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171.
Pérez AJ Perez-Iratxeta C Bork P Thode G Andrade MA 《Bioinformatics (Oxford, England)》2004,20(13):2084-2091
172.
Cabrerizo FM Dántola ML Thomas AH Lorente C Braun AM Oliveros E Capparelli AL 《化学与生物多样性》2004,1(11):1800-1811
Studies of the photochemical reactivity of pterin (= 2-aminopteridin-4(3H)-one; PT) in acidic (pH 5.0-6.0) and alkaline (pH 10.2-10.8) aqueous solutions have been performed. The photochemical reactions were followed by UV/VIS spectrophotometry, thin layer chromatography (TLC), high-performance liquid chromatography (HPLC), and an enzymatic method for H2O2 determination. PT is not light-sensitive in the absence of molecular oxygen, but it undergoes photooxidation in the presence of O2, yielding several nonpteridinic products. The quantum yields for PT disappearance were found to be 8.2 (+/-0.6) x 10(-4) and 1.2 (+/-0.2) x 10(-3) in acidic and alkaline media, respectively. H2O2 was detected and quantified in irradiated solutions of PT; and its importance from a biomedical point of view is discussed. The rate constant of the chemical reaction between singlet oxygen ((1)O2) and PT was determined to be 2.5 (+/-0.2) x 10(5) l mol(-1) s(-1) in alkaline medium, and the role of (1)O2 in the photooxidation of pterin was evaluated. 相似文献
173.
Stability of enzymes and proteins in dried glassy systems: effect of simulated sunlight conditions 总被引:2,自引:0,他引:2
The purpose of the present work was to study the effects of simulated sunlight conditions on enzyme inactivation and structural damage in dehydrated glassy systems. Freeze-dried samples containing different enzymes (lactase, invertase, lysozyme and amyloglucosidase) were exposed to light using a medium-pressure metal halide HPA 400 W lamp. After 1 h of light exposure, the samples showed a significant reduction (more than 50%) in the denaturation peak area as analyzed by DSC, and this could be attributed to protein denaturation. For most of the pure enzymes, the loss of enzymic activity after 1 h of light exposure was around 50%. In the case of enzymes included in anhydrous model systems (trehalose, raffinose, maltodextrin, and dextran), the remaining activity also decreased dramatically during the light treatment. We showed that the light exposure in dehydrated systems generated both the loss of enzymic activity and structural changes such as denaturation (observed by DSC) and protein fragmentation and aggregation (observed by electrophoresis). Overall, we can conclude that a short exposure to the light produces dramatic changes in the enzymic activity in dehydrated systems with or without protective matrices. 相似文献
174.
The sex pheromone glands of Lutzomyia cruzi male sand flies (Diptera: Psychodidae) were analyzed by cytochemical techniques. In adult males, the epithelium at the fourth abdominal tergite is modified into a glandular epithelium, with large columnar gland cells located side by side. The gland cell cytoplasm contains a large number of mitochondria and peroxisomes, the latter with positive (electron-dense) reaction for catalase, a typical peroxisomal enzyme marker. The gland cell cytoplasm also contains a central vacuolated area, with a large number of electron-lucent vacuoles, not limited by a unit membrane. In well-preserved preparations such vacuoles present a homogenous and slightly electron-dense content, typical of lipid droplets. Indeed, incubation of the tergites with imidazole-buffered osmium tetroxide (to detect lipids) resulted in positive reaction in these vacuoles, as well as in between the microvilli of the gland cells. Use of the osmium–potassium iodide (Os–KI) technique allowed to demonstrate the presence of several endoplasmic reticulum (ER) profiles, as expected in secretory cells. Our data suggest that ER, lipid droplets and peroxisomes are involved in the sand fly pheromone biosynthesis. 相似文献
175.
Follistatin regulates enamel patterning in mouse incisors by asymmetrically inhibiting BMP signaling and ameloblast differentiation 总被引:3,自引:0,他引:3
Rodent incisors are covered by enamel only on their labial side. This asymmetric distribution of enamel is instrumental to making the cutting edge sharp. Enamel matrix is secreted by ameloblasts derived from dental epithelium. Here we show that overexpression of follistatin in the dental epithelium inhibits ameloblast differentiation in transgenic mouse incisors, whereas in follistatin knockout mice, ameloblasts differentiate ectopically on the lingual enamel-free surface. Consistent with this, in wild-type mice, follistatin was continuously expressed in the lingual dental epithelium but downregulated in the labial epithelium. Experiments on cultured tooth explants indicated that follistatin inhibits the ameloblast-inducing activity of BMP4 from the underlying mesenchymal odontoblasts and that follistatin expression is induced by activin from the surrounding dental follicle. Hence, ameloblast differentiation is regulated by antagonistic actions of BMP4 and activin A from two mesenchymal cell layers flanking the dental epithelium, and asymmetrically expressed follistatin regulates the labial-lingual patterning of enamel formation. 相似文献
176.
Specification of primordial germ cells (PGCs) in the proximal epiblast enables about 45 founder PGCs clustered at the base of the allantoic bud to enter the embryo by active cell movement. Specification of the PGC lineage depends on paracrine signals derived from the somatic cell neighbors in the extraembryonic ectoderm. Secretory bone morphogenetic proteins (BMP) 4, BMP8b, and BMP2 and components of the Smad signaling pathway participate in the specification of PGCs. Cells in the extraembryonic ectoderm induce expression of the gene fragilis in the epiblast in the presence of BMP4, targeting competence of PGCs. The fragilis gene encodes a family of transmembrane proteins presumably involved in homotypic cell adhesion. As PGCs migrate throughout the hindgut, they express nanos3 protein. In the absence of nanos3 gene expression, no germ cells are detected in ovary and testis. During migration and upon arrival at the genital ridges, the population of PGCs is regulated by a balanced proliferation/programmed cell death or apoptosis. Paracrine and autocrine mechanisms, involving transforming growth factor-beta1 and fibroblast growth factors exert stimulatory or inhibitory effects on PGCs proliferation, modulated in part by the membrane-bound form of stem cell factor. Apoptosis requires the participation of the pro-apoptotic family member Bax, whose activity is balanced by the anti-apoptotic family member Bcl21/Bcl-x. In addition, a loss of cell-cell contacts in vitro results in the apoptotic elimination of PGCs. It needs to be determined whether apoptosis is triggered by a failure of PGC to establish and maintain appropriate cell-cell contacts with somatic cells or whether undefined survival factors released by adjacent somatic cells cannot reach physiological levels to satisfy needs of the expanding population of PGCs. 相似文献
177.
Blaisdell CJ Morales MM Andrade AC Bamford P Wasicko M Welling P 《American journal of physiology. Lung cellular and molecular physiology》2004,286(2):L420-L426
Normal lung morphogenesis is dependent on chloride-driven fluid transport. The molecular identity of essential fetal lung chloride channel(s) has not been elucidated. CLC-2 is a chloride channel, which is expressed on the apical surface of the developing respiratory epithelium. CLC-2-like pH-dependent chloride secretion exists in fetal airway cells. We used a 14-day fetal rat lung submersion culture model to examine the role of CLC-2 in lung development. In this model, the excised fetal lung continues to grow, secrete fluid, and become progressively cystic in morphology (26). We inhibited CLC-2 expression in these explants, using antisense oligonucleotides, and found that lung cyst morphology was disrupted. In addition, transepithelial voltage (V(t)) of lung explants transfected with antisense CLC-2 was inhibited with V(t) = -1.5 +/- 0.2 mV (means + SE) compared with -3.7 +/- 0.3 mV (means + SE) for mock-transfected controls and -3.3 +/- 0.3 mV (means + SE) for nonsense oligodeoxynucleotide-transfected controls. This suggests that CLC-2 is important for fetal lung fluid production and that it may play a role in normal lung morphogenesis. 相似文献
178.
Perceiving a possible predator may promote physiological changes to support prey ‘fight or flight’. In this case, an increase in ventilatory frequency (VF) may be expected, because this is a way to improve oxygen uptake for escape tasks. Therefore, changes in VF may be used as a behavioral tool to evaluate visual recognition of a predator threat. Thus, we tested the effects of predator visual exposure on VF in the fish Nile tilapia, Oreochromis niloticus. For this, we measured tilapia VF before and after the presentation of three stimuli: an aquarium with a harmless fish or a predator or water (control). Nile tilapia VF increased significantly in the group visually exposed to a predator compared with the other two, which were similar to each other. Hence, we conclude that Nile tilapia may recognize an allopatric predator; consequently VF is an effective tool to indicate visual recognition of predator threat in fish. 相似文献
179.
Vimentin-positive cells in the epithelium of rabbit ileal villi represent cup cells but not M-cells.
Carolina Ramirez Andreas Gebert 《The journal of histochemistry and cytochemistry》2003,51(11):1533-1544
Membranous (M)-cells are specialized epithelial cells of the Peyer's patch domes that transport antigens from the intestinal lumen to the lymphoid tissue. Vimentin is a reliable marker for M-cells in rabbits. Using immunohistochemistry (IHC), a subpopulation of epithelial cells has recently been identified in ordinary rabbit ileal villi, which are vimentin-positive and share morphological characteristics with the M-cells of the domes. To test the hypothesis that these cells represent M-cells outside the organized lymphoid tissue, lectin labeling and tracer uptake experiments were performed. Lectins specific for N-acetyl-glucosamine oligomers selectively bound to the vimentin-positive villous cells but not to M-cells in the domes. Microbeads instilled into the ileal lumen were taken up by M-cells within 45 min but not by the vimentin-positive cells in the villi. Lectin-gold labeling on ultrathin sections revealed that the lectin binding sites were located in the brush border and in vesicles in the apical cytoplasm. The vimentin/lectin-positive cells shared ultrastructural characteristics with the so-called "cup cells." We conclude (a) that the vimentin-positive cells in ordinary villi represent cup cells but not M-cells, (b) that they are readily detectable by (GlucNAc)(N)-specific lectins, and (c) that they do not transcytose experimental tracers. Although the specific function of cup cells is still obscure, they most probably represent a cell type distinct from M-cells of the domes with respect to both function and expression of the two new markers. 相似文献
180.
The platelet-derived growth factor controls c-myc expression through a JNK- and AP-1-dependent signaling pathway 总被引:2,自引:0,他引:2