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At least 1,495 records · Page 83Linked to original sources
PubMed2006

Analysis of genotype x environment interaction effects for starch pasting viscosity characteristics in Indica rice.

Milled rice (Oryza sativa L.) is composed of approximately 90% starch. The properties of starch have considerable effects on cooked rice palatability and consumer acceptability. Starch pasting viscosity parameters serve as important indices in the estimation of eating, cooking, and processing qualities of rice. In the present study, four cytoplasmic male-sterile (CMS) lines and eight restorer (R) lines have been used in an incomplete diallel cross to analyze seed effects, cytoplasmic effects, maternal gene effects, and their genotype x environment (GE) effects on the following starch pasting viscosity parameters: breakdown (BD), consistency (CS), and setback (SB). The results demonstrated that the total main genetic variances (V(G)) accounted for over 64% of the total genetic variance (V(G) +V(GE)) for the three traits, indicating that these traits were mainly controlled by the main genetic effects in addition to the GE interaction effects. The estimated total narrow-sense heritability were 67.8%, 79.5%, and 79.5% for BD, CS, and SB, respectively. The general heritability (h(2)(G)) accounted for over 75% of the total heritability (h(2)(G) +h(2)(GE)), indicating that early selection would be effective for those traits and the selection efficiencies were relatively stable in different environments.

Cytoplasm↗
PubMed2001

Influence of viscosity and ionic strength on the reaction kinetics of aldosterone and androstendione and their specific antibodies.

This paper analyses the influence of viscosity and ionic strength on the kinetics and equilibrium of the reactions of (125)I labelled androstendione and aldosterone with their specific antibodies used in the radioactive immunoassay determination of such hormones. Bi-exponential and irreversible kinetics is found for androstendione, and single-exponential and reversible ones for aldosterone. The results of the viscosity analysis reflect clear negative influence on direct reaction rate. Ionic strength excerpts some influence but not in a significant way, which suggests that the variation resulting from the effect of the glycerol addition is not due to the influence of the dielectric constant of the solutions used. The apparent product of the electrical charges is 0.228 for aldosterone, and 0.230 and -0.230 for androstendione. Results show diffusive control for both cases.

Aldosterone↗
PubMedDate not supplied

Glycemic and insulinemic responses of nondiabetic healthy adult subjects to an experimental acid-induced viscosity complex incorporated into a glucose beverage.

OBJECTIVE: An acid-induced-viscosity (I-V) complex containing alginate, citrate, and insoluble calcium was incorporated into a glucose-based beverage. We hypothesized that the acid I-V beverage would become viscous in the stomach (due to the solubilization of calcium and its interaction with alginate and citrate) and would blunt glycemia. METHODS: Thirty subjects were used in a double-masked, placebo-controlled crossover study evaluating the acid I-V complex. The placebo was a glucose-based beverage that had a similar total dietary fiber level and initial viscosity (Control). After a 12-h overnight fast, serum glucose and insulin were monitored over a 3-h postprandial period. RESULTS: The postprandial mean peak incremental change from baseline in serum glucose tended (P < 0.06) to be lower for the acid I-V product. The net incremental area under the curve (AUC) for serum glucose was reduced 75% (P < 0.01) by the acid I-V product, which was due mainly to an increased undershoot. The mean peak incremental change from baseline in serum insulin was higher (P < 0.05) for the acid I-V product. Net incremental AUC for serum insulin did not differ (P > 0.20) between products. CONCLUSIONS: Results of this study suggested that the acid I-V complex may attenuate the postprandial glycemic response to a glucose challenge in healthy subjects.

Adult↗
PubMed2000

A remote query magnetostrictive viscosity sensor.

Magnetically soft, magnetostrictive metallic glass ribbons are used as in-situ remote query viscosity sensors. When immersed in a liquid, changes in the resonant frequency of the ribbon-like sensors are shown to correlate with the square root of the liquid viscosity and density product. An elastic wave model is presented that describes the sensor response as a function of the frictional forces acting upon the sensor surface.

Electricity↗
PubMed2001

Addition of hydrogen bond donating excipients to oil solution: effect on in vitro drug release rate and viscosity.

In oily vehicles containing different hydrogen bond donating excipients rates of transfer of the weak electrolytes naproxen and lidocaine from the oil phase to the aqueous medium were measured by using the rotating dialysis cell. A logarithmic linear correlation was established between the apparent partition coefficient, P(app), and the first-order rate constant related to attainment of equilibrium between the two phases, k(obs), which fitted well with results from former publications. Further, release data for the non-electrolyte testosterone were found to fit into this linear correlation. Apparent partition coefficients were determined between oil vehicles containing various amounts of hydrogen bond donating excipients and phosphate buffer, pH 6.00, revealing a rise in log P(app) with increasing concentration of excipient. Viscosity was measured for castor oil containing vehicles showing a linear relationship between percentage (v/v) castor oil and log viscosity (mPas) of the mixed vehicle.

Anesthetics, Local↗
PubMed2001

Disposable TSM-biosensor based on viscosity changes of the contacting medium.

The thickness shear mode (TSM)-sensor responds to changes of mechanical properties of the material contacting the surface of the sensor. One of the material properties is the viscosity of a liquid. Abiosensor based on the TSM-resonator for the detection of endotoxin has been developed. It exploits the viscosity-density change during the reaction of endotoxin with limulus amebocyte lysate (LAL). The effect of surface properties of the sensor has been investigated to achieve better output signals. It is shown that the sensor requires a hydrophilic surface to get a better coupling between the sensor and the LAL-endotoxin solution. The TSM biosensor is able to detect an endotoxin concentration as low as 100 fg/ml by using only 50-microl standard LAL solution. The disadvantages of reusable sensors, such as the contamination from previous measurement of endotoxin and the cost of the regeneration or reclining processes of the sensor, have been eliminated by using a cost effective disposable TSM-sensor.

Animals↗
PubMed1987

Viscosity dependence of ethidium-DNA intercalation kinetics.

The kinetics of ethidium intercalation into double-stranded poly[d(G-C)] were investigated by use of repetitive pressure-jump chemical relaxation at 20 degrees C in low ionic strength (0.1 M NaCl) aqueous buffers containing either glycerol or methanol. The viscosity of the various solvents differed by more than an order of magnitude while other physical properties (e.g., dielectric constant) remained approximately constant. The single-reciprocal kinetic relaxation time (tau -1) increases linearly with DNA concentration. The observed association rate constant is lower in all organic-aqueous mixtures than in water and is inversely proportional to the viscosity. These results provide evidence for an additional step in the intercalation mechanism which is identified as an obligatory DNA conformational change preceding ethidium intercalation. From the data presented, the equilibrium constant of this local conformational change is approximately 10(-3), i.e., greatly favoring the structure incapable of intercalation. The corresponding kinetics were not directly determined; however, in order to be consistent with all of the data the forward and/or reverse rate constants of the conformational change must be larger than the rate of the intercalation reaction. Thus, it is proposed that the rate of the conformational change back to the nonintercalating B-DNA structure is greater than approximately 500 s-1, implying a rate of opening greater than approximately 0.5 s-1, in agreement with other hydrogen exchange and NMR data. The observed overall rate constant for the dissociation of ethidium is inversely proportional to the solvent density, possibly reflecting a dependence on the solvent free volume. The overall volume change of intercalation is less negative in the organic-aqueous solvent mixtures than in water.

DNA↗
PubMed1982

Investigation of diffusion-limited rates of chymotrypsin reactions by viscosity variation.

The possibility that the rates of acylation of chymotrypsin by certain highly reactive substrates approach the diffusion-controlled limits was investigated by measuring the values of kcat/Km for three substrates as a function of increasing viscosity with sucrose and ficoll as the viscosogenic reagents. The values of Kcat/Km (pH 8.0, 25 degrees C) representing the acylation rate constants are the following: N-(methoxycarbonyl)-L-tryptophan p-nitrophenyl ester, 3.5 x 10(7) M-1 s-1; N-acetyl-L-tryptophan methyl ester, 8 x 10(5) M-1 s-1; N-acetyl-L-tryptophan p-nitroanilide, 300 M-1 s-1. The rate constants decrease significantly with increasing viscosity for the first compound, decrease slightly for the second, and are insensitive to this perturbation for the third. The p-nitroanilide results taken together with the observation that the high concentrations of sucrose or ficoll used produce insignificant changes in kcat for the ester substrates argue against a general nonspecific perturbation in the enzyme structure effected by these reagents. The values of the association rate constants calculated from these results are 9 x 10(7) and 1 x 10(7) M-1 s-1 for the p-nitrophenyl and methyl esters, respectively. The values of kcat/Km divided by the association rate constants show that the rates of acylation by the p-nitrophenyl ester occur at ca. 40% and by the methyl ester at ca. 10% of the diffusion limits. Possibilities involving reorientation of a nonproductively bound substrate within the ES complex or desolvation of part of the active site of the enzyme are considered to account for the lower association rate constant for the methyl as compared to the p-nitrophenyl ester.

Chemical Phenomena↗
PubMed2006

Probing the chemical steps of nitroalkane oxidation catalyzed by 2-nitropropane dioxygenase with solvent viscosity, pH, and substrate kinetic isotope effects.

Among the enzymes that catalyze the oxidative denitrification of nitroalkanes to carbonyl compounds, 2-nitropropane dioxygenase is the only one known to effectively utilize both the neutral and anionic (nitronate) forms of the substrate. A recent study has established that the catalytic pathway is common to both types of substrates, except for the initial removal of a proton from the carbon of the neutral substrates [Francis, K., Russell, B., and Gadda, G. (2005) J. Biol. Chem. 280, 5195-5204]. In the present study, the mechanistic properties of the enzyme have been investigated with solvent viscosity, pH, and kinetic isotope effects. With nitroethane or ethylnitronate, the kcat/Km and kcat values were independent of solvent viscosity, consistent with the substrate and product binding to the enzyme in rapid equilibrium. The abstraction of the proton from the alpha carbon of neutral substrates was investigated by measuring the pH dependence of the D(kcat/KNE) value with 1,1-[2H2]-nitroethane. The formation of the enzyme-bound flavosemiquinone formed during catalysis was examined by determining the pH dependence of the kcat/Km values with ethylnitronate and nitroethane and the inhibition by m-nitrobenzoate. Finally, alpha-secondary kinetic isotope effects with 1-[2H]-ethylnitronate were used to propose a non-oxidative tautomerization pathway, in which the enzyme catalyzes the interconversion of nitroalkanes between their anionic and neutral forms. The data presented suggest that enzymatic turnover of 2-nitropropane dioxygenase with neutral substrates is limited by the cleavage of the substrate CH bond at low pH, whereas that with anionic substrates is limited by the non-oxidative tautomerization of ethylnitroante to nitroethane at high pH.

Alkanes↗
PubMed1999

Catalytic cycle of the phosphatidylcholine-preferring phospholipase C from Bacillus cereus. Solvent viscosity, deuterium isotope effects, and proton inventory studies.

The phosphatidylcholine-preferring phospholipase C from Bacillus cereus (PLCBc) is a 28.5 kDa enzyme with three zinc ions in its active site. Although much is known about the roles that various PLCBc active site amino acids play in binding and catalysis, there is little information about the rate-determining step of the PLCBc-catalyzed hydrolysis of phospholipids and the catalytic cycle of the enzyme. To gain insight into these aspects of the hydrolysis, solvent viscosity variation experiments were conducted to determine whether an external step (substrate binding or product release) or an internal step (hydrolysis) is rate-limiting. The data indicate that the PLCBc-catalyzed reaction is unaffected by changes in solvent viscosity. This observation is inconsistent with the notion of substrate binding or product release being rate-determining and supports the hypothesis that a chemical step is rate-limiting. Furthermore, a deuterium isotope effect of 1.9 and a linear proton inventory plot indicate one proton is transferred in the rate-determining step. These data may be used to formulate a comprehensive catalytic cycle that is for the first time based on experimental evidence. In this mechanism, Asp55 of PLCBc activates an active site water molecule for attack on the phosphodiester bond, the hydrolysis of which is rate-limiting. The phosphorylcholine product is the first to leave the active site, followed by diacylglycerol.

Bacillus cereus↗
PubMedDate not supplied

Model-independent relationships between hematocrit, blood viscosity, and yield stress derived from Couette viscometry data.

This paper describes a procedure, based on Tikhonov regularization, for obtaining the shear rate function or equivalently the viscosity function of blood from Couette viscometry data. For data sets that include points where the sample in the annulus is partially sheared the yield stress of blood will also be obtained. For data sets that do not contain partially sheared points, provided the shear stress is sufficiently low, a different method of estimating the yield stress is proposed. Both the shear rate function and yield stress obtained in this investigation are independent of any rheological model of blood. This procedure is applied to a large set of Couette viscometer data taken from the literature. Results in the form of shear rate and viscosity functions and yield stress are presented for a wide range of hematocrits and are compared against those reported by the originators of the data and against independently measured shear properties of blood.

Blood Viscosity↗
PubMedDate not supplied

Solvent and viscosity effects on the rate-limiting product release step of glucoamylase during maltose hydrolysis.

Release of product from the active site is the rate-limiting step in a number of enzymatic reactions, including maltose hydrolysis by glucoamylase (GA). With GA, an enzymatic conformational change has been associated with the product release step. Solvent characteristics such as viscosity can strongly influence protein conformational changes. Here we show that the rate-limiting step of GA has a rather complex dependence on solvent characteristics. Seven different cosolvents were added to the GA/maltose reaction solution. Five of the cosolvents, all having an ethylene glycol base, resulted in an increase in activity at low concentration of cosolvent and variable decreases in activity at higher concentrations. The increase in enzyme activity was dependent on polymer length of the cosolvent; the longer the polymer, the lower the concentration needed. The maximum increase in catalytic activity at 45 degrees C (40-45%) was obtained with the three longest polymers (degree of polymerization from 200 to 8000). A further increase in activity to 60-65% was obtained at 60 degrees C. The linear relationship between ln(kcat) and (viscosity)2 obtained with all the cosolvents provides further evidence that product release is the rate-limiting step in the GA catalytic mechanism. A substantial increase in the turnover rate of GA by addition of relatively small amounts of a cosolvent has potential applications for the food industry where high-fructose corn syrup (HFCS) is one of the primary products produced with GA. Since maltodextrin hydrolysis by GA is by far the slowest step in the production of HFCS, increasing the catalytic rate of GA can substantially reduce the process time.

Binding Sites↗
PubMed2006

A brief review of the relationships between monolayer viscosity, phase behavior, surface pressure, and temperature using a simple monolayer viscometer.

The two-dimensional surface shear viscosity, eta, of fatty acid monolayers of different chain lengths, measured using a simple magnetic needle viscometer, strongly correlates with the molecular organization in condensed phases and the absolute temperature. eta can increase by orders of magnitude at phase boundaries associated with tilted to untilted molecular order, providing the underlying order is semicrystalline. Hence, untilted, long-range ordered CS phases are the most viscous films. However, despite being untilted, the LS rotator phase is less viscous than certain laterally ordered tilted phases, suggesting a decrease of the van der Waals interactions due to molecular rotation. In certain regions of the L2 phase, eta reaches a maximum before the L2-LS transition, an anomalous behavior correlated with the change in the lattice symmetry of the headgroup. Surface shear viscosity, even when measured with a macroscopic probe, is particularly sensitive to the microscopic organization of monolayers.

Fatty Acids↗
PubMed1999

Preparation of encapsulated proteins dissolved in low viscosity fluids.

The majority of proteins are too large to be comprehensively examined by solution NMR methods, primarily because they tumble too slowly in solution. One potential approach to making the NMR relaxation properties of large proteins amenable to modern solution NMR techniques is to encapsulate them in a reverse micelle which is dissolved in a low viscosity fluid. Unfortunately, promising low viscosity fluids such as the short chain alkanes, supercritical carbon dioxide, and various halocarbon refrigerants all require the application of significant pressure to be kept liquefied at room temperature. Here we describe the design and use of a simple cost effective NMR tube suitable for the preparation of solutions of proteins encapsulated in reverse micelles dissolved in such fluids.

Capsules↗
PubMed2003

Preparation, characterization, and NMR spectroscopy of encapsulated proteins dissolved in low viscosity fluids.

Encapsulating a protein in a reverse micelle and dissolving it in a low-viscosity solvent can lower the rotational correlation time of a protein and thereby provides a novel strategy for studying proteins in a variety of contexts. The preparation of the sample is a key element in this approach and is guided by a number of competing parameters. Here we examine the applicability of several strategies for the preparation and characterization of encapsulated proteins dissolved in low viscosity fluids that are suitable for high performance NMR spectroscopy. Ubiquitin is used as a model system to explore various issues such as the homogeneity of the encapsulation, characterization of the hydrodynamic performance of reverse micelles containing protein molecules, and the effective pH of the water environment of the reverse micelle.

Capsules↗
PubMed2003

Effects of a beverage containing an enzymatically induced-viscosity dietary fiber, with or without fructose, on the postprandial glycemic response to a high glycemic index food in humans.

OBJECTIVE: Dietary supplementation with guar gum or fructose has been reported to reduce the postprandial glycemic response to an oral glucose challenge. As a result of the poor palatability of most foods containing guar gum, a novel low-viscosity beverage with guar gum was developed that becomes viscous in vivo through an enzymatic induction. The primary study objective was to determine the effect of an amylase-induced viscosity (I-V) product, with or without supplemental fructose, on the postprandial glycemic response to a high glycemic index test meal in healthy nondiabetic subjects. DESIGN: The study was a four-treatment, placebo-controlled, double-blind, randomized block protocol. SETTING: The study was performed at Glycaemic Index Testing, Inc., Toronto, Ontario, Canada. SUBJECTS: A total of 30 healthy nondiabetic volunteers (13 male, 17 female, mean+/-s.e.m. age of 51+/-3 y and body mass index of 24.2+/-0.4 kg/m(2)) participated in the study. INTERVENTION: In the morning after an overnight fast, subjects participated in four 3-h meal glucose tolerance tests on separate occasions. The test meals contained 50 g of available carbohydrate from maltodextrin and white bread (control) or the same meal with either 5 g of guar gum (3.6 g galactomannan), 5 g of fructose, or 5 g of guar gum +5 g of fructose. RESULTS: Treatments containing guar gum had a reduced (P<0.01) baseline-adjusted peak glucose response and incremental area under the glucose curve. In contrast to previous studies, fructose increased (P<0.05) the baseline-adjusted peak glucose concentration. CONCLUSIONS: Guar gum incorporated into an amylase I-V product provided a means to stabilize blood glucose levels by reducing the early phase excursion and then by appropriately maintaining the later phase excursion in healthy nondiabetic humans.

Adolescent↗
PubMed1994

Elevated protein tyrosine phosphatase activity and increased membrane viscosity are associated with impaired activation of the insulin receptor kinase in old rats.

Insulin resistance is very common in the elderly, and may be associated with glucose intolerance or frank diabetes. In previous studies we demonstrated that insulin resistance in old Wistar rats is associated with decreased autophosphorylation and activation of the hepatic insulin receptor kinase (IRK) in vivo. We now show that this defect can be reproduced in vitro, where the extent of insulin-induced activation of IRK in liver membranes of old rats was decreased by approximately 50% compared with young controls. The defect could be largely abolished after solubilization of the membranes with Triton X-100. We also show that: (a) the viscosity of membranes from the old rats was significantly (P < 0.001, n = 4) higher (by 15%) compared with young controls; (b) incubation of plasma membranes from old animals with lecithin liposomes, which lowered their cholesterol levels, partially abolished the defect in IRK activation; and (c) Triton extracts of liver membranes prepared from old rats did not interfere with the activation of IRK derived from young controls. Additionally, non-membrane components did contribute to the development of this defect. We observed a significant (approximately 30%) (P < 0.001, n = 18) elevation of cytosolic protein tyrosine phosphatase (PTP) activity directed against the beta subunit of the insulin receptor in livers of old rats. No such elevation of PTP activity could be demonstrated with synthetic substrates. Our findings are consistent with a model in which increased membrane viscosity as well as enhancement of a cytosolic PTP activity both markedly inhibit the activation in vivo of the hepatic IRK in old animals.

Aging↗
PubMed2000

Which one of these is not like the others? An inter-hospital study of the viscosity of thickened fluids.

This investigation examined the rheological (viscosity and yield stress) and material property (density) characteristics of the thickened meal-time and videofluorscopy fluids provided by 10 major metropolitan hospitals. Differences in the thickness of thickened fluids were considered as a source of variability and potential hazard for inter-hospital transfers of dysphagic patients. The results indicated considerable differences in the viscosity, density, and yield stress of both meal-time and videofluoroscopy fluids. In theory, the results suggest that dysphagic patients transferred between hospitals could be placed on inappropriate levels of fluid thickness because of inherent differences in the rheology and material property characteristics of the fluids provided by different hospitals. Slowed improvement or medical complications are potential worst-case scenarios for dysphagic patients if the difference between the thick fluids offered by 2 hospitals are extreme. The investigation outlines the most appropriate way to assess the rheological and material property characteristics of thickened fluids. In addition, it suggests a plan of quality improvement to reduce the variability of the thickness of fluids offered at different hospitals.

Deglutition Disorders↗