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Anisotropy Measurements (anisotropy + measurement)
Kinds of Anisotropy Measurements Selected AbstractsGadolinium, a mechano-sensitive channel blocker, inhibits osmosis-initiated motility of sea- and freshwater fish sperm, but does not affect human or ascidian sperm motilityCYTOSKELETON, Issue 4 2003Zoltán Krasznai Abstract Exposure to hypo-osmotic or hyperosmotic environment triggers the initiation of fish sperm motility. In this article, we report that calcium and potassium channel blockers do not influence motility of puffer fish sperm but calmodulin antagonists reversibly decrease it, suggesting that calmodulin,Ca2+ interactions are prerequisite for the initiation of sperm motility in this species. Gadolinium (a stretch activated ion channel blocker) decreased the motility of puffer fish sperm from 92 ± 3% to 6 ± 3% and that of carp sperm from 91 ± 7% to 3.5 ± 4.3% in a dose-dependent manner (10,40 ,M). The effect of gadolinium was reversible, suggesting that stretch activated ion channels participate in the initiation of sperm motility of the two species. Gadolinium inhibits changes in the isoelectric point of certain proteins of puffer fish sperm, which occur when sperm motility is initiated in a hypertonic solution. Anisotropy measurements showed that hypo-osmotic treatment, which initiates carp sperm motility, increased membrane fluidity. When hypo-osmotic treatment was given in the presence of gadolinium, the sperm membrane remained as rigid as in quiescent cells, while motility was blocked. By contrast, gadolinium did not influence the motility parameters of Ciona or human sperm. Based on these lines of evidence, we suggest that conformational changes of mechanosensitive membrane proteins are involved in osmolality-dependent but not osmolality-independent sperm. Cell Motil. Cytoskeleton 55:232,243, 2003. © 2003 Wiley-Liss, Inc. [source] Synthesis and Photophysical Studies of a Pyrenylindole and a Phenalenoindole Obtained from Dehydroamino Acid Derivatives , Application as Fluorescent Probes for Biological SystemsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2009Goreti Pereira Abstract Two pyrenyl-dehydroamino acid derivatives were cyclized by a metal-assisted C,N intramolecular cyclization developed in our research group, to give a pyrenylindole and a phenalenoindole. The pyrenylindole was inserted into a peptide by solid-phase coupling, with use of a 2-chlorotrityl chloride resin and a Fmoc strategy. The photophysical properties of the pyrenylindole and phenalenoindole in several solvents were studied and showed that these compounds can be used as fluorescence probes. The results obtained with the peptide labelled with the pyrenylindole moiety show potential for use of this compound as a fluorescence label avoiding the aggregation propensity of pyrene compounds. Photophysical studies of the pyrenylindole and of the phenalenoindole in lipid membranes were also carried out. Steady-state fluorescence anisotropy measurements revealed that both compounds adopt locations inside the lipid bilayers and are able to report the transition between the gel and liquid-crystalline phases. The results point to potential use of these compounds as fluorescent probes for biological systems.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Paramagnetic and ferromagnetic anisotropy of magnetic susceptibility in migmatites: measurements in high and low fields and kinematic implicationsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004Eric C. Ferré SUMMARY The separation of paramagnetic and ferromagnetic anisotropy of magnetic susceptibility (AMS) is achieved in this study by using a vibrating sample magnetometer and a torque magnetometer performing directional anisotropy measurements in sufficiently high fields to saturate the ferromagnetic phases. The studied material, a migmatite from Minnesota, has a magnetic mineralogy characterized by ferrimagnetic multidomain titanomagnetite, paramagnetic biotite and a diamagnetic quartzo-feldspathic matrix. The low-field AMS represents the sum of ferromagnetic and paramagnetic contributions because the quartz contribution can be neglected, its magnetic susceptibility being two orders of magnitude smaller than that of biotite. In contrast, measurements in a high field isolate the paramagnetic component of the magnetic fabric. The high-field AMS is consistent between specimens and correlates well with measurements done using the torque magnetometer. The magnetic fabrics of the ferromagnetic and of the paramagnetic minerals are not co-axial, i.e. the subfabrics of the biotite and the magnetite are distinct. We propose that this non-coaxiality is due to a vorticity component during regional deformation and that it reflects the general conditions of deep crustal orogenic deformation. [source] Geomechanical simulation to predict open subsurface fracturesGEOPHYSICAL PROSPECTING, Issue 2 2009Helen Lewis ABSTRACT Geomechanical simulation of the evolution of a geological structure can play an important role in predicting open fracture development for all stages in that structure's development. In this work, three such geomechanical simulations are used to predict the evolving stress and strain fields, including dilational and compactional changes in the rock fabric in developing fault and fold systems. Their consequences for open fracture development and flow are addressed. These simulated stress and strain fields show considerable spatial and temporal heterogeneity that is consistent with deformation patterns observed in both natural examples and in laboratory-deformed analogues. But the stress and strain states that develop are neither co-axial nor do they bear a simple relationship to one another. The dilational and compactional strains, manifest as open fracturing or sealing, represent some significantly increased or significantly decreased flow rates. However, open-fracture predictions based on such geomechanical simulations are extremely difficult to validate with any degree of confidence as there is little direct evidence of sub-surface fracture distributions. In this context we also discuss possible integration of seismic anisotropy measurements, as an independent measure of open fracture alignment, to support the geomechanically derived fracture predictions. The focus of this work is on volumetric strains in fault zone evolution, though folding is also addressed. [source] RPA repair recognition of DNA containing pyrimidines bearing bulky adducts,JOURNAL OF MOLECULAR RECOGNITION, Issue 3 2008Irina O. Petruseva Abstract Recognition of new DNA nucleotide excision repair (NER) substrate analogs, 48-mer ddsDNA (damaged double-stranded DNA), by human replication protein A (hRPA) has been analyzed using fluorescence spectroscopy and photoaffinity modification. The aim of the present work was to find quantitative characteristics of RPA,ddsDNA interaction and RPA subunits role in this process. The designed DNA structures bear bulky substituted pyrimidine nitrogen bases at the inner positions of duplex forming DNA chains. The photoreactive 4-azido-2,5-difluoro-3- pyridin-6-yl (FAP) and fluorescent antracenyl, pyrenyl (Antr, Pyr) groups were introduced via different linker fragments into exo-4N of deoxycytidine or 5C of deoxyuridine. J-dU-containing DNA was used as a photoactive model of undamaged DNA strands. The reporter group was a fluorescein residue, introduced into the 5,-phosphate end of one duplex-forming DNA strand. RPA,dsDNA association constants and the molar RPA/dsDNA ratio have been calculated based on fluorescence anisotropy measurements under conditions of a 1:1 RPA/dsDNA molar ratio in complexes. The evident preference for RPA binding to ddsDNA over undamaged dsDNA distinctly depends on the adduct type and varies in the following way: undamaged dsDNA,<,Antr-dC-ddsDNA,<,mmdsDNA,<,FAPdU-, Pyr-dU-ddsDNA,<,FAP-dC-ddsDNA (KD,=,68,±,1; 25,±,6; 13,±,1; 8,±,2, and 3.5,±,0.5,nM correspondingly) but weakly depends on the chain integrity. Interestingly the bulkier lesions not in all cases have a greater effect on RPA affinity to ddsDNA. The experiments on photoaffinity modification demonstrated only p70 of compactly arranged RPA directly interacting with dsDNA. The formation of RPA,ddsDNA covalent adducts was drastically reduced when both strands of DNA duplex contained virtually opposite located FAP-dC and Antr-dC. Thus RPA requires undamaged DNA strand presence for the effective interaction with dsDNA bearing bulky damages and demonstrates the early NER factors characteristic features underlying strand discrimination capacity and poor activity of the NER system toward double damaged DNA. Copyright © 2008 John Wiley & Sons, Ltd. [source] Methoxypolyethylene glycol- block -polycaprolactone diblock copolymers reduce P-glycoprotein efflux in the absence of a membrane fluidization effect while stimulating P-glycoprotein ATPase activityJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2007Jason Zastre Abstract We have previously shown that amphiphilic diblock copolymers composed of methoxypolyethylene glycol- b -polycaprolactone (MePEG- b -PCL) increased the cellular accumulation and reduced the basolateral to apical flux of the P-glycoprotein substrate, rhodamine 123 (R-123) in caco-2 cells. The purpose of this study was to investigate membrane perturbation effects of MePEG- b -PCL diblock copolymers with erythrocyte membranes and caco-2 cells and the effect on P-gp ATPase activity. The diblock copolymer MePEG17 -b-PCL5 induced increasing erythrocyte hemolysis at concentrations which correlated with increasing accumulation of R-123 into caco-2 cells. However, no increase in cellular accumulation of R-123 by non-P-gp expressing cells was observed, suggesting that diblock did not enhance the transmembrane passive diffusion of R-123, but that the accumulation enhancement effect of the diblock in caco-2 cells was likely mediated primarily via P-gp inhibition. Fluorescence anisotropy measurements of membrane fluidity and P-gp ATPase activity demonstrated that MePEG17 - b -PCL5 decreased caco-2 membrane fluidity while stimulating ATPase activity approximately threefold at concentrations that maximally enhanced R-123 caco-2 accumulation. These results suggest that inhibition of P-gp efflux by MePEG17 - b -PCL5 does not appear to be related to increases in membrane fluidity or through inhibition in P-gp ATPase activities, which are two commonly reported cellular effects for P-gp inhibition mediated by surfactants. © 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 864,875, 2007 [source] Fluorescence resonance energy transfer and anisotropy reveals both hetero- and homo-energy transfer in the pleckstrin homology-domain and the parathyroid hormone-receptorMICROSCOPY RESEARCH AND TECHNIQUE, Issue 1 2009Ralf Steinmeyer Abstract We present a method and an apparatus of polarized fluorescence resonance energy transfer (FRET) and anisotropy imaging microscopy done in parallel for improved interpretation of the photophysical interactions. We demonstrate this apparatus to better determine the protein,protein interactions in the pleckstrin homology domain and the conformational changes in the Parathyroid Hormone Receptor, a G-protein coupled receptor, both fused to the cyan and yellow fluorescent proteins for either inter- or intramolecular FRET. In both cases, the expression levels of proteins and also background autofluorescence played a significant role in the depolarization values measured in association with FRET. The system has the sensitivity and low-noise capability of single-fluorophore detection. Using counting procedures from single-molecule methods, control experiments were performed to determine number densities of green fluorescence protein variants CFP and YFP where homo resonance energy transfer can occur. Depolarization values were also determined for flavins, a common molecule of cellular background autofluorescence. From the anisotropy measurements of donor and acceptor, the latter when directly excited or when excited by energy transfer, we find that our instrumentation and method also characterizes crucial effects from homotransfer, polarization specific photobleaching and background molecules. Microsc. Res. Tech., 2009. © 2008 Wiley-Liss, Inc. [source] Real-time monitoring of fluorescence anisotropy and temperature during processing of biaxially stretched polypropylene film,POLYMER ENGINEERING & SCIENCE, Issue 4 2004Anthony J. Bur An optical sensor based on fiber optics has been developed to measure fluorescence anisotropy and temperature during processing of biaxially stretched polypropylene films. The sensor, containing optical fibers, polarizing elements and lenses, was mounted above the polypropylene film as it was processed in a tenter frame oven stretching machine. Fluorescence observations were made using the fluorescent dye, bis (di-tert butylphenyl) perylenedicarboximide (BTBP), which was doped into the resin at very low concentrations. To monitor biaxial stretching, fluorescence anisotropy measurements were carried out with light polarized in the machine and the transverse directions corresponding to the directions of biaxial stretching. Fluorescence based temperature measurements were obtained from the ratio of fluorescence intensities at 544 nm and 577 nm. A matrix of experiments involving three levels of stretch ratio in both the machine and transverse directions was undertaken. We observed significant differences between anisotropy in the machine and transverse directions that we attributed to the sequential stretching operation, i.e., the film was stretched in the machine direction first, followed by stretching in the transverse direction, and to film temperature and strain rate for each stretching operation. The result was uniformly higher anisotropies in the machine direction. Film temperature obtained from fluorescence corresponded to oven thermocouple measurements within 2°C. Polym. Eng. Sci. 44:805,813, 2004. © 2004 Society of Plastics Engineers. [source] Photocontrollable Peptide-Based Switches Target the Anti-Apoptotic Protein Bcl-xLCHEMBIOCHEM, Issue 18 2008Sabine Kneissl Abstract Photocontrol of Bcl-xL binding affinity has been achieved by using short BH3 domain peptides for Bak72,87 and Bid91,111 alkylated with an azobenzene crosslinker through two cysteine residues with different sequence spacings. The power to control the conformation of the crosslinker and hence peptide structure was demonstrated by CD and UV/Vis spectroscopy. The binding affinity of the alkylated peptides with Bcl-xL was determined in their dark-adapted and irradiated states by fluorescence anisotropy measurements, and use of different cysteine spacings allowed either activation or deactivation of the binding activities of these peptide-based switches by application of light pulses. Helix-stabilized peptides exhibited high Bcl-xL binding affinity with dissociation constants of 42±9, 21±1, and 55±4 nM for Bak, Bak, and Bid, respectively (superscript numbers refer to the spacing between cysteine residues), and up to 20-fold enhancements in affinity in relation to their helix-destabilized forms. Bak, Bak, and Bid each displayed more than 200-fold selectivity for binding to Bcl-xL over Hdm2, which is targeted by the N-terminal helix of the tumor suppressor p53. Structural studies by NMR spectroscopy demonstrated that the peptides bind to the same cleft in Bcl-xL as the wild-type peptide regardless of their structure. This work opens the possibility of using such photocontrollable peptide-based switches to interfere reversibly and specifically with biomacromolecular interactions to study and modulate cellular function. [source] A Sensitive Fluorescence Anisotropy Method for Point Mutation Detection by Using Core,Shell Fluorescent Nanoparticles and High-Fidelity DNA LigaseCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2007Ting Deng Dr. Abstract The present study reports a proof-of-principle for a sensitive genotyping assay approach that can detect single nucleotide polymorphisms (SNPs) based on fluorescence anisotropy measurements through a core,shell fluorescent nanoparticles assembly and ligase reaction. By incorporating the core,shell fluorescent nanoparticles into fluorescence anisotropy measurements, this assay provided a convenient and sensitive detection assay that enabled straightforward single-base discrimination without the need of complicated operational steps. The assay was implemented via two steps: first, the hybridization reaction that allowed two nanoparticle-tagged probes to hybridize with the target DNA strand and the ligase reaction that generated the ligation between perfectly matched probes while no ligation occurred between mismatched ones were implemented synchronously in the same solution. Then, a thermal treatment at a relatively high temperature discriminated the ligation of probes. When the reaction mixture was heated to denature the duplex formed, the fluorescence anisotropy value of the perfect-match solution does not revert to the initial value, while that of the mismatch again comes back as the assembled fluorescent nanoparticles dispart. The present approach has been demonstrated with the discrimination of a single base mutation in codon 12 of a K-ras oncogene that is of significant value for colorectal cancers diagnosis, and the wild type and mutant type were successfully scored. Due to its ease of operation and high sensitivity, it was expected that the proposed detection approach might hold great promise in practical clinical diagnosis. [source] | |||||||||||||