Biomedical subjects

X F Zhang

Publications and source records attributed to X F Zhang.

At least 73 records · Page 4Linked to original sources

PubMed1994

Substituted phthalocyanine-sensitized photochemical generation of superoxide anion radical.

The quantum yield of phthalocyanine-photosensitized generation of superoxide anion radical (O2-) was measured by the electron spin resonance (ESR) technique. From the redox potential data, it is concluded that O2- is formed by electron transfer from the singlet excited state (not triplet or ground state) of phthalocyanines (PCs) to oxygen. Since a much larger theoretical quantum yield of O2- generation (phi c) than experimental (phi m) was found, it is suggested that charge recombination processes between O2- and PCs+ occur more rapidly than O2- trapping by 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). The results indicate that the use of DMPO as a spin trap is not an ideal method for measurement of the quantity of O2- formed via photosensitization.

Cyclic N-Oxides↗

PubMed1994

Mechanism of photosensitized oxidation of tyrosine by gallium or zinc phthalocyanine in homogeneous and aqueous micellar media.

The mechanism of the photo-oxidation of tyrosine (Tyr) sensitized by sulphonated phthalocyanine at pH 10 in homogeneous aqueous solution or aqueous cetyltrimethylammonium chloride (CTAC) micellar medium was studied by kinetic analysis and laser flash photolysis. Cationic CTAC micelles promote the importance of a type I mechanism in the photo-oxidation of Tyr sensitized by sodium tetrasulphonated chlorogallium phthalocyanine (GaTSPC) whereas they have little effect on the photo-oxidation of Tyr sensitized by sodium disulphonated zinc phthalocyanine (ZnDSPC). In all cases studied, it was shown that the type I mechanism (electron transfer) takes place more easily using GaTSPC as sensitizer, whereas, using ZnDSPC as sensitizer, a type II mechanism (involving 1O2) predominates. The results are discussed according to the mutual position of the sensitizer and the substrate in the aqueous micellar medium and the ability of the triplet state of the phthalocyanine to abstract an electron from Tyr.

Azides↗

PubMed1994

Critical binding and regulatory interactions between Ras and Raf occur through a small, stable N-terminal domain of Raf and specific Ras effector residues.

Genetic and biochemical evidence suggests that the Ras protooncogene product regulates the activation of the Raf kinase pathway, leading to the proposal that Raf is a direct mitogenic effector of activated Ras. Here we report the use of a novel competition assay to measure in vitro the relative affinity of the c-Raf-1 regulatory region for Ras-GTP, Ras-GDP, and 10 oncogenic and effector mutant Ras proteins. c-Raf-1 associates with normal Ras and the oncogenic V12 and L61 forms of Ras with equal affinity. The moderately transforming mutant Ras[E30K31] also bound to the c-Raf-1 regulatory region with normal affinity. Transformation-defective Ras effector mutants Ras[N33], Ras[S35], and Ras[N38] bound poorly. In contrast, the transformation defective Ras[G26I27] and Ras[E45] mutants bound to the c-Raf-1 regulatory region with nearly wild-type affinity. A stable, high-affinity Ras-binding region of c-Raf-1 was mapped to a 99-amino-acid subfragment of the first 257 residues. The smallest Ras-binding region identified consisted of N-terminal residues 51 to 131, although stable expression of the domain and high-affinity binding were improved by the presence of residues 132 to 149. Deletion of the Raf zinc finger region did not reduce Ras-binding affinity, while removal of the first 50 amino acids greatly increased affinity. Phosphorylation of Raf[1-149] by protein kinase A on serine 43 resulted in significant inhibiton of Ras binding. demonstrating that the mechanism of cyclic AMP downregulation results through structural changes occurring exclusively in this small Ras-binding domain.

Cyclic AMP-Dependent Protein Kinases↗

PubMed1994

[A comparative study of therapeutic effects of total versus proximal subtotal gastrectomy in adenocarcinoma of the gastric cardia].

485 patients with adenocarcinoma of the gastric cardia operated in our hospital. 283 cases were treated with total gastrectomy, and 202 cases were treated with proximal subtotal gastrectomy. The age, sex, clinical stage, size of tumour, radicality of surgical resection, lymph node involvement, tumour depth penetration and histological type had no significant difference in the two groups. Analysis of survival rates failed to demonstrate any significant difference between the two types of surgical operation for TNM stage I and II. Total gastrectomy resulted in significantly higher survival rate than proximal subtotal gastrectomy for stage III. The 3- and 5-year survival rate of TNM stage III patients increased by 14.6% and 15.1%, respectively (P < 0.05). Extended total gastrectomy was usually applied for stage IV patients without distant metastasis. If the neoplasm had spread beyond the confines of extended total gastrectomy, in order to eliminate obstruction or bleeding, palliative proximal subtotal gastrectomy or total gastrectomy should be considered.

Adenocarcinoma↗

PubMed1994

Genotypic identification of seven Rickettsia conorii strains.

Restriction endonuclease fragment length polymorphism (RFLP) analysis and polymerase chain reaction (PCR) were used to characterize the genotypic diversity of 7 strains of Rickettsia conorii from South Africa, Ethiopia, Morocco, India and Russia. The strains of R. conorii were divided into four genotypes by Rsa I or Pst I endonuclease digestion of PCR-amplified rickettsial DNA using primers derived from the R. rickettsii 190 K antigen gene. M-1 and Barbash strains were genotypically identical, but different from Indian, Ethiopian and S7 strains, which formed another group. Simko and Moroccan strains were genotypically different from each other and also from other strains of R. conorii. We conclude that there exist a genotypic diversity among intraspecies of R. conorii.

Africa↗

PubMed1994

[Inhibition of mexiletine on sodium current in dorsal root ganglion neurons of rats].

Using whole-cell configuration of patch clamp technique we found that mexiletine (Mex) reversibly inhibited the sodium current in a voltage- and use-dependent manner in cultured dorsal root ganglion (DRG) neurons. The threshold concentration of Mex was 5 mumol.L-1. The inhibitory action heightened with increasing concentrations of Mex. Complete inhibition was achieved at 150 mumol.L-1 and the 50% inhibition concentration was 31 mumol.L-1. It is suggested that the inhibition of Mex on sodium current in neurons may be one of the mechanisms of its anti-ischemic and anti-anoxic effects on the neuron.

Animals↗

PubMed1994

[Differential reactivities of three kinds of carbon dioxide absorbents with sevoflurane].

The differential reactivities of three kinds of carbon dioxide absorbents, Soda lime, Soda lime A, and Baralyme with sevoflurane were investigated. Sevoflurane was made to react with each carbon dioxide absorbents in a glass vial or in a closed system under administration of carbon dioxide. Glass vials were kept at 55 degrees C and 70 degrees C, and three kinds of carbon dioxide absorbents were compared regarding their reactivity under each temperature. In a closed system, we also monitored the temperature of glass container which was filled with each carbon dioxide absorbent. In a glass vial, the highest reactivity of sevoflurane was found with Baralyme. Although Soda lime A decomposed sevoflurane less than Baralyme or Soda lime in glass vial, the highest reactivity of sevoflurane in a closed system was found with Soda lime A. On the other hand, Soda lime A increased the temperature of glass container most. As increasing temperature tends to promote reaction, the possibility that the high temperature of the glass container contributes to the reactivity of sevoflurane with carbon dioxide absorbents exists. These results suggest that the highest reactivity of Soda lime A with sevoflurane was caused by the highest temperature of glass container although its chemical composition makes it most reactive with sevoflurane than the others.

Calcium Compounds↗

PubMed1993

Normal and oncogenic p21ras proteins bind to the amino-terminal regulatory domain of c-Raf-1.

In higher eukaryotes, the Ras and Raf-1 proto-oncoproteins transduce growth and differentiation signals initiated by tyrosine kinases. The Ras polypeptide and the amino-terminal regulatory domain of Raf-1 (residues 1-257) are shown to interact, directly in vitro and in a yeast expression system. Raf-1 (1-257) binds GTP-Ras in preference to GDP-Ras, and inhibits Ras-GAP activity. Mutations in and around the Ras effector domain impair Ras binding to Raf-1 (1-257) and Ras transforming activity in parallel.

Animals↗

PubMed1993

Expression and phosphorylation of insulin receptor substrate 1 during rat liver regeneration.

Insulin has been shown to be important for normal liver regeneration to occur. The mechanisms whereby insulin may exert its effects on hepatocyte growth, however, are still unknown. The rat and human insulin receptor substrate 1 (IRS-1) is a specific target molecule for the insulin receptor beta subunit kinase and will bind to signal transducing molecules containing Src homology 2 domains through its multiple tyrosyl phosphorylation (TP) sites. This investigation examined how IRS-1 may be involved in insulin action during hepatocyte growth induced by two-thirds partial hepatectomy. The TP of IRS-1 was strikingly enhanced prior to the major wave of hepatocyte DNA synthesis at 24 h; IRS-1 protein and mRNA expression increased in parallel to a lesser extent after partial hepatectomy. TP of insulin receptor beta subunit, which enhances its kinase activity toward IRS-1, was increased in association with TP of IRS-1. Finally, phosphatidylinositol 3-kinase, one of signal transducing molecules containing Src homology 2 domains, was associated with IRS-1 following TP in vivo. These observations suggest that IRS-1 protein may play an important role in transmitting the insulin signal to intracellular regulators involved in hepatocyte growth.

Animals↗

PubMed1993

[Indirect testimony of stress conduction from mandible to skull in maxillofacial trauma: morphological changes of temporomandibular joint disc]

There were cerebral injuries accompanied in maxillofacial high velocity projectile wound.Owing to the special anatomic relationship between skull and facial bones,the stress conduction of bone was an important factor of cerebral injury in maxillofacial wound.In this experiment,the canine mandibular regions were wounded by steel spheres,which weight 1.03g,impacting velocity at 1400m/s,to produce severely maxillofacial firearm wounds.The morphological and pathological changes of temporomandibular joint disc of wounded side were observed with light and electron microscopes.The microscopic injuries of disc,including arrangement disorder of figre,spotty edema and some fibrous dissolution,etc,were found.These results have provided an indirect evidence of injurous mechanism of the cerebral injury accompaning maxillofacial high enery misslle wound.

Journal Article↗

PubMed1993

[Preliminary study on hemodynamics in post hepatitic cirrhotic patients with portal hypertension (PCPH) using Doppler ultrasound].

Hemodynamics was studied in normal volunteers and pre- and postoperative patients with PCPH using Doppler ultrasound. There was a systemic hyperdynamic circulatory state in patients with PCPH derived mainly from hyperdynamic splenic circulatory state. Congestion index (CI) of portal vein greater than 0.1cm. s, splenic vein cross section area greater than 0.6cm2, and SVF/PVF greater than 50%, all of these are the hemodynamic diagnostic criterion of PCPH. Both portasystemic shunt and porta-azygous devascularization lowered the hyperdynamic circulatory state of PCPH.

Female↗

PubMed1992

Raf-1 activates MAP kinase-kinase.

The normal cellular homologue of the acutely transforming oncogene v-raf is c-raf-1, which encodes a serine/threonine protein kinase that is activated by many extracellular stimuli. The physiological substrates of the protein c-Raf-1 are unknown. The mitogen-activated protein (MAP) kinases Erk1 and 2 are also activated by mitogens through phosphorylation of Erk tyrosine and threonine residues catalysed by a protein kinase of relative molecular mass 50,000, MAP kinase-kinase (MAPK-K). Here we report that MAPK-K as well as Erk1 and 2 are constitutively active in v-raf-transformed cells. MAPK-K partially purified from v-raf-transformed cells or from mitogen-treated cells can be deactivated by phosphatase 2A. c-Raf-1 purified after mitogen stimulation can reactivate the phosphatase 2A-inactivated MAPK-K over 30-fold in vitro. c-Raf-1 reactivation of MAPK-K coincides with the selective phosphorylation at serine/threonine residues of a polypeptide with M(r) 50,000 which coelutes precisely on cation-exchange chromatography with the MAPK-K activatable by c-Raf-1. These results indicate that c-Raf-1 is an immediate upstream activator of MAPK-K in vivo. To our knowledge, MAPK-K is the first physiological substrate of the c-raf-1 protooncogene product to be identified.

3T3 Cells↗

PubMed1992

[Establishment and computer drawings of a dynamic mathematical eyeball model].

A dynamic mathematic model of the eyeball is established with the computer on the basis of ocular anatomical data and equations of the axial length as the variable in relation to other parameters. With an automatic plotter, the model is transformed into 4 geometric diagrams of the frontal and lateral views, and the meridian and coronary sections. Meanwhile, a set of pictures for intraocular foreign body localization is developed.

Computer Graphics↗

PubMed1991

Image analysis-based measurement of DNA supercoiling changes in transformed and nontransformed human cell lines.

An image analysis system was used to visualize and measure the changes in nucleoid diameter (nuclear matrix core plus extruded DNA loops) which occur when increasing concentrations of propidium iodide are used to titrate the DNA supercoiling response. Parallel core size measurements allow estimates of the changes in apparent DNA loop size. Unlike sedimentation assays, DNA loop size estimates are not influenced by particle mass, require no prior cell labeling, and can be performed on a per cell basis. This technique was used to examine changes in DNA loop characteristics which may occur when cells are transformed or undergo changes in their proliferative state. SV40-transformation of human diploid fibroblast lines resulted in a significant increase in both the nucleoid core and average DNA loop size. Lymphoblast cell lines also had larger nucleoid dimensions than normal lymphocytes. The response of several established human tumor cell lines indicated slightly increased loop but not core sizes as compared to normal human diploid fibroblasts. Changes in proliferative state also resulted in changes in DNA loop characteristics as measured in this assay. Both quiescent fibroblasts and unstimulated lymphocytes appeared to have smaller or more condensed DNA loop structures than their proliferating counterparts. These results demonstrate the utility of this assay in detecting changes in DNA loop structure which occur in association with changes in the proliferative activity of cells in culture.

Cell Cycle↗

PubMed1991

[Effects of fasting and infusion of acid-base balance, electrolyte and plasma glucose level in children during operation].

We studied the effects of fasting and infusion different fluid on acid-base balance, electrolyte and plasma glucose level in 50 children during operation. After whole night fasting, 26 of 44 children (59.1%) were found to have metabolic acidosis, and 5 of 42 children (11.9%) have hypokalemia. The serum K+ level of 30 of 42 children (71.4%) and the serum Na+ level of 6 of 48 children (12.5%) were lower than normal. The serum Cl- level of 21 of 48 children (43.8%) was higher than normal. The serum glucose level of 6 of 48 children was lower than normal. One of 48 children (2.1%) had hypoglycemia. The effects of infusing deferent fluids on acid-base balance, electrolytes and plasma glucose level were compared. The results showed that in patients infusing 10% dextrose with Ringer's solution or 5% Dextrose with normal saline, the plasma glucose level, electrolytes maintained at the normal level or acidosis corrected significantly. It is suggested that 10% dextrose with Ringer's solution and 5% dextrose with normal saline are infused during operation for children.

Acid-Base Equilibrium↗

PubMed1990

[Epidemiological survey of epidemic haemorrhagic fever in Xianning County].

The incidence, distribution pattern and trend of disease spreading of EHF in Xianning Country, Hubei province during 1971-1985 are described. Serologic study showed that the serum antigen positivity rate was 12.90% for Apodemus Agragrius and 6.67% for Rattus Norvegicus and that the serum antibody positivity rate was 61.54% in FHF patients and 30.85% in the exposed contacts of the patients' families in the epidemic area. In 1985, the HFRS virus A24 was isolated from Apodemus Agragrius and identified.

Adolescent↗

PubMed1990

[Clinical experience in the treatment of 1108 patients with gastric carcinoma].

From June 1972 to December 1986, 1108 patients with gastric cancer were treated in our hospital. Of them, 113 received non-operative therapy, 995 were operated and 803 had resectable tumors with a resection rate of 80.4%. 1042 patients were followed with a follow-up rate of 94.0%. The 1, 3 and 5 year survival rates were 81.4% (638/783), 42.3% (280/662) and 30.0% (159/529), respectively. According to our data, R2 or selective R3 procedure may be used as standard for advanced gastric carcinoma. For the stage IV patients whose tumors were not radically resected, palliative gastrectomy should be undertaken, if possible. Postoperative adjuvant chemotherapy can improve survival rates in patients with stages III and IV lesions.

Adult↗

PubMed1989

Further study on the role of Mg2+ in lipid-protein interaction in reconstituted porcine heart mitochondrial H+-ATPase.

Porcine heart mitochondrial H+-ATPase was reconstituted by cholate dialysis method in liposomes containing neutral (PC, PE), acidic (PG, PI, PA, PS, DPG) or neutral and acidic phospholipids. The Mg2+ effect on the ATPase activity and its sensitivity to oligomycin, ATP-induced delta psi and delta pH formation was observed for the proteoliposomes containing acidic but not neutral phospholipids. Maleimide spin labels with varying arm lengths or bromoacetamide spin probe were used to monitor the conformational difference of H+-ATPase in the Mg2+-containing and Mg2+-'free' samples. A difference in W/S ratio (weakly immobilized/strongly immobilized component in the ESR spectra) could be detected for the F0.F1-containing and F1-depleted, (F0)-containing proteoliposomes, suggesting conformational difference in the F0-F1 complex and F0 portion induced by the Mg2+ effect. A conformational change of the beta-subunits in the F1 portion was also deduced from the ATP-induced fluorescence quenching of aurovertin-complex for Mg2+-containing samples. The results obtained are in favor of our previous assumption that Mg2+ may play its role by altering the physical state of the lipid bilayer, which would induce a conformational change in F0 (buried in the lipid core), which in turn is transmitted to the catalytic F1, resulting in a higher enzyme activity.

Adenosine Triphosphate↗