molecular affinity to bovine serum protein. The higher the molecular weight of chitosan membrane, the higher the affinity and the lower permeability of the membrane to bovine serum protein.

Blood Proteins↗
PubMed2002

Suppression of Saccharomyces cerevisiae rad27 null mutant phenotypes by the 5' nuclease domain of Escherichia coli DNA polymerase I.

RNA primer removal from Okazaki fragments during lagging-strand replication and the excision of damaged DNA bases requires the action of structure-specific nucleases, such as the mammalian flap endonuclease 1 (FEN-1). This nuclease contains two conserved motifs enriched with acidic amino acid residues that are important for catalytic function. Similar motifs have been identified in nucleases found in viruses, archebacteria, eubacteria, and in eukaryotes ranging from yeast to humans. Unique among these proteins, the putative FEN-1 homologue in Escherichia coli is contained within the N-terminal region of the DNA polymerase I (PolN). To demonstrate that the cellular functions of FEN-1 reside in PolN, we cloned and expressed the amino terminal domain (323 amino acid residues) of PolI in a Saccharomyces cerevisiae strain lacking the FEN-1 homologue RAD27. Overexpression of PolN suppressed, to varying degrees, phenotypes associated with a rad27 null strain. These include temperature sensitivity, Okazaki fragment processing, a mutator phenotype, a G2/M cell cycle arrest, minichromosome loss, and methyl methane sulfonate sensitivity. We purified Rad27 and PolN proteins in order to determine whether differences in their intrinsic nuclease activities or interaction with proliferating cell nuclear antigen (PCNA) could explain the partial suppression of some phenotypes. We found that the in vitro nuclease activities of Rad27 were more potent than those of PolN and the activity of Rad27, but not PolN, was stimulated by PCNA. We conclude that the N-terminal nuclease domain of E. coli polymerase I encodes a functional homologue of FEN-1.

Conserved Sequence↗
PubMed2002

Distinct roles of two Mg2+ binding sites in regulation of murine flap endonuclease-1 activities.

Removal of flap DNA intermediates in DNA replication and repair by flap endonuclease-1 (FEN-1) is essential for mammalian genome integrity. Divalent metal ions, Mg(2+) or Mn(2+), are required for the active center of FEN-1 nucleases. However, it remains unclear as to how Mg(2+) stimulates enzymatic activity. In the present study, we systemically characterize the interaction between Mg(2+) and murine FEN-1 (mFEN-1). We demonstrate that Mg(2+) stimulates mFEN-1 activity at physiological levels but inhibits the activity at concentrations higher than 20 mM. Our data suggest that mFEN-1 exists as a metalloenzyme in physiological conditions and that each enzyme molecule binds two Mg(2+) ions. Binding of Mg(2+) to the M1 binding site coordinated by the D86 residue cluster enhances mFEN-1's capability of substrate binding, while binding of the metal to the M2 binding site coordinated by the D181 residue cluster induces conformational changes. Both of these steps are needed for catalysis. Weak, nonspecific Mg(2+) binding is likely responsible for the enzyme inhibition at high concentrations of the cation. Taken together, our results suggest distinct roles for two Mg(2+) binding sites in the regulation of mFEN-1 nuclease activities in a mode different from the "two-metal mechanism".

Amino Acid Substitution↗
PubMed2002

Activation of plant phospholipase Dbeta by phosphatidylinositol 4,5-bisphosphate: characterization of binding site and mode of action.

Hydrolysis of phospholipids by plant phospholipase Dbeta (PLDbeta) requires phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]. Here we show that PLDbeta is stimulated by different polyphosphoinositides, among which PI(4,5)P2 is most effective. On the basis of amino acid sequence analysis, PI(4,5)P2 binding assay, and protein engineering studies, we have identified in the catalytic region of PLDbeta a new PI(4,5)P2 binding region (PBR1), which is conserved in eukaryotic PLDs. PBR1 is a second domain besides the previously characterized N-terminal C2 domain of PLDbeta which also binds PI(4,5)P2. Submillimolar levels of calcium ions, while inhibiting PI(4,5)P2 binding by the C2 domain, enhanced the affinity of PBR1 for that phosphoinositide. Substrate binding by PLDbeta was promoted by PI(4,5)P2-bound PBR1. Isolated, recombinant PBR1 bound PI(4,5)P2 specifically and in a saturable manner. Deletion of PBR1 from PLDbeta or mutation of the conserved basic amino acid residues in PBR1 (K437G/K440G) abolished the enzymatic activity. Circular dichroism spectroscopy revealed a conformational change caused by PI(4,5)P2 binding to the catalytic region of PLD. The conformational change apparently helps in the recruitment of the substrate to the active site of the enzyme. The results taken together allow us to describe an anchorage-scooting model for the synergistic activation of PLDbeta by PI(4,5)P2 and Ca2+.

Amino Acid Sequence↗
PubMed2002

MST12 regulates infectious growth but not appressorium formation in the rice blast fungus Magnaporthe grisea.

In the rice blast fungus Magnaporthe grisea, a mitogen-activated protein kinase gene, PMK1, is known to regulate appressorium formation and infectious hyphae growth. Since PMK1 is homologous to the FUS3 and KSS1 genes that regulate the transcription factor STE12 in yeast, we functionally characterized the STE12 homologue in M. grisea (MST12). A polymerase chain reaction-based approach was used to isolate the MST12 gene that is homologous to yeast STE12. Four mst12 deletion mutants were isolated by gene replacement. No obvious defect in vegetative growth, conidiation, or conidia germination was observed in mst12 mutants. However, mst12 mutants were nonpathogenic on rice and barley leaves. In contrast to pmk1 mutants that did not form appressoria, mst12 mutants produced typical dome-shaped and melanized appressoria. However, the appressoria formed by mst12 mutants failed to penetrate onion epidermal cells. When inoculated through wound sites, mst12 mutants failed to cause spreading lesions and appeared to be defective in infectious growth. These data indicate that MST12 may function downstream of PMK1 to regulate genes involved in infectious hyphae growth. A transcription factor or factors other than MST12 must exist in M. grisea and function downstream from PMK1 for appressorium formation.

Amino Acid Sequence↗
PubMed2002

Two novel fungal virulence genes specifically expressed in appressoria of the rice blast fungus.

The PMK1 mitogen-activated protein kinase gene regulates appressorium formation and infectious hyphae growth in the rice blast fungus. To further characterize this mitogen-activated protein kinase pathway, we constructed a subtraction library enriched for genes regulated by PMK1. Two genes identified in this library, GAS1 and GAS2, encode small proteins that are homologous with gEgh16 of the powdery mildew fungus. Both were expressed specifically during appressorium formation in the wild-type strains, but neither was expressed in the pmk1 mutant. Mutants deleted in GAS1 and GAS2 had no defect in vegetative growth, conidiation, or appressoria formation, but they were reduced in appressorial penetration and lesion development. Interestingly, deletion of both GAS1 and GAS2 did not have an additive effect on appressorial penetration and lesion formation. The GAS1-green fluorescent protein and GAS2-green fluorescent protein fusion proteins were expressed only in appressoria and localized in the cytoplasm. These two genes may belong to a class of proteins specific for filamentous fungi and function as novel virulence factors in fungal pathogens.

Amino Acid Sequence↗
PubMed2002

Irradiation-induced apoptosis of mouse bone marrow stromal cells.

OBJECTIVE: To study the apoptotic patterns of bone marrow stromal cells (BMSCs) after irradiation. METHODS: Apoptosis of BMSCs induced by (60)Co gamma irradiation was detected by both flow cytometry and electron microscopy. RESULTS: Compared with normal control group, no manifest changes in the apoptosis ratio occurred in BMSCs after 50 Gy irradiation (P>0.05) as demonstrated by flow cytometry. Four hours after 100 Gy irradiation, manifest changes in apoptosis ratio of BMSCs were observed (P<0.01), reaching the peak 20 h later. Similar apoptotic patterns occurred in BMSCs exposed to irradiation of 200 Gy (P>0.05), only the apoptosis ratio was slightly higher. CONCLUSION: Irradiation of proper dose may induce apoptosis in vitro in BMSCs that possess strong resistance to irradiation.

Animals↗
PubMedDate not supplied

An improved straight-line fitting method for analyzing pumping test recovery data.

Theis (1935) derived an exact solution for the residual drawdown in a well after the cessation of a pumping test by summing two drawdowns: one (s1), caused by imaginary continuation of the original pumping and the other (s2), due to an imaginary injection at the same constant rate. We approximated the Theis solution to obtain a simple linear relation for determining the transmissivity and storage coefficient from recovery data. Unlike other existing straight-line fitting methods, in our method, we applied different approximations to the well functions in the solutions of s1 and s2. We used the well-known Cooper-Jacob approximation for s1, truncating the expansion of the well function in s2 to its first three terms. For the same level of truncation errors, while the Cooper-Jacob approximation requires the argument u1<or=0.01, the second approximation requires the argument u2<or=0.2, thus dramatically improving the utility of short-term recovery data. Application of our method requires only recovery data from a single observation well and no knowledge of the drawdown at the moment of pumping cessation.

Environmental Monitoring↗
PubMedDate not supplied

Hymeniacidon perleve associated bioactive bacterium pseudomonas sp. NJ6-3-1.

Among the marine bacteria isolated from cytotoxic sponge Hymeniacidon perleve, one strain NJ6-3-1 classified as Pseudomonas sp. showed both cytotoxic and antimicrobial activities. Fatty acid analysis indicated that the bacterial strain consists mainly of C16:1, C16:0, C18:1, C18:0, C15:0, C14:0. One unusual 9,10-cyclopropane-C17:0 fatty acid, and C26:0 also constitute as major component as well as the existence of squalene, the precursor of triterpenoids. The major metabolites in the culture broth were identified as alkaloids, including diketopiperazines and indole compounds, namely 3,6-diisopropylpiperazin-2,5-dione, 3-benzyl-3-isopropylpiperazin-2,5-dione, 3,6-bis-(2-methylpropyl)-piperazin-2,5-dione, indole-3-carboxaldehyde, indole-3-caroxylic acid methyl ester, indole-3-ethanol, and quinazoline-2,4-dione.

Animals↗