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Biomedical subjects

L Wei

Publications and source records attributed to L Wei.

At least 271 records · Page 15Linked to original sources
PubMed1991

The two homologous domains of human angiotensin I-converting enzyme are both catalytically active.

Molecular cloning of human endothelial angiotensin I-converting enzyme (kininase II; EC 3.4.15.1) (ACE) has recently shown that the enzyme contains two large homologous domains (called here the N and C domains), each bearing a putative active site, identified by sequence comparisons with the active sites of other zinc metallopeptidases. However, the previous experiments with zinc or competitive ACE inhibitors suggested a single active site in ACE. To establish whether both domains of ACE are enzymatically active, a series of ACE mutants, each containing only one intact domain, were constructed by deletion or point mutations of putative critical residues of the other domain, and expressed in heterologous Chinese hamster ovary cells. Both domains are enzymatically active and cleave the C-terminal dipeptide of hippuryl-His-Leu or angiotensin I. Moreover, both domains have an absolute zinc requirement for activity, are activated by chloride and are sensitive to competitive ACE inhibitors, and appear to function independently. However, the two domains display different catalytic constants and different patterns of chloride activation. At high chloride concentrations, the C domain hydrolyzes the two substrates tested faster than does the N domain. His-361,365 and His-959,963 are established as essential residues in the N and C domains, respectively, most likely involved in zinc binding, and Glu-362 in the N domain and Glu-960 in the C domain are essential catalytic residues. These observations provide strong evidence that ACE possesses two independent catalytic domains and suggest that they may have different functions.

Amino Acid Sequence↗
PubMed1991

Expression and characterization of recombinant human angiotensin I-converting enzyme. Evidence for a C-terminal transmembrane anchor and for a proteolytic processing of the secreted recombinant and plasma enzymes.

Chinese hamster ovary (CHO) cells have been transfected with either a full-length cDNA encoding human angiotensin I-converting enzyme (kininase II; EC 3.4.15.1) (ACE) or a mutated cDNA, in which the last C-terminal 47 amino acids, including the putative transmembrane domain, are not translated. Cell lines expressing high levels of the wild-type ACE or the mutant were established. The cells transfected with the wild-type cDNA (CHO-ACE) express a membrane-bound ectoenzyme with an intracellular C terminus, as shown by indirect immunofluorescence using an antiserum (28A7) raised against a synthetic peptide corresponding to the deduced C terminus of ACE. This enzyme is structurally, immunologically, and enzymatically identical to human kidney ACE. In addition, CHO-ACE cells also produce a secreted form of the enzyme. Neither this secreted form nor the enzyme purified from human plasma is recognized by the antiserum 28A7, indicating that they undergo a truncation in the C-terminal region. On the other hand, the transfected cells expressing the C-terminally truncated mutant (CHO-ACE delta COOH) do not retain ACE in the plasma membrane, but secrete it into the medium. These results indicate that ACE is anchored to the plasma membrane by the predicted C-terminal transmembrane domain, and the secreted form is derived from the membrane-bound form by a post-translational proteolytic cleavage of the C-terminal region.

Amino Acid Sequence↗
PubMed1991

Functional variations in parenchymal microvascular systems within the brain.

Variations in microvascular system functions were observed among a number of brain areas. The rates of local blood flow varied 18-fold among areas and were extremely high in neuroendocrine structures. Marked differences in blood flow were also found within some brain structures. The volume of radiolabeled blood in perfused parenchymal microvessels ranged from 5 to 70 microliters/g and correlated closely with local cerebral blood flow. The hematocrits within parenchymal microvessels were 45-75% of the arterial hematocrit, which indicates that red cells more rapidly traverse brain microvessels than do plasma proteins. The mean transit times of blood through parenchymal microvessels were extremely short and ranged from 0.3 to 0.6 s.

Animals↗
PubMed1991

Variation in local cerebral blood flow response to high-dose pentobarbital sodium in the rat.

Microvascular bed structure and functions are known to vary throughout the brain. Microvascular responses to high doses of pentobarbital sodium might therefore differ among brain areas. This possibility was examined by measuring local cerebral blood flow (LCBF) with [14C]iodoantipyrine in 52 brain areas at 5, 10, 25, and 60 min after intraperitoneal administration of pentobarbital (50 mg/kg). From 5 to 60 min, LCBF was significantly lowered in 17 of 25 forebrain gray matter areas but in only 1 of 18 hindbrain gray matter structures, the pontine nuclei. Smaller, shorter duration lowering of LCBF was also observed in ten other brain areas. In both control and treated rats, LCBF was found to vary within individual brain structures. The pattern of these LCBF variations was columnar in the cerebral cortex and the hippocampus but was patchy in the caudate-putamen, thalamus, and inferior colliculus. These results indicate that pentobarbital anesthesia more strongly alters LCBF in the forebrain than in the hindbrain and produces different patterns of changes in LCBF than in local cerebral glucose utilization, which was measured with 2-deoxyglucose in a companion study.

Animals↗
PubMed1991

Pentobarbital produces dissimilar changes in glucose influx and utilization in brain.

The effects of pentobarbital sodium on local cerebral glucose utilization (LCGU) and 3-O-methylglucose (3-MG) influx were measured by quantitative autoradiography in 52 brain areas of control and treated rats. Pentobarbital (50 mg/kg ip) lowered LCGU to a relatively uniform rate (approximately 35 mumol.100 g-1.min-1) in 24 of 25 forebrain areas. Among the 18 hindbrain areas, LCGU was decreased by pentobarbital by 15-55% (range 50-157 and 28-110 mumol.100 g-1.min-1 in control and treated rats, respectively). In contrast, pentobarbital lowered the 3-MG influx rate constant and permeability-surface area product by 20-30% in nearly all brain structures. The 3-MG results fit a model in which both the half-saturation constant and the maximal velocity of the glucose carrier are decreased by pentobarbital. After pentobarbital treatment, the ratio of local cerebral plasma flow (LCPF) to LCGU was the same as in controls for brain areas in which LCGU was less than 35 mumol.100 g-1.min-1 but was higher in brain areas where LCGU exceeded 35 mumol.100 g-1.min-1. Pentobarbital produced dissimilar changes in LCGU, 3-MG influx, and LCPF; these processes may thus not be closely linked during pentobarbital anesthesia.

3-O-Methylglucose↗
PubMed1991

[Cloning and sequencing of spinach chloroplast DNA fragments with promoter activities in E. coli].

Sau3A partially digested spinach cDNA fragments were cloned in BgIII restriction site of a E. coli promoter probing vector pGA46. The cloned fragments with promoter activities in E. coli were found by the abilities of recovering tetracycling resistance of their host cells. The promoter functions of the two fragments and their different strengths are deciphered by analyzing their DNA sequences.

Base Sequence↗
PubMed1991

[Analysis of volatile oil in pericarpium Zanthoxyli].

Essential oils were extracted from the pericarp of Zanthoxylum bungeanum and Z. schinifolium. The chemical constituents were analysed by means of GC-MS and 33 compounds were identified. Their contents in the essential oil were also determined.

Acyclic Monoterpenes↗
PubMed1991

Chromosome aberration, cancer mortality and hormetic phenomena among inhabitants in areas of high background radiation in China.

The respective average annual doses are about 330 and 110 mR/yr, in the high background radiation areas (HBRA) in Yangjiang County and the control areas (CA) in Enping and Taishan Counties. Both the HBRA and CA are in Guangdong Province which borders the South China Sea. The frequencies of chromosome aberration in circulating lymphocytes were examined for persons residing in the HBRA and CA. Those in the HBRA had increased frequencies of detectable abnormalities in stable aberrations (translocations and inversions) and unstable aberrations (dicentrics and rings). Previous reports have shown that when samples of circulating lymphocytes taken from inhabitants were tested in vitro for mitotic responses to phytohemagglutinin (PHA) and for the degree of unscheduled DNA synthesis (UDS) induced by UV-irradiation, there were higher responsiveness and UDS rates for those in the HBRA than in the CA. In contrast, mortality from all cancers and those from leukemia, breast and lung cancers that are inducible by radiation was not higher in the HBRA. Although the differences in the cancer mortality rates for the HBRA and CA are not significant, the findings are compatible with the assumption that the lower mortality from cancer in the HBRA is the result of the hormetic effects of the three-fold higher dose rate of background radiation in that areas. This assumption requires further study.

Adolescent↗
PubMed1989

18-substituted steroids--Part 17. 2 alpha-hydroxylated liver metabolites of aldosterone identified by high-field [1H]NMR spectroscopy.

11 beta,18-Epoxy-2 alpha,3 alpha,18,21-tetrahydroxy-5 alpha,17 alpha- pregnan-20-one (2 alpha-hydroxy-3 alpha,5 alpha-tetrahydro-17-isoaldosterone) and its apo isomer have been identified by high-field NMR studies, supported by thermospray HPLC/MS, to be among the major polar metabolites formed from incubation of aldosterone with rat liver microsomal fraction. Indications that unreduced 2 alpha-hydroxy-aldosterone is also present among the metabolites have still to be confirmed.

Aldosterone↗
PubMed1989

Regulation of angiotensinogen gene.

The development of recombinant DNA technology has introduced new directions for the study of the angiotensinogen molecule. The cloning and sequencing of the human and rat cDNAs demonstrate the similarity of angiotensinogen to various serine protease inhibitors produced by the liver and was the beginning of studies looking for new physiological roles of angiotensinogen, in addition to the substrate for renin. The determination of the nucleotide sequence of these cDNAs also allowed the identification of angiotensinogen mRNA in many tissues in addition to the liver that is the major site of synthesis. This multilocalization of angiotensinogen is one of the arguments for the presence and the function of local renin-angiotensin systems. Finally, the hepatic biosynthesis of angiotensinogen is regulated by many different hormonal factors including glucocorticoid, estrogen, thyroid hormone, insulin, and angiotensin II. The cloning of the angiotensinogen gene offers the opportunity to study this regulation at the transcriptional level. We present in this paper a review of the literature concerning the new aspects of angiotensinogen using molecular biological tools and its regulation together with the characterization of the human angiotensinogen gene.

Amino Acid Sequence↗
PubMed1988

Expression and characterization of recombinant human angiotensinogen in a heterologous eukaryotic cell line.

Transfection of Chinese hamster ovary cells with an expression plasmid containing a full length human angiotensinogen cDNA has provided cell lines that secrete recombinant angiotensinogen in large quantities. This angiotensinogen is immunologically identical to plasma angiotensinogen and can be cleaved by human kidney renin (EC 3.4.23.15.). The peptide liberated by renin cleavage is immunologically identical to standard angiotensin I and shows a retention time on isocratic reversed-phase high-pressure liquid chromatography identical to that of standard angiotensin I. The heterogeneity of recombinant angiotensinogen on sodium dodecyl sulfate-polyacrylamide gel electrophoresis differs from that of plasma angiotensinogen. Treatment with endoglycosidases demonstrated that this difference is restricted to that of N-glycans and that N-glycans correspond to the quasi-totality of the carbohydrate content of both recombinant and plasma angiotensinogens. The development of a system capable of expressing human angiotensinogen cDNA in mammalian cells and the ability to obtain the corresponding angiotensinogen in large quantities will allow new studies on structure-function relationships of this protein.

Angiotensinogen↗
PubMed1985

Diphtheria toxin resistance in human lymphocytes and lymphoblasts in the in vivo somatic cell mutation test.

It has been shown that circulating peripheral blood lymphocytes can be used for the enumeration of 6-thioguanine-resistant cells that presumably arise by mutation in vivo. This somatic cell mutation test has been studied in lymphocytes from human populations exposed to known mutagens and/or carcinogens. The sensitivity of the test could be further enhanced by including other gene markers, since there is evidence for locus-specific differences in response to mutagens. Resistance to diphtheria toxin (Dipr) seemed like a potential marker to incorporate into the test because the mutation acts codominantly, can readily be selected in human diploid fibroblasts and Chinese hamster cells with no evidence for cell density or cross-feeding effects, and can be assayed for in nondividing cells by measuring protein synthesis inhibition. Blood samples were collected from seven individuals, and fresh, cryopreserved, or Epstein-Barr virus (EBV)-transformed lymphocytes were tested for continued DNA synthesis (3H-thymidine, autoradiography) or protein synthesis (35S-methionine, scintillation counting). Both fresh and cryopreserved lymphocytes, stimulated to divide with phytohemagglutinin (PHA), continued to synthesize DNA in the presence of high doses of diphtheria toxin (DT). Similarly, both dividing (PHA-stimulated) and nondividing fresh lymphocytes carried on significant levels of protein synthesis even 68 hr after exposure to 100 flocculating units (LF)/ml DT. The findings were confirmed in cord blood lymphocytes, ruling out the possibility that diphtheria immunization could have led to a selection of Dipr lymphocytes. One lymphoblast line (EBV-transformed lymphocytes) showed a reduction in protein synthesis to 0.2% of controls only at 192 hr after exposure to 100 LF/ml. The results suggest that human T and B lymphocytes may not be as sensitive to DT protein synthesis inhibition as human fibroblast and Chinese hamster cells. For this reason, Dipr may not be a suitable marker for the somatic cell mutation test.

Cells, Cultured↗
PubMed1982

Environmental chemodynamic studies with terbufos (Counter) insecticide in soil under laboratory and field conditions.

The effect of temperature, soil moisture, soil type, adsorption, and formulation on terbufos persistence in soil was studied under laboratory conditions. Temperature appeared to be more important than moisture in influencing the dissipation rate of terbufos. More terbufos was recovered from a granular formulation than a technical formulation one month after incubation. Soil adsorption coefficient and calculated first order rate constant were well correlated. Terbufos was relatively immobile on soil thin layers and in field-located soil columns. Laboratory data agreed reasonably well with measurements of persistence in the field. Terbufos degradation kinetics were qualitatively analyzed and the toxicological significance of studying parent terbufos alone was discussed.

Organothiophosphorus Compounds↗
PubMed1981

Chromosome-damaging activity of ferritin and its relation to chelation and reduction of iron.

Ferritin from horse spleen was found to cause severe chromosome aberrations in cultured Chinese hamster ovary cells. Ferritin at 15 to 170 microgram/ml was clastogenic and at higher doses was cytotoxic. At comparable concentrations of protein or iron, neither apoferritin nor complexed iron was clastogenic. Sulfhydryl compounds glutathione and cysteine reduced the cytotoxic and clastogenic activities of ferritin. Physiological concentrations of glutathione may normally be sufficient to protect cells from damage. The reducing agent ascorbate had little protective effect. Chelating agents varied in their inhibitory activity: ethylenediaminetetraacetic acid (hexadentate) greater than nitrilotriacetic acid (tetradentate) greater than salicylate (bidentate). 2,2'-Bipyridyl enhance the chromosome-damaging action of ferritin while histidine did not markedly alter the frequencies of aberrations. Catalase and superoxide dismutase showed no inhibitory activity. The mechanism of DNA damage may involve reduction of Fe(III) in the ferritin core to Fe(II), followed by reoxidation of Fe(II) with possible formation of free radicals.

2,2'-Dipyridyl↗