Search PubMed⌕ Search

Biomedical subjects

L Ma

Publications and source records attributed to L Ma.

At least 469 records · Page 26Linked to original sources
PubMed1995

Proton nuclear magnetic resonance studies on huwentoxin-I from the venom of the spider Selenocosmia huwena: 1. Sequence-specific 1H-NMR assignments.

The complete sequence-specific assignments of resonances in the 1H-NMR spectrum of huwentoxin-I from the Chinese bird spider, Selencocosmia huwena, is described. A combination of two-dimensional NMR experiments including 2D-COSY, 2D-NOESY, and 2D-TOCSY has been employed on samples of the toxin dissolved in D2O and in H2O for assignment purposes. Protons belonging to spin systems for each of the 33 amino acids were identified. The sequence-specific assignments were facilitated by the identification of d alpha N connectivities on the fingerprint regions of the COSY and NOESY spectra and were supported by the identification of dNN and d alpha N connectivities in the TOCSY and NOESY spectra. These studies provide a basis for the determination of the solution-phase conformation of this toxin.

Amino Acid Sequence↗
PubMed1995

Expression of p53 in oesophageal squamous cell carcinoma in Hong Kong Chinese.

We studied p53 overexpression in a series of 99 primary oesophageal squamous cell carcinomas (28 well-differentiated, 42 moderately-differentiated and 29 poorly-differentiated squamous cell carcinomas) from Chinese patients using the p53 protein specific mouse monoclonal antibody DO-7 on paraffin sections. The p53 protein was detected in 30% (30 cases) of the tumours. A significantly higher positive rate was noted in the poorly-differentiated tumours (11% for the well-differentiated, 31% for the moderately-differentiated and 48% for the poorly-differentiated tumours). In addition, strong positive p53 staining was identified only in the less differentiated tumour cells in the periphery of the tumour cell nests in all the cases and the expression was weaker in the better differentiated foci. The central keratinizing areas and the immediately adjacent tumour cells were always negative for p53. The adjacent normal oesophageal mucosa was all negative for p53 protein but the non-invasive dysplastic epithelium next to the tumours could also be strongly positive for p53 protein (four out of 14 cases in which the dysplastic epithelium adjacent to the tumour was adequately sampled). In two out of these four cases, the dysplastic epithelium showed staining for p53; even the adjacent invasive tumour was negative for p53. It is concluded that there is a strong relationship between p53 overexpression and tumour cell differentiation in oesophageal squamous carcinoma and overexpression of p53 can occur in non-invasive tumour cells.

Aged↗
PubMed1995

Absence of Epstein-Barr virus in oesophageal squamous cell carcinoma.

Aim-To identify the possible role of Epstein-Barr virus (EBV), in Chinese patients, in the pathogenesis of oesophageal squamous cell carcinoma.Methods-Formalin fixed, paraffin wax embedded tissues from 74 cases of oesophageal squamous cell carcinoma (28 with well differentiated, 27 with moderately differentiated and 18 with poorly differentiated carcinomas) were analysed for EBV using in situ hybridisation for EBV encoded small RNAs.Results-EBV was detected in only a few lymphocytes adjacent to the tumour epithelia in 14 (19%) cases of oesophageal carcinoma. The adjacent, non-pathological oesophageal tissue was EBV negative.Conclusions-EBV does not play a major role in the aetiology of oesophageal squamous cell carcinoma.

Journal Article↗
PubMed1995

Genetic linkage of thymic T-cell proliferative unresponsiveness to mouse chromosome 11 in NOD mice. A possible role for chemokine genes.

Thymic and peripheral T-cells from NOD mice display a proliferative unresponsiveness on stimulation through the T-cell receptor/CD3 complex. Interleukin 4 reverses NOD T-cell unresponsiveness in vitro and prevents the onset of diabetes in vivo, suggesting a causal relationship between the T-cell unresponsiveness and diabetes susceptibility in NOD mice. Both quantitative trait loci analysis of BXD recombinant inbred mice and linkage analysis of NOD outcross populations reveal that the control of NOD thymic T-cell proliferative unresponsiveness genetically maps to a central region on mouse chromosome 11, which includes the beta-chemokine gene family. This finding raises the possibility that a beta-chemokine(s) may regulate T-cell unresponsiveness as well as diabetes susceptibility in NOD mice.

Animals↗
PubMed1995

[Study on effect of polysaccharides of ginseng on peripheral blood mononuclear cell induced interleukin-2 production and activity of its receptors in vitro].

To study the effect of polysaccharides of Ginseng (PSG) on cellular-immunity from healthy subjects and patients of kidney disease, the peripheral blood mononuclear cell (PBMC) induced interleukin-2 (IL-2) were assayed in vitro. It was found that the PSG could prommote the PBMC induced IL-2 in the healthy subjects and patients with kidney diseases and was dose-dependent. This study revealed that PSG was worthwhile to be further studied as an approach of biological responsive modifier therepy in treating human immunodeficiency diseases.

Adolescent↗
PubMed1995

Combined treatment of ionizing radiation and photosensitization by 5-aminolevulinic acid-induced protoporphyrin IX.

The response of human colon adenocarcinoma cells of the line WiDr to the combined treatment of ionizing radiation and photosensitization by 5-aminolevulinic acid-induced protoporphyrin IX was assessed by a colony-forming assay. A dose of X rays inactivating approximately 50% of the cells was used. Seventy to 85% of the cells accumulated in S and G2 + M phase 12-24 h after such a treatment as measured by flow cytometry, while the distribution of cells in the phases of the cell cycle approached that of untreated cells 48 h after X-ray treatment. Cellular photosensitization was developed by endogenous synthesis of protoporphyrin IX (PPIX) from the precursor 5-aminolevulinic acid (5-ALA). This was performed by treating the cells with 1 mM 5-ALA for 4 h in a serum-free medium. The endogenous synthesis of PPIX increased with time after the cells had been subcultured, i.e. the ability of the cells to synthesize PPIX increased 1.5-2-fold within 48 h of incubation. This was not due to effects of trypsin on the cells. Photochemotherapy with 5-ALA was given 0-48 h after X rays. The combined cytotoxic effect was analyzed by an isobologram after correction of the survival curves for microcolony formation and differences in intracellular concentration of PPIX. The results indicate that 5-ALA PCT given 0-4 h after X rays acts slightly antagonistically while 5-ALA PCT given 12-48 h after X rays acts slightly synergistically.

Adenocarcinoma↗
PubMed1995

[In situ expression of intercellular adhesion molecule-1 in human glomerulonephritis].

We conducted immunocytochemical analysis with in situ hybridization technique to investigate the presence and role of intercellular adhesion molecule-1 (ICAM-1) in normal and diseased kidneys. A total of 64 renal biopsy specimens were classified in three groups according to the degree of cellular proliferation in glomerulus. Group A presented no or mild proliferation (n = 38). Group B showed definite proliferation (n = 21). Group C had glomerular sclerosis (n = 5). The ratio of cases exhibiting increased glomerular ICAM-1 expression in lupus nephritis (9/10) was significantly different from that in minimally changed disease (1/5) (P = 0.017). Glomerular ICAM-1 expression level correlated well with the cellular proliferation and infiltration in glomerulus (B&A: P < 0.001; C&B: P < 0.05). The percentage of cases with tubular ICAM-1 positivity in group B (81.0%) and group C (100%) was greater than that in group A (52.6%), which was also correlated with that of interstitial cell infiltration. In situ hybridization of 9 renal biopsies with digoxigenin labelled oligo probe proved immunocytochemical findings. We conclude that glomerular ICAM-1 expression level is correlated with inflammatory degree of glomerulus and that tubular ICAM-1 expression is associated with interstitial cell infiltration.

Gene Expression↗
PubMed1995

[A study on the relationship between drinking water with high arsenic content and incidence of malignant tumour in Heihe Village, western part of Huhehot, Inner Mongolia].

Since 1991, it has been repeatedly reported that endemic arsenism was noticed in the large areas in the middle and west parts of Inne Mongolian Autonomous Region. Heihe village is located in a geological area with rich natural arsenic. The inhabitants of the village have drunk the water with high arsenic content for a long time and many people have died of malignant tumours. A historical prospective method has been used in the study. The research has been carried out chronologically on the statistical relationship between drinking water with high arsenic content consumed by local inhabitants for 22 years and the mortality of malignant tumours. This study has confirmed that the accumulated mortality rate and the average mortality rate of Heihe villagers who had drunk the water with high arsenic content for a number of total 22 years (from January 1971 to January 1993) were 13 590/10(5) person-year and 642.01/10(5) person-year. In terms of the portion among all malignant tumour deaths, cancer for the lung takes the lead, followed by liver cancer and then bladder cancer. The risk of death of malignant tumours in the villagers who drink water with high arsenic content was 9.38 times to the risk in the inhabitants who do not drink water with high arsenic content.

Arsenic↗
PubMed1994

Mutations at histidine 412 alter zinc binding and eliminate transferase activity in Escherichia coli alkaline phosphatase.

His-412 in wild-type Escherichia coli alkaline phosphatase is a direct ligand to one of the two zinc atoms critical for the function of the enzyme. To investigate the function of this residue, site-specific mutagenesis was used to substitute His-412 with asparagine and alanine, generating mutant enzymes H412N and H412A, respectively. Both mutant enzymes show a 5-fold decrease in kcat and 30-fold increase in Km when compared to the corresponding kinetic parameters for the wild-type enzyme. In contrast to the wild-type enzyme, Tris and ethanolamine inhibit both the mutant enzymes by inhibiting the hydrolysis reaction and not participating in the transferase reaction; furthermore, both mutants have lower zinc and phosphate content than the wild-type enzyme. The addition of Zn2+ to the H412N and H412A enzymes restores catalytic activity to within 2-fold of the value for the wild-type enzyme, but more importantly the presence of Zn2+ completely restores substrate affinity. The similarity in the kinetic parameters for the H412N and H412A enzymes in the absence and presence of zinc suggests that the asparagine side chain does not play a significant role in coordinating zinc. Furthermore, both the asparagine and alanine substitutions reduce the affinity of the resulting enzymes for zinc. The pH profiles for the two mutant enzymes are different than the pH profile observed for the wild-type enzyme, suggesting that the amino acid substitutions may have altered the pKa of the zinc coordinated water molecule that is critical in the second step of the mechanism. These data suggest that His-412 does not directly participate in the catalytic mechanism but is mainly involved in zinc binding, and therefore is also indirectly involved in substrate binding and product release.

Alkaline Phosphatase↗
PubMed1994

A sialoglycoprotein from human leukocytes functions as a ligand for P-selectin.

P-selectin (CD62P), a Ca(2+)-dependent lectin expressed on activated platelets and endothelial cells, functions as a receptor for myeloid and monocytoid cells. Previous reports have described a homodimeric sialoglycoprotein from human leukocytes and HL-60 cells specifically recognized by P-selectin. We describe here a panel of monoclonal antibodies prepared against high molecular weight fractions of HL-60 cell membranes. These antibodies are of IgM isotype, bind to a approximately 240-kDa protein from human leukocyte membranes which is also reactive with P-selectin. They recognize a Ca(2+)-dependent, sialidase-sensitive determinant on myeloid and monocytoid cell lines. Each antibody specifically inhibits adhesion of neutrophils or HL-60 cells to: 1) purified P-selectin, 2) thrombin-stimulated platelets, and 3) phorbol 12-myristate 13-acetate-activated endothelial cells. These results suggest that the sialoglycoprotein recognized by this panel of monoclonal antibodies may function as a cell surface ligand for P-selectin.

Amino Acid Sequence↗
PubMed1994

The xeroderma pigmentosum group B protein ERCC3 produced in the baculovirus system exhibits DNA helicase activity.

The XPB/ERCC3 gene corrects the nucleotide excision-repair defect in the human hereditary disease xeroderma pigmentosum group B and encodes the largest subunit of the basal transcription factor BTF2/TFIIH. The primary sequence of the XPB/ERCC3 protein features the hallmarks of seven helicase motifs found in many known and putative helicases or helicase-related proteins. Recently, the multiprotein BTF2/TFIIH complex has been found to be associated with DNA helicase activity. To explore the properties and functions of XPB/ERCC3, we have used the baculovirus/insect-cell expression system to produce recombinant protein. We report here the construction and analysis of recombinant baculovirus expressing XPB/ERCC3. The XPB/ERCC3 protein is synthesized at a relatively high level in baculovirus-infected insect cells. While the majority of XPB/ERCC3 end up in the insoluble fraction of insect cell lysates, a minor fraction of recombinant protein is present in soluble form which can be purified under native conditions. We have found that a DNA helicase activity is associated with the purified XPB/ERCC3 protein, suggesting that XPB/ERCC3 may function as a DNA helicase in local unwinding of DNA template both in the context of transcription and nucleotide excision repair.

Amino Acid Sequence↗
PubMed1994

Purification and characterization of a FeMo cofactor-deficient MoFe protein.

Previous studies have shown that the nifH gene product is required for FeMo cofactor biosynthesis and insertion and that a delta nifH strain of Azotobacter vinelandii designated DJ54 accumulates a FeMo cofactor-deficient MoFe protein that is distinct from the FeMo cofactor-deficient protein synthesis by Nif B-, N-, or E- strains [Tal, S., Chun, T., Gavini, N., & Burgess, B. K. (1991) J. Biol. Chem. 266, 10654-10657]. Here we report the purification and activation of the MoFe protein from DJ54. The purified protein is an alpha 2 beta 2 tetramer that is indistinguishable from the wild-type MoFe protein by the criteria of SDS-polyacrylamide gel electrophoresis, native gel electrophoresis, and two-dimensional gel electrophoresis. It binds normally to its redox partner, the Fe protein, by the criterion of chemical cross-linking. It does not contain FeMo cofactor and does not catalyze significant C2H2 reduction or reduction-independent MgATP hydrolysis. It can, however, be activated with FeMo cofactor following the addition of the Fe protein and MgATP when an additional required component(s) is supplied by cell-free extracts from a delta nifD strain of A. vinelandii. The purified DJ54 MoFe protein does contain P-clusters by the criteria of metal analysis, CD spectroscopy, cluster extrusion, and electrochemical reduction of the POX state. In the presence of dithionite it exhibits an axial S = 1/2 EPR signal that integrates to 0.1-0.3 spin per alpha 2 beta 2 tetramer.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗