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31.
US Rao 《Canadian Metallurgical Quarterly》1998,37(42):14981-14988
P-glycoprotein (Pgp) mediates drug transport utilizing the energy released from ATP hydrolysis. However, the mechanism by which Pgp couples these two reactions remains unclear. The present work is undertaken to describe kinetically the first step, which is the interdependence of nucleotide and drug binding to the Pgp by the use of vanadate. Preincubation of human Pgp expressed in Sf9 insect cells with vanadate in the presence of Mg2+, ATP, and verapamil resulted in nearly complete and stable inhibition of the drug-stimulated ATPase function. In contrast, the Pgp ATPase function was nearly unaffected when Mg2+, ATP, or verapamil was omitted. Inhibition was highly specific for divalent cations that support ATP hydrolysis, for nucleotides that serve as substrates of hydrolysis, and for those drugs/compounds that interact with the drug-binding/transport sites of the Pgp. Kinetic analysis indicated that vanadate inhibition was MgATP concentration-dependent with an apparent Ki value similar to the apparent Km, suggesting that MgATP was bound to a similar ATP-binding site in both the ATPase inhibition and activation reactions. In support of this conclusion, vanadate, in the presence of Mg2+ and verapamil, caused selective trapping of 8-azido [alpha-32P] ATP and covalent labeling of ATP-binding site in the Pgp. Differences were observed in the vanadate-induced inhibition of wild-type and Val185 mutant Pgp's with different drug/compounds. These results suggested that the affinity of the interacting drug/compound is a constant and influences the overall stability of the inhibited Pgp species. Possible implications of these observations for the coupling of ATP hydrolysis to drug transport are discussed. 相似文献
32.
The average American diet, which is high in protein and low in fruits and vegetables, generates a large amount of acid, mainly as sulfates and phosphates. The kidneys respond to this dietary acid challenge with net acid excretion, as well as ammonium and titratable acid excretion. Concurrently, the skeleton supplies buffer by active resorption of bone. Indeed, calciuria is directly related to net acid excretion. Different food proteins differ greatly in their potential acid load, and therefore in their acidogenic effect. A diet high in acid-ash proteins causes excessive calcium loss because of its acidogenic content. The addition of exogenous buffers, as chemical salts or as fruits and vegetables, to a high protein diet results in a less acid urine, a reduction in net acid excretion, reduced ammonium and titratable acid excretion, and decreased calciuria. Bone resorption may be halted, and bone accretion may actually occur. Alkali buffers, whether chemical salts or dietary fruits and vegetables high in potassium, reverse acid-induced obligatory urinary calcium loss. We conclude that excessive dietary protein from foods with high potential renal acid load adversely affects bone, unless buffered by the consumption of alkali-rich foods or supplements. 相似文献
33.
With each sensational new development, the real life race for American dominance over Japan in next-generation flat panel displays is looking progressively more like a rough draft of a techno-thriller (with the likelihood of getting even rougher). The real life drama that is unfolding is not only exciting, it often seems less believable than fiction. In this episode of “America On Display,” we'll try to sort through what some of the leading characters have been up to lately, who they're working with (or against), and what the U.S. government and various “cooperative” catalysts are contributing to the chain of chaotic events. 相似文献
34.
The diffusional permeability coefficients, PD, for tritiated water (3HHO) 14C-antipyrine (AP) and 14C-iodoantipyrine (IAP) in isolated calf pulmonary artery endothelial cells and dog erythrocytes are measured with the linear diffusion technique at 11.5, 15, 20 and 37 degrees C. The PD values for both cell populations follow the sequence 3HHO > IAP > AP at each of the temperatures. PD for water is higher in the erythrocyte compared to the endothelial cells. The differences in PD for AP and IAP in the erythrocytes and endothelial cells are not dramatic and are similar to the differences seen in comparing permeation of the same solute through bilayers of different composition. A comparison of the values of PD calculated for the endothelial cells with those for isolated capillaries and the structured endothelium in whole lungs validates the use of the isolated cells as models for the endothelial cells in situ. Incubation of the endothelial cells with cis-vaccenic acid or cholesterol produces a reduction in PD for water and antipyrine. These data are analyzed in terms of Stokesian and non-Stokesian diffusion. The interpretation which best accommodates the data is that the phospholipid area of the membrane, rather than the hydrocarbon core, provides the greatest resistance to permeation for these solutes. 相似文献
35.
36.
T Ikonen M Uusitalo E Taskinen A Korpela US Salminen RE Morris AL Harjula 《Canadian Metallurgical Quarterly》1998,17(10):945-953
The subcellular localization of the phosphatidylglycerol/phosphatidylinositol transfer protein (PG/PI-TP) of Aspergillus oryzae was investigated using Western blot analysis of the cell protein extracts, a cellular membrane fractionation technique, and transmission electron microscopy. The PG/PI-TP, as detected by Western blot analysis with a specific immune serum, was found to be mainly cytoplasmic and partly associated with intracellular membranes. A fractionation experiment was conducted after homogenization of the filamentous fungus mycelium. The endoplasmic reticulum, Golgi-like vesicles, and the plasma membrane were separated by isopycnic ultracentrifugation on a sucrose gradient, and our data revealed that the immunodetected PG/PI-TP was only associated with the Golgi-like apparatus. All these results were documented by electron microscopy and indicate here for the first time that there exists a specific phospholipid transfer protein in a filamentous fungus that is localized in the cytoplasm and associated with Golgi-like vesicles. 相似文献
37.
Lee WH Rhee CK Koo J Lee J Jang SP Choi SU Lee KW Bae HY Lee GJ Kim CK Hong SW Kwon Y Kim D Kim SH Hwang KS Kim HJ Ha HJ Lee SH Choi CJ Lee JH 《Nanoscale research letters》2011,6(1):258-11
Ethylene glycol (EG)-based zinc oxide (ZnO) nanofluids containing no surfactant have been manufactured by one-step pulsed wire evaporation (PWE) method. Round-robin tests on thermal conductivity measurements of three samples of EG-based ZnO nanofluids have been conducted by five participating labs, four using accurate measurement apparatuses developed in house and one using a commercial device. The results have been compared with several theoretical bounds on the effective thermal conductivity of heterogeneous systems. This study convincingly demonstrates that the large enhancements in the thermal conductivities of EG-based ZnO nanofluids tested are beyond the lower and upper bounds calculated using the models of the Maxwell and Nan et al. with and without the interfacial thermal resistance. 相似文献
38.
KF Wilson P Fortes US Singh M Ohno IW Mattaj RA Cerione 《Canadian Metallurgical Quarterly》1999,274(7):4166-4173
In an attempt to further understand how nuclear events (such as gene expression, nuclear import/export, and cell cycle checkpoint control) might be subject to regulation by extracellular stimuli, we sought to identify nuclear activities under growth factor control. Using a sensitive photoaffinity labeling assay that measured [alpha-32P]GTP incorporation into nuclear proteins, we identified the 20-kDa subunit of the nuclear cap-binding complex (CBC) as a protein whose binding activity is greatly enhanced by the extracellular stimulation of serum-arrested cells. The CBC represents a 20- and 80-kDa heterodimer (the subunits independently referred to as CBP20 and CBP80, respectively) that binds the 7-methylguanosine cap on RNAs transcribed by RNA polymerase II. This binding facilitates precursor messenger RNA splicing and export. We have demonstrated that the [alpha-32P]GTP incorporation into CBP20 was correlated with an increased ability of the CBC to bind capped RNA and have used the [alpha-32P]GTP photoaffinity assay to characterize the activation of the CBC in response to growth factors. We show that the CBC is activated by heregulin in HeLa cells and by nerve growth factor in PC12 cells as well as during the G1/S phase of the cell cycle and when cells are stressed with UV irradiation. Additionally, we show that cap-dependent splicing of precursor mRNA, a functional outcome of CBC activation, can be catalyzed by growth factor addition to serum-arrested cells. Taken together, these data identify the CBC as a nuclear target for growth factor-coupled signal transduction and suggest novel mechanisms by which growth factors can influence gene expression and cell growth. 相似文献
39.
US Pahlm BR Chaitman PM Rautaharju RH Selvester GS Wagner 《Canadian Metallurgical Quarterly》1998,81(7):809-815
It is clinically important to estimate the size of a myocardial infarction (MI) to predict patient prognosis, to determine the ability of a therapy to limit its size, and to evaluate its effect on left ventricular function. Various electrocardiographic methods have been used for these purposes but their accuracies have not been compared with each other using an identical reference population of anatomically measured infarcts. The capability of 4 electrocardiographic scoring methods (the Selvester score, the Minnesota code, the Novacode, and the Cardiac Infarction Injury Score) to estimate MI size was compared using anatomic MI size in a group of 100 deceased patients. All patients had a standard 12-lead electrocardiogram of sufficient quality to perform manual waveform measurements and without confounding factors such as ventricular hypertrophy, fascicular block, or bundle branch block. The location and size of the left ventricular infarction was measured postmortem using the anatomic method of Ideker et al. All methods' size estimates correlated best with anatomic MI size in the anterior location (r = 0.65 to 0.89). The Selvester score was superior in estimating the sizes of inferior (r = 0.70) and posterolateral (r = 0.74) infarcts. For multiple infarcts all methods performed poorly (r = 0.18 to 0.44). 相似文献
40.
To increase our knowledge of the role of peptide hormone stimulation in gap junction protein expression and adrenal cortical cell function, primary rat adrenal cortical cells were treated with adrenocorticotropin, and gap junction proteins were measured. Immunocytochemistry and western blot analysis were used to detect and characterize gap junction type and distribution. The gap junction protein, connexin 43 (alpha 1), was detected. Analysis of six connexin protein types did not reveal gap junction species other than alpha 1. Cells of the inner adrenal cortical zones, zonae fasciculata and reticularis, were demonstrated to have the highest number of gap junctions per cell in the adrenal gland. Adrenal cell cultures enriched for the two inner cortical adrenal zones were established and demonstrated also to express alpha 1 gap junction protein. Adrenocorticotropin (40 mUnits/ml) and dibutyryl cyclic adenosine monophosphate (1 mM) treatments increased alpha 1 gap junction protein levels and decreased cell proliferation rates in the cell cultures. The results are consistent with the hypothesis that gap junction expression can be regulated by adrenocorticotropin acting through the second messenger cyclic adenosine monophosphate. It can be suggested that gap junction expression in the adrenal gland may be under hormonal influence, and that gap junctions serve as passage for movement of molecules involved in control of cell proliferation. 相似文献