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21.
Hamid M. Said Alvaro Ortiz Thomas Y. Ma Eric McCloud 《Journal of cellular physiology》1998,176(3):588-594
The water-soluble vitamin riboflavin (RF) plays a critical role in many metabolic reactions, and thus, is essential for normal cellular functions and growth. The liver plays a central role in normal RF metabolism and is the site of maximal utilization of the vitamin. The mechanism of liver uptake of RF has been studied in animals, but no information is available describing the mechanism of the vitamin uptake in the human situation and its cellular regulation. In this study, we used the human-derived liver cells Hep G2 as an in vitro model system to address these issues. Uptake of RF by Hep G2 cells was found to be temperature- and energy-dependent but Na+-independent in nature. Uptake seemed to involve a carrier-mediated process as indicated by the saturation as a function of substrate concentration (apparent Km 0.41 ± 0.08 μM), and by the ability of the structural analogs lumiflavin and lumichrome to inhibit the uptake process [inhibition constant (Ki) of 1.84 and 6.32 μM, respectively]. RF uptake was energy dependent, and was inhibited by the -SH group blocker p-chloromercuriphenylsulfonate (p-CMPS) (Ki of 0.10 mM). Specific modulators of intracellular protein kinase A (PKA)-, protein kinase C (PKC)-, and protein tyrosine kinase (PTK)-mediated pathways did not affect RF uptake by Hep G2 cells. On the other hand, specific inhibitors of Ca2+/calmodulin-mediated pathway significantly inhibited the uptake process; this effect seemed to be mediated through a decrease in the Vmax of the substrate uptake process. Maintaining Hep G2 cells in a RF-deficient growth medium was associated with a significant up-regulation in the substrate uptake; this effect was specific for RF and was mediated mainly by means of an increase in the Vmax of the uptake process. These results describe, for the first time, the mechanism and cellular regulation of RF uptake by a human-derived liver cellular preparation, and shows the involvement of a carrier-mediated system in the uptake process. Furthermore, the uptake process seems to be regulated by an intracellular Ca2+/calmodulin-mediated pathway and by extracellular substrate levels. J. Cell. Physiol. 176:588–594, 1998. © 1998 Wiley-Liss, Inc. 相似文献
22.
Narrow-leaved plantain (Plantago lanceolata L.), a perennial forb, flowers for virtually the full length of the growing season in temperate latitudes and as a result it is exposed to widely variable intensities of shortwave (UV-B) radiation. In order to determine effects of spring and summer levels of UV-B exposure on growth and development, representatives of 42 maternal families were grown for 85 days at 3.2 and 6.4 kJ m–2 day–1 BE300, levels corresponding to early spring and mid-summer in central Illinois. Impacts on early vegetative stages were most pronounced; early vegetative growth was decreased by higher levels of UV-B and both leaf angle (a measure of erectness) and leaf hair density were increased. At harvest, vegetative growth was significantly affected by higher levels of UV-B as well; the mass of senescent leaves and crown tissue were both decreased. Although exposure to higher levels of UV-B decreased inflorescence number by nearly 15%, it did not significantly alter reproductive biomass. Significant variation attributable to maternal families was present in nearly all measurements and the range of variation among families was wider than among UV-B treatments. A marginally significant (p=0.07) maternal family by UV-B interaction was found for the number of inflorescences, suggesting that, within populations of this plant, some small amount of genetic variation exists to allow for differential reproductive performance under a regime simulating spring and summer differences in UV-B exposure. For the most part, however, in this cosmopolitan species the level of adaptation to natural levels of variation in UV-B radiation does not differ dramatically among maternal families. 相似文献
23.
Daniel Gavino-Leopoldino Camila Menezes Figueiredo Mariana Oliveira Lopes da Silva Letícia Gonalves Barcellos Rmulo Leo Silva Neris Laryssa Daniele Miranda Pinto Suzana Maria Bernardino Araújo Leandro Ladislau Claudia Farias Benjamim Andrea T. Da Poian Julia Rosauro Clarke Claudia Pinto Figueiredo Iranaia Assuno-Miranda 《Journal of virology》2021,95(22)
24.
Richard W. Spjut Charles F. Edson John M. Cassady Tom McCloud Matthew Suffness Daniel H. Norris Gordon M. Cragg 《Economic botany》1988,42(1):62-72
Nine samples of the mossClaopodium crispifolium were collected for large-scale fractionation to isolate antitumor agents. Each sample was active in the P388 Lymphocytic leukemia and KB cell culture, bioassays commonly used to guide the fractionation procedure. Notable variation in the test results among the samples led to re-examination of the voucher samples to determine possible causes. A blue-green alga,Nostoc cf.microscopium, was found to be common on the moss leaves in samples with the best activity. We propose thatNostoc cf.microscopium, or perhaps closely associated organism(s), could be the direct source of the bioactivity, or that the bioactivity could also be a result of allelopathy. 相似文献
25.
Pyruvate kinase (PK, EC 2.7.1.40) was partially purified from the plant cytosolic fraction of N2 -fixing soybean ( Glycine max [L.] Merr.) root nodules. The partially purified PK preparation was completely free of contamination by phospho enol pyruvate carboxylase (PEPC, EC 4.1.1.31), the other major phospho enol pyruvate (PEP)-utilizing enzyme in legume root nodules. Latency experiments with sonicated nodule extracts showed that Bradyrhizobium japonicum bacteroids do not express either PK or PEPC activity in symbiosis. In contrast, free-living B. japonicum bacteria expressed PK activity, but not PEPC activity. Antibodies specific for the cytosolic isoform of PK from castor bean endosperm cross-reacted with a 52-kDa polypeptide in the partially purified PK preparation. At the optimal assay pH (pH 8.0 for PEPC and pH 6.9 for PK) and in the absence of malate, PEPC activity in crude nodule extracts was 2.6 times the corresponding PK activity. This would tend to favour PEP metabolism by PEPC over PEP metabolism by PK. However, at pH 7.0 in the presence of 5 m M malate, PEPC activity was strongly inhibited, but PK activity was unaffected. Thus, we propose that PK and PEPC activity in legume root nodules may be coordinately regulated by fluctuations in malate concentration in the plant cytosolic fraction of the bacteroid-containing cells. Reduced uptake of malate by the bacteroids, as a result of reduced rates of N2 fixation, may favour PEP metabolism by PK over PEP metabolism by PEPC. 相似文献
26.
Darren B Taichman Jennifer Shin Laryssa Hud Christine Archer-Chicko Sandra Kaplan Jeffery S Sager Robert Gallop Jason Christie John Hansen-Flaschen Harold Palevsky 《Respiratory research》2005,6(1):92
Background
Improved outcomes with expanding treatment options for patients with pulmonary arterial hypertension present the opportunity to consider additional end-points in approaching therapy, including factors that influence health-related quality of life. However, comparatively little is known about health-related quality of life and its determinants in patients with pulmonary arterial hypertension.Methods
Health-related quality of life was evaluated in a cross sectional study of 155 outpatients with pulmonary arterial hypertension using generic and respiratory-disease specific measurement tools. Most patients had either World Health Organization functional Class II or III symptoms. Demographic, hemodynamic and treatment variables were assessed for association with health-related quality of life scores.Results
Patients with pulmonary arterial hypertension suffered severe impairments in both physical and emotional domains of health-related quality of life. Patients with idiopathic ("primary") pulmonary arterial hypertension had the best, and those with systemic sclerosis the worst health-related quality of life. Greater six-minute walk distance correlated with better health-related quality of life scores, as did functional Class II versus Class III symptoms. Hemodynamic measurements, however, did not correlate with health-related quality of life scores. No differences in health-related quality of life were found between patients who were being treated with calcium channel antagonists, bosentan or continuously infused epoprostenol at the time of quality of life assessment.Conclusion
Health-related quality of life is severely impaired in patients with pulmonary arterial hypertension and is associated with measures of functional status. Specific associations with impaired health-related quality of life suggest potential areas for targeted intervention. 相似文献27.
Quantification, correlations and manipulations of wound-induced changes in jasmonic acid and nicotine in Nicotiana sylvestris 总被引:10,自引:0,他引:10
Ian T. Baldwin Zong-Ping Zhang Neda Diab Thomas E. Ohnmeiss Eric S. McCloud Gladys Y. Lynds Eric A. Schmelz 《Planta》1997,201(4):397-404
Jasmonic acid (JA) is thought to be part of a signal-transduction pathway which dramatically increases de-novo nicotine synthesis in the roots and increases whole-plant (WP) nicotine pools in response to the wounding of the leaves in
Nicotiana sylvestrisSpegazzini and Comes (Solanaceae). We report the synthesis of a doubly labeled JA ([1, 2-13C]JA) and use it as an internal standard to quantify by gas chromatography-mass spectrometry the changes in root and shoot
JA pools in plants subjected to differing amounts of standardized leaf wounding. Wounding increased JA pools 10-fold locally
in damaged leaves within 90 min and systemically in the roots (3.5-fold) 180 min after wounding. If JA functions as an intermediary
between stimulus and response, quantitative relationships among the stimulus, JA, and the response should exist. To examine
these relationships, we varied the number of punctures in four leaves and quantified both the resulting JA in damaged leaves
after 90 min and the resulting WP nicotine concentration after 5 d. We found statistically significant, positive relationships
among number of leaf punctures, endogenous JA, and WP nicotine accumulation. We used two inhibitors of wound-induced nicotine
production, methyl salicylate and indole-3-acetic acid, to manipulate the relationships between wound-induced changes in JA
and WP nicotine accumulation. Since wounding and the response to wounding occur in widely separated tissues, we applied inhibitors
to different plant parts to examine their effects on the local and systemic components of this response. In all experiments,
inhibition of the wound-induced increase in leaf JA 90 min after wounding was associated with the inhibition of the nicotine
response 5 d after wounding. We conclude that wound-induced increases in leaf JA are an important component of this long-distance
signal-transduction pathway.
Received: 24 April 1996 / Accepted: 18 July 1996 相似文献
28.
Herbivory and caterpillar regurgitants amplify the wound-induced increases in jasmonic acid but not nicotine in Nicotiana sylvestris 总被引:2,自引:0,他引:2
Both herbivory and mechanical damage result in increases in the concentration of the wound-signal molecule, jasmonic acid
(JA), and the defense metabolite, nicotine, in native tobacco plants, Nicotiana sylvestris Speg. et Comes (Solanaceae). We found that higher concentrations of JA resulted from herbivory by Manduca sexta (L.) larvae than from the mechanical damage designed to mimic the herbivory. While both herbivory and mechanical damage increased
JA concentrations in roots of wounded plants, herbivory did not induce either higher root JA or nicotine responses than mechanical
damage. In a separate experiment in which mechanical damage was not designed to mimic herbivory, JA responses to herbivory
were higher than those to mechanical damage, but the whole-plant (WP) nicotine responses were smaller. Furthermore, when regurgitants
from M. sexta larvae were applied to standardized mechanical leaf wounds, leaf JA responses were dramatically amplified. However, neither
the root JA response nor the WP nicotine response was comparably amplified by application of regurgitants. Our findings demonstrate
that the response of N. sylvestris to herbivory is different from its response to mechanical damage; moreover, oral secretions from larvae may be partly responsible
for the difference. During feeding, M. sexta larvae appear to modify the plant's normal defensive response to leaf wounding by reducing the systemic increase in root
JA after leaf damage and the subsequent WP nicotine response.
Received: 28 February 1997 / Accepted: 9 June 1997 相似文献
29.
Using the gene coding for tissue plasminogen activator (tPA) as a reporter gene, a transient gene expression system has been established. Vectors containing the full-length cDNA of tPA with its signal sequences were introduced into mammalian recipient cells by a modified gene transfer procedure. Thirty hours after transfection, the secreted tPA was found in serum-free medium and measured by a fibrin-agarose plate assay (FAPA). In this assay, tPA converts plasminogen into plasmin which then degrades high-Mr fibrin to produce cleared zones. The sizes of these zones correspond to quantities of tPA. The combination of transient tPA expression system and the FAPA provides a quick, sensitive, quantitative and non-destructive method to examine the strength of eukaryotic regulatory elements in tissue-culture cells. 相似文献
30.
Measurement of pulmonary blood flow by fractal analysis of flow heterogeneity in isolated canine lungs 总被引:1,自引:0,他引:1
Barman Scott A.; McCloud Laryssa L.; Catravas John D.; Ehrhart Ina C. 《Journal of applied physiology》1996,81(5):2039-2045
Barman, Scott A., Laryssa L. McCloud, John D. Catravas, andIna C. Ehrhart. Measurement of pulmonary blood flow by fractalanalysis of flow heterogeneity in isolated canine lungs. J. Appl. Physiol. 81(5):2039-2045, 1996.Regional heterogeneity of lung blood flow can bemeasured by analyzing the relative dispersion (RD) of mass(weight)-flow data. Numerous studies have shown that pulmonary bloodflow is fractal in nature, a phenomenon that can be characterized bythe fractal dimension and the RD for the smallest realizable volumeelement (piece size). Although information exists for theapplicability of fractal analysis to pulmonary blood flow in wholeanimal models, little is known in isolated organs. Therefore, thepresent study was done to determine the effect of blood flow rate onthe distribution of pulmonary blood flow in the isolated blood-perfusedcanine lung lobe by using fractal analysis. Four different radiolabeledmicrospheres (141Ce,95Nb,85Sr, and51Cr), each 15 µm in diameter,were injected into the pulmonary lobar artery of isolated canine lunglobes (n = 5) perfused at fourdifferent flow rates ( flow1 = 0.42 ± 0.02 l/min;flow2 = 1.12 ± 0.07 l/min;flow 3 = 2.25 ± 0.17 l/min; flow 4 = 2.59 ± 0.17 l/min), and the pulmonary blood flow distribution was measured. Theresults of the present study indicate that under isogravimetric bloodflow conditions, all regions of horizontally perfused isolated lunglobes received blood flow that was preferentially distributed to themost distal caudal regions of the lobe. Regional pulmonary blood flowin the isolated perfused canine lobe was heterogeneous and fractal innature, as measured by the RD. As flow rates increased, fractal dimension values (averaging 1.22 ± 0.08) remained constant, whereas RD decreased, reflecting more homogeneous blood flowdistribution. At any given blood flow rate, high-flow areas of the lobereceived a proportionally larger amount of regional flow, suggestingthat the degree of pulmonary vascular recruitment may also be spatially related. 相似文献