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At least 721 records · Page 40Linked to original sources
PubMed2005

Determination of protein-ligand binding affinity by NMR: observations from serum albumin model systems.

The usefulness of bovine serum albumin (BSA) as a model protein for testing NMR methods for the study of protein-ligand interactions is discussed. Isothermal titration calorimetry established the binding affinity and stoichiometry of the specific binding site for L-tryptophan, D-tryptophan, naproxen, ibuprofen, salicylic acid and warfarin. The binding affinities of the same ligands determined by NMR methods are universally weaker (larger KD). This is because the NMR methods are susceptible to interference from additional non-specific binding. The L-tryptophan-BSA and naproxen-BSA systems were the best behaved model systems.

Animals↗
PubMed1998

Quantitative immunohistochemistry of androgen receptors in a microsphere model system and in prostate tissue sections.

OBJECTIVE: To evaluate androgen receptor (AR) levels to predict endocrine therapy response and prognosis. STUDY DESIGN: A sepharose microsphere model was employed to establish the relationship between level of immunohistochemical staining density and both antigen and primary antibody (F39.4.1) concentration. Subsequently, the results of the model system were compared with the results in routine prostate sections. RESULTS: A log-linear relationship was observed between optical density (OD) and primary antibody dilution measured in immunostained, antigen-coated microspheres with moderate antigen density. Similar titration curves were observed in prostate sections at the same dilution range, indicating that the microsphere model can be extrapolated to routine tissue sections. With microspheres with high coating density, the loglinear range of dilutions shifted to higher dilutions. CONCLUSION: Differences in AR levels in prostate tissue sections might be more accurately detected by comparison of titration curves of primary antibody than by comparison of OD values at a fixed primary antibody dilution.

Antibodies, Monoclonal↗
PubMed1991

Oxidation of tris to one-carbon compounds in a radical-producing model system, in microsomes, in hepatocytes and in rats.

The buffer substance tris(hydroxymethyl)aminomethane (Tris) is converted to formaldehyde in an hydroxyl radical producing model system and in rat liver microsomes, and to CO2 in rat hepatocytes and in the intact rat. In microsomes, formaldehyde formation from Tris is inhibited by catalase, by the antioxidant propylgallate and by the iron chelator deferoxamine, formaldehyde formation is stimulated by the addition of Fe (II) EDTA. In hepatocytes, the formation of [14C] CO2 from [14C] Tris is inhibited by propylgallate and by the iron chelator o-phenanthroline and is stimulated by the presence of a xanthine oxidase system plus Fe (II) EDTA in the medium. In the intact rat, the administration of [14C] Tris results in the exhalation of [14C] CO2. The results indicate that an oxidant formed via a Fenton-type reaction, possibly the hydroxyl radical, may be involved in the formation of one-carbon compounds from Tris.

Animals↗
PubMed1984

Measuring utilization and impact of home care services: a systems model approach for cost effectiveness.

The relevance of home care research to policy questions is discussed as framework for study on "effects" (precursors and sequelae) of home care. This study used a large, multi-service agency's longitudinal (8-year) case records (N = 2436) to examine a system model for relationships among entry characteristics, utilization of services, and need for services upon discharge from home care. Deducing case-mix from utilization patterns, pay plan at entry was identified as best of the available predictors of both duration and intensity (using multivariate analysis). Duration and intensity, dual contributors to "total visits," were found to vary inversely and were predicted by different entering pay plans. While 1/3 of all cases were discharged to informal or self care, that was the most prevalent exit status of the clients (49%) who entered directly from hospital care. The methods used in disaggregating and analyzing these retrospectively-coded case records suggest that home services research: 1. distinguish type, intensity, and duration as components of "total visits" which combine to account for costs of care; 2. find concomitants of functional level (such as pay plan) which are accessible for designating case mix for purpose of projecting service use; 3. measure effectiveness in terms relevant to stated objectives of the long term care system, which need to acknowledge mortality and to separate service needs at entry room those at exist from the series of formal and informal providers on a continuum of care.

Aged↗
PubMed1985

Reactions of proteins with oxidizing lipids. 1. Analytical measurements of lipid oxidation and of amino acid losses in a whey protein-methyl linolenate model system.

The reactions between protein-bound amino acids and oxidizing lipid were investigated in a whey protein-methyl linolenate (C18:3)-water model system. The extent of fat oxidation was followed by measuring oxygen uptake, hydroperoxide formation and hydrocarbon (ethane and pentane) formation. Significant losses occurred with lysine (up to 71%), tryptophan (up to 31%) and histidine (up to 57%). Methionine was extensively oxidized to its sulphoxide but less than 2% was further oxidized to the sulphone. No other amino acids were affected. Increasing storage temperature (20 degrees, 37 degrees, 55 degrees) resulted in an enhancement of fat oxidation reactions and amino acid degradation. Increasing water activity (0.28, 0.65, 0.90) increased losses of lysine and tryptophan but had no influence on the oxidation of methionine, the level of remaining hydroperoxides or O2 uptake. Hydrocarbons were decreased. Limitation of O2 uptake to 1 mol/mol lipid instead of excess O2 (O2 uptake about 2.5 mol/mol lipid in 4 weeks) significantly reduced the degradation of lysine and tryptophan but had less influence on the oxidation of methionine. The level of remaining hydroperoxides was increased but hydrocarbons were unaffected.

Amino Acids↗
PubMed2006

Green fluorescent protein-expressing Escherichia coli as a model system for investigating the antimicrobial activities of silver nanoparticles.

Recombinant Escherichia coli (E. coli) bacteria expressing green fluorescent protein (GFP) was used as a model system to investigate the antimicrobial activities of Ag nanoparticles (NPs). A convenient in situ method of Ag NP synthesis using sodium borohydride, in the bacterial growth medium, was developed to produce preformed NPs for the study. Fluorescence spectroscopic and microscopic techniques allowed rapid detection of time-dependent changes in bacterial growth as well as fluorescence characteristics in the presence of Ag NPs. In addition, X-ray diffraction, UV-vis spectroscopic, and transmission electron microscopic measurements were carried out to understand the effect of Ag NPs on the bacteria. Our observations indicated that Ag NPs, above a certain concentration, not only were bactericidal but also were found to reduce the sizes of treated bacteria in comparison to untreated ones. Cell lysis of Ag NP-treated bacteria was suggested by the increased GFP fluorescence obtained in the medium. In vitro DNA-Ag NP interaction was detected by spectrophotometric analysis. However, electrophoresis studies indicated no direct effect of Ag NPs on DNA or protein profiles.

Anti-Bacterial Agents↗
PubMed1975

Study of the mechanism of thyroid hormone secretion in an in vitro model system: indirect evidence for fusion of lysosomes with thyroglobulin liposomes.

The interaction between [131I]-thyroglobulin liposomes and thyroidal lysosomes was used as an in vitro model system for analyzing the relation of colloid droplets to lysosomes in follicular cells. The rates of hydrolysis of [131I]-thyroglobulin in a liposome-lysosome system (Lipo-Lyso system) and a thyroglobulin-lysosome system (TG-Lyso system) were compared. Hydrolysis of thyroglobulin in the Lipo-Lyso system increased hyperbolically and was greater than that in the TG-Lyso system for about 10 h. Liposomal thyroglobulin was not degraded by the 20,000 X g supernatant obtained on disruption of the lysosomal fraction. On varying the pH of the incubation medium, the highest activity was observed under acidic conditions in both systems. Under neutral or weakly alkaline conditions, the Lipo-Lyso system still showed 50% of the maximal hydrolytic activity, while the TG-Lyso system showed no activity. ATP and anaerobic conditions had no effect on either system. Cysteine (5 X 10-2M) and p-chloromercuribenzene sulfonic acid (PCMBS, 10-3 M) had not influence on hydrolysis in the Lipo-Lyso system, but in the TG-Lyso system cysteine greatly increased, and PCMBS significantly reduced the rate of hydrolysis. Dibutyryl cyclic AMP had no effect. Chlorpromazine (Cpz) decreased liposomal thyroglobulin hydrolysis in a concentration-dependent manner. In the TG-Lyso system, concentrations of 10-4M Cpz had no effect. These results strongly suggest that liposomes rapidly fused with lysosomes, providing optimal conditions for hydrolysis of thyroglobulin.

Adenosine Triphosphate↗
PubMed1990

Model systems for learning pediatric flexible bronchoscopy.

Considerable practice is necessary to develop the skills essential to successful and safe performance of flexible bronchoscopy, especially in pediatric patients. We review a number of model systems, both mechanical and living, for learning and maturing bronchoscopic skills. For each of the animal models (canine, feline, leporine, and simian), the relevant anatomy and anesthetic techniques as well as the relative advantages and disadvantages of each model are discussed.

Anesthesia↗
PubMed1996

The yeast, Saccharomyces cerevisiae, as a model system for the study of human genetic disease.

Many human genes associated with disease have close homologs in yeast. Based on this homology, many human proteins have been studied using yeast expression systems. This paper will review research done in our laboratory using a yeast expression system to study the human protein galactose-1-phosphate uridylyltransferase, associated with galactosemia, as well as highlighting some of the advantages of this model system.

Galactosemias↗
PubMed2005

Dynamical systems model of entrainment due to coherent structures.

The lifetime of a turbulent shear flow is inversely related to the amount of surrounding fluid it entrains. A dynamical systems model of such a flow, dominated by coherent structures, was recently proposed [R. Govindarajan, Phys. Rev. Lett. 88, 134503 (2002)], where an axisymmetric heated jet was modelled by a pair of leap-frogging vortex rings. In the present paper we study the equivalent two-dimensional flow, namely, two pairs of corotating point vortices, of opposite sign. We prove that the system is nonintegrable for any finite separation between the pairs, and show that entrainment is a natural consequence of chaotic advection. The effect of core diffusion due to viscosity is studied, and it is shown that the entrainment rate is reduced with increasing viscosity, by a reduction in leap-frogging frequency.

Journal Article↗
PubMed1997

A Study of the Mechanism of Bleaching Cotton Using Peracids and Hydrogen Peroxide as Model Systems

The mechanism of bleaching cotton dyed with the reactive dye 5-(4,6-dichlorotriazinyl)aminofluorescein has been investigated using hydrogen peroxide as a model system. A general strategy for the study of the mechanism and kinetics of bleaching is presented followed by the relevant theory to enable a discriminatory assessment of the experimental data obtained. A brief extension to the industrially relevant class of peracid bleaches is given. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed2006

Pyridine-Ag20 cluster: a model system for studying surface-enhanced Raman scattering.

This work presents a detailed analysis of enhanced Raman scattering of the pyridine-Ag(20) model system using time-dependent density functional theory. A consistent treatment of both the chemical and electromagnetic enhancements (EM) is achieved by employing a recently developed approach based on a short-time approximation for the Raman cross section. A strong dependence of the absolute and relative intensities on the binding site and excitation wavelength is found. The analysis of the Raman scattering cross sections shows the importance of different contributions to the enhancements, including static chemical enhancements (factor of 10), charge-transfer enhancements (10(3)), and EM enhancements (10(5)). The largest enhancement found (10(5)-10(6)) is due to the EM mechanism, with a small contribution from the chemical interaction. This suggests that the enhanced Raman scattering due to atomic clusters is comparable to findings on single nanoparticles. A combination of information about the vibrational motion and the local chemical environment provides a simple picture of why certain normal modes are enhanced more than others.

Journal Article↗
PubMed1982

Transition metal-catalysed oxidation of 3,3'-diaminobenzidine [DAB] in a model system.

The oxidation of 3,3'-diaminobenzidine [DAB] by H2O2 catalysed by 4 transition metals, Cu++, Co++, Fe+++ and Mn++, was investigated spectrophotometrically in a model system. The velocity of the reactions was higher with higher concentrations of DAB, H2O2 and a metal as well as with higher temperature. Optimal pH found for reactions catalysed by different transition metals was pH = 7.0 for Cu++ and Co++, pH - 6.0 for Fe+++ and pH - 9.0 for Mn++. A rapid spontaneous DAB oxidation by H2O2 in the absence of any transition metal was observed at pH less than 5.0.

3,3'-Diaminobenzidine↗
PubMed1994

Kinetic study on the nitrosation of dibenzylamine in a model system.

A kinetic study of the formation of N-nitrosodibenzylamine (NDBzA), from the nitrosation of dibenzylamine (DBzA) by sodium nitrite, was performed in a model system under conditions (temperature, pH) that are similar to those encountered in the industrial production of hams processed in elastic rubber nettings. The nitrosation reaction was carried out in a KH2PO4 buffer (0.5 M) at pH 5.8 and at a temperature of 69 degrees C. Since DBzA is insoluble in an aqueous buffer system, a non-ionic surfactant, Tween 20, was used as a solubilizing agent. The nitrosation reaction exhibited first-order kinetics with respect to DBzA and second-order kinetics with respect to nitrite. The calculated rate constant was 4.7 +/- 0.5 M-2/min. The pH profile of NDBzA formation was also determined. The optimal pH of NDBzA formation, 3.12, was close to the pKa of nitrous acid (HNO2, pKa = 3.1).

Benzylamines↗
PubMed1992

Murine thymocytes with ability to inhibit Il-2 production: I. Genetic differences between mouse strains and characterization of the model system.

An experimental system has been established to understand the poor interleukin-2 (Il-2) production by activated thymocytes. This model system is further characterized here and studies were done on the possible mechanism(s) involved. Thymocytes activated by Concanavalin-A (Con-A), or through the CD3 complex of the T-cell receptor (TCR), inhibit 95-99% of the Il-2 production by spleen cells, while thymocytes stimulated by rIl-2 or lipopolysaccharides (LPS) do not. The mechanism of inhibition is not due to production of soluble factors, consumption of available interleukin-1 (Il-1) or Il-2, but is dependent on cell-to-cell contact. Although cellular contact is needed, cytotoxicity is not involved. Prostaglandin production is not required for the generation or exertion of the inhibitory activity. Protein and DNA synthesis are necessary for exertion of the suppressive effect. We also demonstrate a genetic difference between different mouse strains in the ability to generate the inhibitory thymocytes. Activated Balb/c thymocytes inhibit spleen cells' Il-2 production in a non-MHC-restricted manner. Our studies demonstrate a regulatory capacity of activated thymocytes in vitro. This ability of the postnatal cells could be of relevance for understanding the latter events in T-cell education in the thymus and the role of Il-2 during this process.

Animals↗
PubMed2006

An integrated numerical and physical modeling system for an enhanced in situ bioremediation process.

Groundwater contamination due to releases of petroleum products is a major environmental concern in many urban districts and industrial zones. Over the past years, a few studies were undertaken to address in situ bioremediation processes coupled with contaminant transport in two- or three-dimensional domains. However, they were concentrated on natural attenuation processes for petroleum contaminants or enhanced in situ bioremediation processes in laboratory columns. In this study, an integrated numerical and physical modeling system is developed for simulating an enhanced in situ biodegradation (EISB) process coupled with three-dimensional multiphase multicomponent flow and transport simulation in a multi-dimensional pilot-scale physical model. The designed pilot-scale physical model is effective in tackling natural attenuation and EISB processes for site remediation. The simulation results demonstrate that the developed system is effective in modeling the EISB process, and can thus be used for investigating the effects of various uncertainties.

Biodegradation, Environmental↗
PubMed2006

Structure of a beta-sheet model system in the gas phase: analysis of the fingerprint region up to 10 microm.

In this communication we report on the conformational analysis of side-chains in the beta-sheet model system (Ac-Phe-OMe)(2) by applying IR/R2PI (infrared/resonant 2-photon ionisation) spectroscopy in the fingerprint region up to 10 microm, where in order to get information in this spectral region an extension of our new high energy and narrow band-width nanosecond IR laser system is presented.

Amino Acids↗