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Biomedical subjects

H Pan

Publications and source records attributed to H Pan.

At least 55 records · Page 3Linked to original sources
PubMed2000

Loss of phosphine from unsealed bins of wheat at six combinations of grain temperature and grain moisture content.

Hard red winter wheat (1.4 t) at 11.1 or 13.5% moisture content (wet basis) and 20, 25, or 30 degrees C was fumigated with tablets of an aluminum phosphide formulation in unsealed, cylindrical grain bins of corrugated metal. The fumigant leakage rate was manipulated to approximate that commonly encountered in farm and commercial-scale bins of this type. Phosphine concentration profiles were recorded and phosphine loss and sorption were characterized to determine which conditions provided the greatest probability of successful fumigation in these bins. Phosphine leakage and sorption were both positively related to grain temperature and moisture content. The fumigant concentration profiles were compared with previously-published data relating temperature to the developmental rate and fumigant susceptibility of lesser grain borer eggs, which are phosphine-resistant but become less resistant as they age. The mean phosphine concentration observed at the time corresponding to one-half of the calculated egg development time was compared to the lethal concentration (LC(99)) for a 2-day exposure at each temperature-moisture combination. In the low-moisture grain at 20 degrees C, the observed fumigant concentration was below the lethal concentration, due to the long development time under these conditions. At 25 and 30 degrees C in the low-moisture wheat, the likelihood of complete kill appeared more favorable because the fumigant concentration remained above the published LC(99) for more than half of the egg development time. In the wheat with 13.5% moisture content, rapid fumigant sorption and loss resulted in phosphine concentrations below the LC(99) at one-half of the development time at 20 or 25 degrees C. At 30 degrees C, due to the very rapid development rate, the observed phosphine concentration exceeded the LC(99) half-way through the egg development period despite the rapid rate of fumigant sorption and loss. Repeated fumigation of the same grain reduced the rate at which phosphine sorbed into the grain.

Journal Article↗
PubMed2000

Activation of intrinsic afferent pathways in submucosal ganglia of the guinea pig small intestine.

The enteric nervous system contains intrinsic primary afferent neurons that allow mucosal stimulation to initiate reflexes without CNS input. We tested the hypothesis that submucosal primary afferent neurons are activated by 5-hydroxytryptamine (5-HT) released from the stimulated mucosa. Fast and/or slow EPSPs were recorded in submucosal neurons after the delivery of exogenous 5-HT, WAY100325 (a 5-HT(1P) agonist), mechanical, or electrical stimuli to the mucosa of myenteric plexus-free preparations (+/- extrinsic denervation). These events were responses of second-order cells to transmitters released by excited primary afferent neurons. After all stimuli, fast and slow EPSPs were abolished by a 5-HT(1P) antagonist, N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide, and by 1.0 microM tropisetron, but not by 5-HT(4)-selective antagonists (SB204070 and GR113808A) or 5-HT(3)-selective antagonists (ondansetron and 0.3 microM tropisetron). Fast EPSPs in second-order neurons were blocked by hexamethonium, and most slow EPSPs were blocked by an antagonist of human calcitonin gene-related peptide (hCGRP(8-37)). hCGRP(8-37) also inhibited the spread of excitation in the submucosal plexus, assessed by measuring the uptake of FM2-10 and induction of c-fos. In summary, data are consistent with the hypothesis that 5-HT from enterochromaffin cells in response to mucosal stimuli initiates reflexes by stimulating 5-HT(1P) receptors on submucosal primary afferent neurons. Second-order neurons respond to these cholinergic/CGRP-containing cells with nicotinic fast EPSPs and/or CGRP-mediated slow EPSPs. Slow EPSPs are necessary for excitation to spread within the submucosal plexus. Because some second-order neurons contain also CGRP, primary afferent neurons may be multifunctional and also serve as interneurons.

Afferent Pathways↗
PubMed2000

The human homolog of insect-derived growth factor, CECR1, is a candidate gene for features of cat eye syndrome.

Cat eye syndrome (CES) is a developmental disorder with multiple organ involvement, associated with the duplication of a 2-Mb region of 22q11.2. Using exon trapping and genomic sequence analysis, we have isolated and characterized a gene, CECR1, that maps to this critical region. The protein encoded by CECR1 is similar to previously identified novel growth factors: IDGF from Sarcophaga peregrina (flesh fly) and MDGF from Aplysia californica (sea hare). The CECR1 gene is alternatively spliced and expressed in numerous tissues, with most abundant expression in human adult heart, lung, lymphoblasts, and placenta as well as fetal lung, liver, and kidney. In situ hybridization of a human embryo shows specific expression in the outflow tract and atrium of the developing heart, the VII/VIII cranial nerve ganglion, and the notochord. The location of this gene in the CES critical region and its embryonic expression suggest that the overexpression of CECR1 may be responsible for at least some features of CES, particularly the heart defects.

Abnormalities, Multiple↗
PubMed2000

Structure of the zinc-binding domain of Bacillus stearothermophilus DNA primase.

BACKGROUND: DNA primases catalyse the synthesis of the short RNA primers that are required for DNA replication by DNA polymerases. Primases comprise three functional domains: a zinc-binding domain that is responsible for template recognition, a polymerase domain, and a domain that interacts with the replicative helicase, DnaB. RESULTS: We present the crystal structure of the zinc-binding domain of DNA primase from Bacillus stearothermophilus, determined at 1.7 A resolution. This is the first high-resolution structural information about any DNA primase. A model is discussed for the interaction of this domain with the single-stranded DNA template. CONCLUSIONS: The structure of the DNA primase zinc-binding domain confirms that the protein belongs to the zinc ribbon subfamily. Structural comparison with other nucleic acid binding proteins suggests that the beta sheet of primase is likely to be the DNA-binding surface, with conserved residues on this surface being involved in the binding and recognition of DNA.

Amino Acid Sequence↗
PubMed2000

Mapping protein-protein interactions within a stable complex of DNA primase and DnaB helicase from Bacillus stearothermophilus.

For the first time, we demonstrate directly a stable complex between a bacterial DnaG (primase) and DnaB (helicase). Utilizing fragments of both proteins, we are able to dissect interactions within this complex and provide direct evidence that it is the C-terminal domain of primase that interacts with DnaB. Furthermore, this C-terminal domain is sufficient to induce maximal stimulation of the helicase and ATPase activities of DnaB. However, the region of DnaB that interacts with the C-terminal domain of primase appears to comprise a surface on DnaB that includes regions from both of the previously identified N- and C-terminal domains. Using a combination of biochemical and physical techniques, we show that the helicase-primase complex comprises one DnaB hexamer and either two or three molecules of DnaG. Our results show that in Bacillus stearothermophilus the helicase-primase interaction at the replication fork may not be transient, as was shown to be the case in Escherichia coli. Instead, primase appears to interact with the helicase forming a tighter complex with enhanced ATPase and helicase activities.

Bacterial Proteins↗
PubMed2000

PRK, a cell cycle gene localized to 8p21, is downregulated in head and neck cancer.

The human PRK gene encodes a protein serine/threonine kinase of the polo family and plays an essential role in regulating meiosis and mitosis. We have previously shown that PRK expression is downregulated in a significant fraction of lung carcinomas. Our current studies reveal that PRK mRNA expression is downregulated in a majority (26 out of 35 patients) of primary head and neck squamous-cell carcinomas (HNSCC) compared with adjacent uninvolved tissues from the same patients, regardless of stage. In addition, PRK transcripts were undetectable in one of the two HNSCC cell lines analyzed. Ectopic expression of PRK, but not a PRK deletion construct, in transformed A549 fibroblast cells suppresses their proliferation. Furthermore, fluorescence in situ hybridization analyses show that the PRK gene localizes to chromosome band 8p21, a region that exhibits a high frequency of loss of heterozygosity in a variety of human cancers, including head and neck cancers, and that is proposed to contain two putative tumor suppressor genes. Considering that PRK plays an important role in the regulation of the G2/M transition and cell cycle progression, our current studies suggest that deregulated expression of PRK may contribute to tumor development. Genes Chromosomes Cancer 27:332-336, 2000.

Carcinoma, Squamous Cell↗
PubMed2000

A CBF-based event-related brain activation paradigm: characterization of impulse-response function and comparison to BOLD.

A perfusion-based event-related functional MRI method for the study of brain activation is presented. In this method, cerebral blood flow (CBF) was measured using a recently developed multislice arterial spin-labeling (ASL) perfusion imaging method with rapid spiral scanning. Temporal resolution of the perfusion measurement was substantially improved by employing intertrial subtraction and stimulus-shifting schemes. Perfusion and blood oxygenation level-dependent (BOLD) signals were obtained simultaneously by subtracting or adding the control and labeled images, respectively, in the same data sets. The impulse response function (IRF) of perfusion during brain activation was characterized for multiple stimulus durations and compared to the simultaneously acquired BOLD response. The CBF response curve preceded the BOLD curve by 0.21 s in the rising phase and 0.64 s in the falling phase. Linear additivity of the CBF and BOLD responses was assessed with rapidly repeated stimulations within single trials, and departure from linearity was found in both responses, characterized as attenuated amplitude and delayed rising time. Event-related visual and sensorimotor activation experiments were successfully performed with the new perfusion technique.

Brain↗
PubMed2000

Sequence-specific transcriptional corepressor function for BRCA1 through a novel zinc finger protein, ZBRK1.

BRCA1 has been implicated in the transcriptional regulation of DNA damage-inducible genes that function in cell cycle arrest. To explore the mechanistic basis for this regulation, a novel human gene, ZBRK1, which encodes a 60 kDa protein with an N-terminal KRAB domain and eight central zinc fingers, was identified by virtue of its interaction with BRCA1 in vitro and in vivo. ZBRK1 binds to a specific sequence, GGGxxx CAGxxxTTT, within GADD45 intron 3 that supports the assembly of a nuclear complex minimally containing both ZBRK1 and BRCA1. ZBRK1 represses transcription through this recognition sequence in a BRCA1-dependent manner. These results thus reveal a novel corepressor function for BRCA1 and provide a mechanistic basis for the biological activity of BRCA1 through sequence-specific transcriptional regulation.

Amino Acid Sequence↗
PubMed2000

High resolution computed tomography and MRI for monitoring lung tumor growth in mice undergoing radioimmunotherapy: correlation with histology.

A model lung tumor system has been developed in mice for the evaluation of vascular targeted radioimmunotherapy. In this model, EMT-6 mammary carcinoma tumors growing in the lung are treated with 213Bi, an alpha particle emitter, which is targeted to lung blood vessels using a monoclonal antibody. Smaller tumors (< 100 microm in diameter) are cured, but larger tumors undergo a period of regression and then regrow and ultimately prove lethal. The goal of this work was to determine if external imaging with MRI or CT could be used routinely to monitor the growth/ regression of lung tumors in live mice. To attempt to evaluate individual tumors in vivo, animals were initially imaged with magnetic resonance imaging (MRI). High resolution MRI images could be obtained only after sacrifice when lungs were not moving. In contrast, high resolution computed tomography (CT) produced evaluable images from anesthetized animals. Serial CT images (up to 5/animal) were collected over a 17 day period of tumor growth and treatment. When tumored animals became moribund, animals were sacrificed and lungs were inflated with fixative, embedded in paraffin, and then sectioned serially to compare the detection of tumors by high resolution CT with detection by histology. CT proved most useful in detecting lung tumors located in the hilar area and least useful in detecting serosal surface and anterior lobe tumor foci. Overall, CT images of live animals revealed tumors in approximately 2/3 of cases detected in histologic serial sections when relatively few tumors were present per lung. Detection of lesions and their resolution post therapy were complicated due to residual hemorrhagic, regressing tumor nodules and the development of lung edema both of which appeared as high density areas in the CT scans. We conclude that the microCT method used could identify some lung tumors as small as 100 microm in diameter; however, no concrete evaluation of therapy induced regression of the tumors could be made with CT analyses alone.

Animals↗
PubMed2000

[The diploid of genetically engineered yeast for expression of hybrid HBsAg gene SA-28].

By mating a yeast haploid expressing hybrid HBsAg gene SA-28, Y19/YFD158, with another hapolid Y95, the diploid Y95xY19/YFD158 was constructed. The experiments showed that the cell density of the diploid in fermentation was three time higher than that of the haploid, the stability of expression vector in the diploid was much higher than in the haploid, the xpression level of hybrid HBsAg gene of the diploid was more than three time higher than that of the haploid and the average cope number in diploid cell was a little lower than that in the haploid.

Diploidy↗
PubMed2000

[Effects of gene copy number and chromosomal position on the expression of a modified HBsAg gene SA-28 in yeast].

The effect of gene copy number and chromosomal position on heterologous gene expression in Saccharomyces cerevisae has been tentatively investigated using a modified hepatitis B virus surface antigen SA-28 gene. The plasmids containing different copies of SA-28 gene expression cassette were integrated into different chromosomal loci via FLP recombinase mediated targeted integration. The expression of SA-28 gene in the resultant transformants was then measured. The result indicated that the expression of SA-28 gene was positively related to the gene dosage at HIS3 locus and had chromosomal polarity at several chromosomal loci.

Chromosome Mapping↗
PubMed2000

[Using multiplex PCR for the detection of virulence genes in Escherichia coli O157:H7].

OBJECTIVE: To detect and characterize the virulence genes in E. coli O157:H7 isolated from various reservoir in six areas of Jiangsu province. METHOD: The virulence genes of Shiga-like toxin (SLT(1) and SLT(2)), intimin (eaeA) and hemolysin (hlyA) were chosen as the target genes and amplified in multiplex PCR assays. RESULTS: Of the eighty-five E. coli O157:H7 strains, the overall virulence gene prevalence was found to be 56.5% (48/85). The prevalence rates virulence genes of isolates from various areas were different from 0% up to 90.5%. It seemed to exist a relationship between the virulence gene prevalence and the level of incidence. In the areas where rates of incidence were divided into high, low, sporadic or zero, the prevalence rates were 85.7% (36/42), 52.6% (10/19) and 8.3% (2/24), respectively. The prevalence rates of isolates were also different from various reservoirs, decreasing by sheep, cattle, pig and poultry. One isolate from a rabbit was positive for SLT(2), eaeA and hly genes. Of forty-eight isolates carrying virulence genes, 38 (79.2%) had SLT(2), eaeA and hly genes, taking the dominate virulence gene pattern, 8 (16.6%) had all of the four virulence genes 2 (4.2%) had both SLT(2) and hly genes respectively. In addition, SLT(1) gene showed a lower prevalence, which was different from some findings abroad. CONCLUSION: Since virulence gene pattern of E. coli O157:H7 is an important molecular epidemiological marker, it can provide an useful information for epidemiologic studies, and helpful to the design of prevention and control strategies. For virulence gene detection, multiplex PCR seems to be a simple, rapid, specific and sensitive method.

Adhesins, Bacterial↗
PubMed2000

[A study on relationship between plasma heat stress protein 70 and cytokine in patients with heat apoplexy].

OBJECTIVE: To study the change of levels of plasma heat stress protein 70 (HSP70) and cytokine and their interrelationship in pathogenicity of heat apoplexy. METHODS: Plasma HSP70 was determined with Western blot, and plasma interleukin-2 (IL-2), soluble interleukin-2 receptor (sIL-2R) and interleukin-6 (IL-6) were determined with enzyme-linked immunosorbent assay (ELISA). RESULTS: Plasma level of HSP70 was 4 211.2 +/- 1,286.2 (integral optical density) in average in the patients of heat apoplexy group, 4,137.8 +/- 1, 207.5 in those of severe heat apoplexy group, and 6,043.5 +/- 1,354.8 in control group, with very significant difference (P < 0.01). Plasma IL-2 level was (64.3 +/- 32.3) pg/ml and (200.0 +/- 50.0) pg/ml and sIL-2R (54.9 +/- 33.3) U/ml and (167.5 +/- 89.0) U/ml in the patients with heat apoplexy and in controls, respectively, with very significant difference. But, there was no significant difference in IL-6 between varied groups. CONCLUSIONS: The above-mentioned results suggest that establishment of heat acclimatization correlates to the interaction of network of neuroendocrine-cytokine-HSP, in which decrease in plasma IL-2 was one of the important factors causing reduction of HSP70 expression. Balance of network regulation was broken by pathological factors, finally resulting in heat apoplexy.

Adolescent↗
PubMed2000

[Diagnosis of PNH by detecting the resistance of RBCs to the hemolytic effect of hec toxin secreted by Aeromonus hydrophila].

OBJECTIVE: To study the feasibility of diagnosing paroxysmal nocturnal hemoglobinuria (PNH) with hec toxin (secreted by Aeromonus hydrophila) test. METHODS: The crude hec toxin was extracted from the culture medium of Aeromonus hydrophila by precipitating with saturated (NH(4))(2)SO(4) and then purified through DEAE52. This crude hec toxin was used to act on red blood cells (RBCs) from patients with PNH, non-PNH anemias, and normal persons. Absorbance at 630nm was measured to quantitate the extent of hemolysis. Hec treated and untreated RBCs were both stained with anti CD(59) monoclonal antibody and FITC labelled goat-anti-mouse IgG. The percentage of CD(59)(+) cells was detected by flow cytometry. RESULTS: After hec toxin treatment, RBCs from PNH patients showed resistance to the toxin hemolysis, which was negatively related to the CD(59)(+) cells percentage, while RBCs from non-PNH were lysed totally. CONCLUSION: RBCs from PNH have obvious resistance to the hemolytic effect of hec toxin, and the percentage of remained unhemolytic cells reflect the severity of PNH. Resistance detection of RBCs to hec toxin can be used for the diagnosis of PNH.

Bacterial Toxins↗
PubMed2000

[FTIR spectra of SO4(2-)/Fe2O3 nanosolid superacid].

The nanosolid superacid SO4(2-)/Fe2O3 was prepared by using nanometer chemical precursor FeO(OH)2 put in the SO4(2-) solution and dried. IR spectra of samples was determined with different calcination temperature, calcination time and with different concentration SO4(2-) solutions. They are different from IR of normal solid superacid. Then a good analysis and discussion are done.

English Abstract↗
PubMed1999

The physical association and phosphorylation of Cdc25C protein phosphatase by Prk.

prk encodes a protein serine/threonine kinase involved in regulating M phase functions during the cell cycle. We have expressed His6-Prk and His6-Cdc25C proteins using the baculoviral vector expression system. Purified recombinant His6-Prk, but not a kinase-defective mutant His6-PrkK52R, is capable of strongly phosphorylating His6-Cdc25C in vitro. Co-immunoprecipitation and affinity column chromatography experiments demonstrate that GST-Prk and native Cdc25C interact. When co-infected with His6-Prk and His6-Cdc25C recombinant baculoviruses, sf-9 cells produce His6-Cdc25C antigen with an additional slower mobility band on denaturing polyacrylamide gels compared with cells infected with His6-Cdc25C baculovirus alone. In addition, His6-Cdc25C immunoprecipitated from sf-9 cells co-infected with His6-Prk and His6-Cdc25C baculoviruses, but not with His6-PrkK52R and His6-Cdc25C baculoviruses, contains a greatly enhanced kinase activity that phosphorylates His6-Cdc25C in vitro. Moreover, phosphopeptide mapping shows that His6-Prk phosphorylates His6-Cdc25C at two sites in vitro and that the major phosphorylation site co-migrates with the one that is phosphorylated in vivo in asynchonized cells. Further studies reveal that His6-Prk phosphorylates Cdc25C on serine216, a residue also phosphorylated by Chk1 and Chk2. Together, these observations strongly suggest that Prk's role in mitosis is at least partly mediated through direct regulation of Cdc25C.

Animals↗
PubMed1999

Cloning, expression and biochemical characterization of a basic-acidic hybrid phospholipase A2-II from Agkistrodon halys pallas.

A cDNA encoding a basic-acidic hybrid phospholipase A2-II from Agkistrodon halys Pallas with an N-terminus highly homologous to that of BPLA2 and a C-terminus sequence almost the same as that of APLA2 was inserted into a bacterial expression vector and effectively expressed in Escherichia coli RR1. The protein was produced as insoluble inclusion bodies. After partial purification by washing, the inclusion bodies with Triton X-100, denaturing and refolding, the renatured recombinant protein was purified by FPLC column superose 12. The purified recombinant enzyme with an isoelectric point of pH 6.8 could cross-react with antiserum prepared against acidic phospholipase A2. The enzymatic activity of the expressed basic-acidic hybrid phospholipase A2-II is close to that of denatured-refolded native basic phospholipase A2, and has the same inhibiting effect on platelet aggregation as denatured-refolded acidic phospholipase A2, but lacks the hemolytic activity of denatured-refolded basic phospholipase A2. To study the structural relationships among basic phospholipase A2, acidic phospholipase A2 and basic-acidic hybrid phospholipase A2-II, molecular modeling of basic-acidic hybrid phospholipase A2-II was done. The roles of various amino acid residues in the enzymatic activity and pharmacological activities of phospholipase A2 are discussed.

Agkistrodon↗