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Biomedical subjects

Q Xu

Publications and source records attributed to Q Xu.

At least 397 records · Page 22Linked to original sources
PubMed1994

Targeted deletion of psaJ from the cyanobacterium Synechocystis sp. PCC 6803 indicates structural interactions between the PsaJ and PsaF subunits of photosystem I.

Photosystem I catalyzes the light-driven oxidation of plastocyanin or cytochrome c6 and the reduction of ferredoxin or flavodoxin. PsaJ is a 4.4 kDa hydrophobic subunit of photosystem I from cyanobacteria and chloroplasts. To investigate the function of PsaJ, we generated a mutant strain of the cyanobacterium Synechocystis sp. PCC 6803 in which the psaJ gene is replaced by a gene for chloramphenicol resistance. Deletion of psaJ led to a reduction in the steady state RNA level from psaF which is located upstream from psaJ. Immunoquantification using an anti-PsaF antibody revealed a significant decrease in the amount of PsaF in membranes of the mutant strain. Trimeric photosystem I complexes isolated from the mutant strain using n-dodecyl beta-D-maltoside lacked PsaJ, contained ca. 80% less PsaF, but maintained wild-type levels of other photosystem I subunits. In contrast, the photosystem I purified using Triton X-100 contained less than 2% PsaF when compared to the wild type, showing the more extractable nature of PsaF in PsaJ-less photosystem I in the presence of Triton X-100. PsaE was more accessible to removal by NaI in a mutant strain lacking PsaF and PsaJ than in the wild type. The presence of PsaF in photosystem I from the PsaJ-less strain did not alter the increased susceptibility of PsaE to removal by NaI. These results indicate an interaction between PsaJ and PsaF in the organization of the complex.

Bacterial Proteins↗
PubMed1994

Study of a low-selenium environment in China by INAA and Mössbauer spectrometry.

The neutron activation analysis, gamma coincidence spectroscopy, nondispersive hydrogen flame atomic fluorescence spectroscopy, and Mössbauer spectrometry were used to study the low-selenium environment of the Exi Autonomous Prefecture, a well-known Keshan disease region. The Se contents in the soil samples there range from 0.075-0.18 mg/kg with the average of 0.13 mg/kg, whereas in the maize from 0.001-0.018 mg/kg with the average of 0.0099 mg/kg. The 57Fe Mössbauer spectrum of the soil indicates an anoxic environment. In addition to the FE3+ species the compounds containing low-valence iron e.g., goethite, and so forth, also exist. The rare earth element (REE) pattern obtained by NAA further confirms the reductive soil environment, which causes the selenium deficiency.

China↗
PubMed1994

Synthesis, characterization, and antitumor activity of amine platinum(II) and (IV) tellurate complexes.

A series of novel water-soluble amine platinum (II) tellurate complexes of the type (A)Pt(II) [TeO2(OH)4], where A = 1,2-diaminocyclohexane (DACH), 1,1-bis(aminomethyl)cyclohexane (AMCH), ethylenediamine (en), or cyclopentylamine (cpa), were prepared either by the reaction of amineplatinum (II) sulfate with barium tellurate or by a direct reaction of (A)Pt(OH)2 with telluric acid. Oxidation of the amine platinum(II) tellurate produced amine platinum(IV) tellurate (A)Pt(IV)trans(Z) [TeO2(OH)4] complexes, where Z = OH or Cl, following oxidation with hydrogen peroxide or with chlorine gas, respectively. Complexes were characterized by elemental analysis, and IR and 195Pt NMR spectroscopy. Against i.p. murine leukemia cells in vivo, some of the complexes displayed good antitumor activity when administered intraperitoneally (i.p.) on days 1, 5, and 9 at their optimal doses. Pt(II) complexes containing R,R-DACH, S,S-DACH, R,R-S,S-DACH, or AMCH produced %T/C of 147 to 288 whereas cis-DACH, en, and cpa complexes were inactive. In the Pt(IV) series, the R,R-DACH complex with axial Cl was highly active (%T/C = 371, 40% cures) compared with the complex with axial OH (%T/C = 135).

Amines↗
PubMed1994

Regulatory gene expression boundaries demarcate sites of neuronal differentiation in the embryonic zebrafish forebrain.

During development of the zebrafish forebrain, a simple scaffold of axon pathways is pioneered by a small number of neurons. We show that boundaries of expression domains of members of the eph, forkhead, pax, and wnt gene families correlate with the positions at which these neurons differentiate and extend axons. Analysis of genetically or experimentally altered forebrains indicates that if a boundary is maintained, there is appropriate neural differentiation with respect to the boundary. Conversely, in the absence of a boundary, there is concomitant disruption of neural patterning. We also show that a strip of cells within the dorsal diencephalon shares features with ventral midline cells. This strip of cells fails to develop in mutant fish in which specification of the ventral CNS is disrupted, suggesting that its development may be regulated by the same inductive pathways that pattern the ventral midline.

Animals↗
PubMed1994

Optimal batch size for estimation of the prevalence of a disease using combined samples.

Great attention has been given to the combined sample test for its high efficiency. Here a model of mathematical expectation for combined samples has been worked out and used for investigating the prevalence of HCV in serum from blood donors. It was shown that this model was valuable if the probability of a positive test, e.g. the prevalence, is less than 0.31.

Blood Donors↗
PubMed1994

Identification of surface-exposed domains on the reducing side of photosystem I.

Photosystem I (PSI) is a multisubunit enzyme that catalyzes the light-driven oxidation of plastocyanin or cytochrome c6 and the concomitant photoreduction of ferredoxin or flavodoxin. To identify the surface-exposed domains in PSI of the cyanobacterium Synechocystis sp. PCC 6803, we mapped the regions in PsaE, PsaD, and PsaF that are accessible to proteases and N-hydroxysuccinimidobiotin (NHS-biotin). Upon exposure of PSI complexes to a low concentration of endoproteinase glutamic acid (Glu)-C, PsaE was cleaved to 7.1- and 6.6-kD N-terminal fragments without significant cleavage of other subunits. Glu63 and Glu67, located near the C terminus of PsaE, were the most likely cleavage sites. At higher protease concentrations, the PsaE fragments were further cleaved and an N-terminal 9.8-kD PsaD fragment accumulated, demonstrating the accessibility of Glu residue(s) in the C-terminal domain of PsaD to the protease. Besides these major, primary cleavage products, several secondary cleavage sites on PsaD, PsaE, and PsaF were also identified. PsaF resisted proteolysis when PsaD and PsaE were intact. Glu88 and Glu124 of PsaF became susceptible to endoproteinase Glu-C upon extensive cleavage of PsaD and PsaE. Modification of PSI proteins with NHS-biotin and subsequent cleavage by endoproteinase Glu-C or thermolysin showed that the intact PsaE and PsaD, but not their major degradation products lacking C-terminal domains, were heavily biotinylated. Therefore, lysine-74 at the C terminus of PsaE was accessible for biotinylation. Similarly, lysine-107, or lysine-118, or both in PsaD could be modified by NHS-biotin.

Amino Acid Sequence↗
PubMed1994

Surface staining and cytotoxic activity of heat-shock protein 60 antibody in stressed aortic endothelial cells.

Heat-shock protein (hsp) expression can be induced by high temperature, exposure to cytokines or oxygen radicals, ischemia, hemodynamic overload, or viral infections. To determine whether surface expression of hsp60 occurs in aortic endothelial cells stressed by high temperature or cytokines, cells from rat aortas were cultivated and stained with several types of monoclonal antibodies against hsp60. Other antibodies, eg, those against intercellular adhesion molecule-1 (ICAM-1), or immune response-associated antigens were also used as controls. Positive staining of endothelial cells on the surface and in the cytoplasm was observed after pretreatment of the cells with cytokine-containing medium, tumor necrosis factor-alpha (TNF-alpha), or interleukin-1 alpha and labeling with a specific monoclonal antibody against hsp60 (II-13). Fluorescence-activated cell sorter analyses showed that over 80% of living endothelial cells stressed by cytokine-containing medium, by TNF-alpha, or at 42 degrees C, but not by interleukin-1 alpha, were positively surface stained with this antibody. Increased intensity of immunostaining with antibodies to ICAM-1 and immune response-associated antigen was also seen on the cytokine-stressed endothelial cells. Furthermore, when TNF-alpha stimulated endothelial cells labeled with 51Cr were incubated with antibody II-13 in the presence of complement, significant lysis occurred. In summary, endothelial cells stressed by high temperature or certain cytokines, eg, TNF-alpha, express hsp60 in the cytoplasm and on their surfaces, and these cells were susceptible to complement-dependent lysis by hsp60-specific antibody. These observations may be significant for elucidating the mechanisms of the involvement of immune reactions to hsp65/60 in initiating atherosclerosis.

Animals↗
PubMed1994

Effect of moderate hypothermia on lipid peroxidation in canine brain tissue after cardiac arrest and resuscitation.

BACKGROUND AND PURPOSE: We sought to examine the effect of moderate hypothermia (30 degrees C to 32 degrees C) initiated after resuscitation on the scavenging systems of free radicals and lipid peroxidation in canine brain tissue after cardiac arrest and resuscitation. METHODS: Twenty-one dogs were divided into four groups: group A, nonischemic controls (shams) (n = 4); group B, 15-minute cardiac arrest without reperfusion (n = 4); group C, 15-minute cardiac arrest and standard resuscitation (n = 6); and group D, 15-minute cardiac arrest and hypothermic resuscitation (n = 7). During the period of 10 to 120 minutes after resuscitation, brain temperature and core temperature in group D remained at 30 degrees C to 32 degrees C and were 4 degrees C to 5 degrees C lower than in group C. For each dog, a sample of right parietal cerebral cortex was obtained from group A, group B, or from group C and group D at 2 hours after resuscitation. The sample was assayed for tissue malondialdehyde (MDA), the content of reduced glutathione (GSH), and the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX). RESULTS: In group B, a 15-minute cardiac arrest induced an increase in MDA, a significant reduction of GSH, and no change in SOD and GSH-PX activities compared with group A. In group C, there were further increases in MDA and reductions in GSH content and GSH-PX activity compared with group A; SOD activity remained substantially unchanged. The content of MDA was higher in group D than in group A but less elevated in group D than in group C. The GSH content and SOD and GSH-PX activities were significantly higher in group D than in group C. CONCLUSIONS: Moderate hypothermia initiated after resuscitation can significantly inhibit the accumulation of lipid peroxidation products and the consumption of free radical scavengers in the brain tissue.

Animals↗
PubMed1994

Spatially regulated expression of three receptor tyrosine kinase genes during gastrulation in the zebrafish.

We describe the isolation and early developmental expression of three novel zebrafish genes (rtk1-3) that encode members of the eph family of receptor tyrosine kinases. At the onset of gastrulation, rtk1 is expressed in the shield region corresponding to the future dorsal side of the embryo. As gastrulation proceeds, both rtk1 and rtk2 are expressed within the axial hypoblast along the entire axis of the embryo. After the gastrula stage is complete, expression of both genes is maintained in precursor cells of the notochord in the tail bud but is downregulated in other regions of the axial hypoblast, rtk3 is expressed in anterior axial hypoblast including the 'pillow' at the anterior tip of the hypoblast and in paraxial tissue in posterior regions of the embryo. We show that the precise spatial regulation of expression of rtk genes, ntl and goosecoid along the anteroposterior axis is maintained in embryos that have no dorsoventral axis. This indicates that the mechanisms that regulate gene expression along the anteroposterior and dorsoventral axes of the hypoblast may be independent.

Amino Acid Sequence↗
PubMed1993

Selective localization and rotational immobilization of univalent cations on quadruplex DNA.

The quadruplex structure of the oligomer d(T2G4T) is more stable in the presence of K+ than in the presence of Na+. This enhanced stability correlates with the preferential binding of K+ to a small number of specific sites on the quadruplex. In contrast, Na+ and K+ compete on an equal footing for atmospheric binding. Both 39K+ and 23Na+ are, when specifically bound, significantly inhibited in their rotational mobility, so that the quadrupolar relaxation reflects the molecular tumbling of the oligomer, which occurs on the time scale of nanoseconds. This rotational immobilization is in distinct contrast to the high rotational mobility of atmospherically bound cations. On the other hand, all NMR-visible 39K+ in solution is in rapid exchange among all environments (free, specifically bound, and atmospherically bound) implying that the lifetime of specifically coordinated 39K+ must be significantly shorter than a millisecond. A similar conclusion holds for 23Na+. The oligomer d(T2G4T) forms two distinct Hoogsteen base-paired structures in NaCl solution, separated by a large kinetic barrier. Neither of these structures is as stable with respect to base pair opening as is the quadruplex structure formed in KCl solution. Only one of these two structures is associated with rotational immobilization of bound 23Na+.

Cations, Monovalent↗
PubMed1993

Rotational dynamics of hexaamminecobalt(III) bound to oligomeric DNA: correlation with cation-induced structural transitions.

Two common assumptions are that duplex DNA structure shows little sensitivity to ionic conditions and that simple cations bind to DNA in a nonspecific fashion. Here we examine these assumptions using as a model ligand the inorganic cation Co(NH3)6(3+). We find, upon titration with Co(NH3)6(3+), that certain DNA oligonucleotides show pronounced changes in circular dichroism spectra. For oligonucleotides such as d(GGCCGGCC), with contiguous, same-strand guanines, the transition is toward A-DNA characteristics. For those oligonucleotides that manifest such large Co(NH3)6(3+)-induced changes in circular dichroism spectra, 59Co NMR relaxation measurements demonstrate that Co(NH3)6(3+) tumbling motions are greatly inhibited, so that the effective NMR correlation time approaches that of overall tumbling of the DNA oligomer. Very large upfield 59Co chemical shifts are observed for Co(NH3)6(3+) bound to such oligonucleotides. For another class of oligomers, which show no significant changes in the circular dichroism spectrum in the presence of Co(NH3)6(3+), the tumbling motions of bound Co(NH3)6(3+) are largely independent of those of the oligomer, and much more modest 59Co chemical shifts are observed. Oligomers in a third class cause significant rotational inhibition of bound Co(NH3)6(3+), and only modest changes in 59Co chemical shifts. Oligonucleotides in this class appear not to undergo large structural changes in the presence of Co(NH3)6(3+). Within these broad categories, a remarkable variability in 59Co NMR parameters, and in structural perturbations, is apparent for the 13 oligonucleotides that we have examined.

Antineoplastic Agents↗
PubMed1993

X-ray crystal structure of tetrachloro(trans-d,l-1,2-diaminocyclohexane) platinum(IV) complex: a potential anticancer agent.

Tetrachloro(trans-d,l-1,2-diaminocyclohexane)platinum(IV) complex (tetraplatin or ormaplatin) has been recognized as a potential anticancer agent. We have determined the crystal structure of this compound by x-ray single crystal diffraction. It has a unique space group and rare molecular packing. Parameters are as follows: space group R3c (rhombohedral), a = 26.425(4) A, alpha = 54.50(1) degrees; V = 11375A3, Z = 36. The coordination about Pt atoms is a slightly distorted octahedron owing to the presence of the geometrically strained five-membered ring (avg. N-Pt-N angle = 82.9 degrees). An intricate network of intermolecular hydrogen bonds holds the crystal lattice together. Three independent ormaplatin molecules surround each water molecule, forming the three shortest A...B contacts and thus the three strongest hydrogen bonds.

Antineoplastic Agents↗
PubMed1993

Targeted inactivation of the gene psaL encoding a subunit of photosystem I of the cyanobacterium Synechocystis sp. PCC 6803.

Photosystem I is a multisubunit pigment-protein complex that functions as a light-driven plastocyanin-ferredoxin oxidoreductase in thylakoid membranes of cyanobacteria and higher plants. A 16-kDa protein subunit of photosystem I complex was isolated from the cyanobacterium Synechocystis sp. PCC 6803. The sequence of its NH2-terminal residues was determined and a corresponding oligonucleotide probe was used to isolate the gene encoding this subunit. The gene, designated as psaL, codes for a protein of 16,605 Da. The deduced amino acid sequence is homologous to the subunit PsaL of barley photosystem I. There are two conserved hydrophobic regions in the subunit PsaL that may cross or interact with thylakoid membranes. The gene psaL exists as a single copy in the genome and is expressed as a monocistronic RNA. Stable mutant strains in which the gene psaL was interrupted by a gene conferring resistance to chloramphenicol, were generated by targeted mutagenesis. Growth and photosynthetic characteristics of a selected mutant strain under photoautotrophic conditions were similar to those of the wild type, suggesting that the function of PsaL is dispensable for photosynthesis in Synechocystis sp. PCC 6803. Western analysis and subunit composition of purified photosystem I revealed that the mutant strain contained other subunits of photosystem I in thylakoid membranes and in the assembled complex. When photosystem II activity was inhibited and glucose was supplied in the medium, mutant strains grew faster than the wild type. Under these conditions of growth, re-reduction of P700 in the mutant cells, but not in the wild type cells, showed a component with an uncharacteristically rapid half-time.

Amino Acid Sequence↗
PubMed1993

Developmental and hormonal regulation of the Xenopus liver-type arginase gene.

Liver-type L-arginase is a major urea-cycle enzyme which is strongly induced during amphibian metamorphosis, but little is known about the molecular mechanisms underlying this induction. As a first step towards elucidating the possible mechanisms, we have isolated a cDNA clone for L-arginase from an adult Xenopus laevis liver cDNA library. Sequence comparison of Xenopus liver-type L-arginase cDNA shows a strong conservation at the amino acid level with those of human, rat and yeast. Using a Xenopus arginase cDNA fragment as a hybridization probe, we have shown by Northern blotting that the gene is highly expressed in the liver, and very slightly in kidney and spleen, of adult Xenopus. The expression is developmentally regulated. Only traces of arginase mRNA can be detected in pre-metamorphic tadpoles, but its accumulation increases very markedly at the onset of natural metamorphosis, being maintained at a high concentration constitutively upon completion of this developmental process. Amphibian metamorphosis is under the strict control of thyroid hormones. It is therefore significant that exposure of pre-metamorphic tadpoles (at stages before endogenous thyroid hormone secretion) to exogenous hormone (1 nM triiodothyronine) precociously activated the L-arginase gene. The time course of this precocious hormonal induction paralleled that of serum albumin gene in the liver. Polyclonal antibodies were raised against recombinant Xenopus L-arginase expressed in Escherichia coli as a fusion protein with glutathione S-transferase in the plasmid expression vector pGEX. Western blotting using this antibody showed that, although arginase mRNA is present in high concentration in Xenopus tadpole liver at the onset of natural metamorphosis, the protein is detected only upon its completion. Our results show a complex transcriptional and post-transcriptional regulation of the Xenopus liver-type L-arginase gene during post-embryonic development. They also demonstrate that this gene can be exploited as a target for thyroid hormones in further studies to analyze the mechanisms underlying the establishment of the adult phenotype during amphibian metamorphosis.

Amino Acid Sequence↗