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241.
Joanne H. Heaton Ellen E. Schilling Thomas D. Gelehrter Matthew M. Rechler Carolyn J. Spencer S. Peter Nissley 《Biochimica et Biophysica Acta (BBA)/General Subjects》1980,632(2):192-203
Insulin stimulates a 2-fold increase in the amount of tyrosine aminotransferase and a 5–10-fold increase in the rate of amino acid transport in dexamethasone-treated rat hepatoma cells. In order to determine whether these effects are mediated by insulin receptors or receptors for insulin-like growth factors, we have examined the binding of 125I-labeled insulin and 125I-labeled multiplication-stimulating activity, a prototype insulin-like growth factor, and compared the biological effects of these polypeptides. Insulin and multiplication-stimulating activity cause an identical increase in transaminase activity and transport velocity; half-maximal biological effects were observed at 35 ng/ml (5.5 nM) insulin and 140 ng/ml multiplication-stimulating activity. The hepatoma cells display typical insulin receptors of appropriate specificity; half-maximal displacement of tracer insulin binding occured at 33 ng/ml unlabeled insulin, but only at 2500 ng/ml unlabeled multiplication-stimulating activity. Specific multiplication-stimulating activity receptors also were demonstrated with which insulin did not interact even at 10 μg/ml. Half-maximal displacement of tracer multiplication-stimulating activity occured at 200 ng/ml unlabeled multiplication-stimulating activity. We conclude that insulin cannot act via the multiplication-stimulating activity receptor and presumably acts via typical insulin receptors. The effects of multiplication-stimulating activity on enzyme induction and amino acid transport are probably mediated primarily via the multiplication-stimulating activity receptor. 相似文献
242.
The association of cholesterol gall stones with coronary artery disease is controversial. To investigate this possible relation at the biochemical level, bile cholesterol saturation and the plasma concentrations of triglycerides, total cholesterol, and high-density-lipoprotein cholesterol (HDL cholesterol) were measured in 25 healthy, middle-aged women. Bile cholesterol saturation index was negatively correlated with HDL cholesterol. It was positively correlated with plasma triglycerides and with total cholesterol minus HDL cholesterol. These findings provide a biochemical basis for a positive association in women between cholesterol gall stones and coronary artery disease. 相似文献
243.
Summary Vitrification of plants in vitro is a physiological abnormality of tissue-cultured plants which causes significant losses in the micropropagation industry. Vitrified plants are waterlogged but the position of water within plants has not been identified. Nuclear magnetic resonance (NMR) imaging of normal tissue-cultured, vitrified tissue-cultured, and glasshouse-grown leaves ofGypsophila paniculata showed the distribution of water within the leaves. Normal tissue-cultured and glasshouse-grown leaves had a high concentration of water within leaf vascular bundles and lower concentrations elsewhere. In contrast, vitrified leaves had a relatively even distribution of high water concentration throughout the leaves. When imaging parameters were changed, so that only water associated with cell membranes was shown, the images of normal tissue-cultured and glasshouse-grown leaves did not change. However, the image of the vitrified leaves showed a general lowering of intensity across the whole of the leaf. The appearance of the NMR images, together with those obtained by light microscopy, suggest that the excess water associated with vitrified plants is located in the intercellular air spaces. The blockage of these spaces may lead to a cycle of perturbations in the plant's physiology culminating in the development of vitrification.Abbreviation NMR
nuclear magnetic resonance 相似文献
244.
Microorganisms found associated with commercially shelled pecan meats are numerous and varied. No bacteria and only two fungal microorganisms, Aspergillus clavatus and Tricothecium species, were found on aseptically shelled pecans. 相似文献
245.
Chris J. Curtis Chris D. Evans Christine L. Goodale Tim H.E. Heaton 《Ecosystems》2011,14(6):1021-1037
Various studies over the last 15 years have attempted to describe the processes of N retention, saturation and NO3
− leaching in semi-natural ecosystems based on stable isotope studies. Forest ecologists and terrestrial biogeochemists have
used 15N labelled NO3
− and NH4
+ tracers to determine the fate of atmospheric deposition inputs of N to terrestrial ecosystems, with NO3
− leaching to surface waters being a key output flux. Separate studies by aquatic ecologists have used similar isotope tracer
methods to determine the fate and impacts of inorganic N species, leached from terrestrial ecosystems, on aquatic ecosystems,
usually without reference to comparable terrestrial studies. A third group of isotopic studies has employed natural abundances
of 15N and 18O in precipitation and surface water NO3
− to determine the relative contributions of atmospheric and microbial sources. These three sets of results often appear to
conflict with one another. Here we attempt to synthesize and reconcile the results of these differing approaches to identifying
both the source and the fate of inorganic N in natural or semi-natural ecosystems, and identify future research priorities.
We conclude that the results of different studies conform to a consistent conceptual model comprising: (1) rapid microbial
turnover of atmospherically deposited NO3
− at multiple biologically active locations within both terrestrial and aquatic ecosystems; (2) maximum retention and accumulation
of N in carbon-rich ecosystems and (3) maximum leaching of NO3
−, most of which has been microbially cycled, from carbon-poor ecosystems exposed to elevated atmospheric N inputs. 相似文献
246.
Rahmioglu N Le Gall G Heaton J Kay KL Smith NW Colquhoun IJ Ahmadi KR Kemsley EK 《Journal of proteome research》2011,10(6):2807-2816
The activity of Cytochrome P450 3A4 (CYP3A4) enzyme is associated with many adverse or poor therapeutic responses to drugs. We used (1)H NMR-based metabonomics to identify a metabolic signature associated with variation in induced CYP3A4 activity. A total of 301 female twins, aged 45--84, participated in this study. Each volunteer was administered a potent inducer of CYP3A4 (St. John's Wort) for 14 days and the activity of CYP3A4 was quantified through the metabolism of the exogenously administered probe drug quinine sulfate (300 mg). Pre- and postintervention fasting urine samples were used to obtain metabolite profiles, using (1)H NMR spectroscopy, and were analyzed using UPLC--MS to obtain a marker for CYP3A4 induction, via the ratio of 3-hydroxyquinine to quinine (3OH-Q:Q). Multiple linear regression was used to build a predictive model for 3OH-Q:Q values based on the preintervention metabolite profiles. A combination of seven metabolites and seven covariates showed a strong (r = 0.62) relationship with log(3OH-Q:Q). This regression model demonstrated significant (p < 0.00001) predictive ability when applied to an independent validation set. Our results highlight the promise of metabonomics for predicting CYP3A4-mediated drug response. 相似文献
247.
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249.
250.
Engineering a root-specific, repressor-operator gene complex 总被引:1,自引:0,他引:1
Kim T Balish RS Heaton AC McKinney EC Dhankher OP Meagher RB 《Plant biotechnology journal》2005,3(6):571-582
Strong, tissue-specific and genetically regulated expression systems are essential tools in plant biotechnology. An expression system tool called a 'repressor-operator gene complex' (ROC) has diverse applications in plant biotechnology fields including phytoremediation, disease resistance, plant nutrition, food safety, and hybrid seed production. To test this concept, we assembled a root-specific ROC using a strategy that could be used to construct almost any gene expression pattern. When a modified E. coli lac repressor with a nuclear localization signal was expressed from a rubisco small subunit expression vector, S1pt::lacIn, LacIn protein was localized to the nuclei of leaf and stem cells, but not to root cells. A LacIn repressible Arabidopsis actin expression vector A2pot was assembled containing upstream bacterial lacO operator sequences, and it was tested for organ and tissue specificity using beta-glucuronidase (GUS) and mercuric ion reductase (merA) gene reporters. Strong GUS enzyme expression was restricted to root tissues of A2pot::GUS/S1pt::lacIn ROC plants, while GUS activity was high in all vegetative tissues of plants lacking the repressor. Repression of shoot GUS expression exceeded 99.9% with no evidence of root repression, among a large percentage of doubly transformed plants. Similarly, MerA was strongly expressed in the roots, but not the shoots of A2pot::merA/S1pt::lacIn plants, while MerA levels remained high in both shoots and roots of plants lacking repressor. Plants with MerA expression restricted to roots were approximately as tolerant to ionic mercury as plants constitutively expressing MerA in roots and shoots. The superiority of this ROC over the previously described root-specific tobacco RB7 promoter is demonstrated. 相似文献