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Parkson Lee-gau Chong - One of the best experts on this subject based on the ideXlab platform.
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Fluorescence studies of lipid Regular Distribution in membranes.
Chemistry and Physics of Lipids, 2002Co-Authors: Parkson Lee-gau Chong, Istvan P. SugarAbstract:This article reviews the use of fluorescent lipids and free probes in the studies of lipid Regular Distribution in model membranes. The first part of this article summarizes the evidence and physical properties for lipid Regular Distribution in pyrene-labeled phosphatidylcholine (PC)/unlabeled PC binary mixtures as revealed by the fluorescence of pyrene-labeled PC. The original and the extended hexagonal superlattice model are discussed. The second part focuses on the fluorescence studies of sterol Regular Distributions in membranes. The experimental evidence for sterol superlattice formation obtained from the fluorescent sterol (i.e. dehydroergosterol) and non-sterol fluorescent probes (e.g. DPH and Laurdan) are evaluated. Prospects and concerns are given with regard to the sterol Regular Distribution. The third part deals briefly with the evidence for polar headgroup superlattices. The emphasis of this article is placed on the new concept that membrane properties and activities, including the activities of surface acting enzymes, drug partitioning, and membrane free volume, are fine-tuned by minute changes in the concentration of bulky lipids (e.g. sterols and pyrene-containing acyl chains) in the vicinities of the critical mole fractions for superlattice formation.
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High Pressure Effects in Molecular Biophysics and Enzymology - Membrane-Free Volume Variation with Bulky Lipid Concentration by Regular Distribution: A Functionally Important Membrane Property Explored by Pressure Studies of Phosphatidylcholine Bilay
High Pressure Effects in Molecular Biophysics and Enzymology, 1996Co-Authors: Parkson Lee-gau ChongAbstract:We have used the dips in the ratio of excimer to monomer fluorescence intensity (E/M) as the index of lipid Regular Distribution to examine the effect of pressure on lipid lateral organization in the liquid-crystalline state of dimyristoylphosphatidylcholine (DMPC)/1-palmitoyl-2-(10-pyrenyl)decanoyl)-sn-glyceroI-3-phosphatidylcholine (Pyr-PC) bilayers. In the pressure range of 0.001-0.7 kbar at 30 °C, E/M dips remain discernible, suggesting that lipid Regular Distribution appears favorably in the liquid-crystalline state. In the same pressure range, E/M decreases steadily with increasing pressure at noncritical mole fractions; in contrast, E/M changes little with pressure at critical mole fractions. This result reveals an important physical principle underlying lipid Regular Distribution—that is, that membrane free volume reaches a local minimum at critical mole fractions of bulky lipids (for example, cholesterol and Pyr-PC). Using the activity of phospholipase A2 and the membrane fluidity inferred from diphenylhexatriene fluorescence polarization, we demonstrate that Regular Distribution of bulky lipids has a regulatory role in membrane properties or functions. Our data show that the activity of snake venom phospholipase A2 can be significantly modulated by minute changes (for example, 0.5 mol%) in the concentration of bulky lipids on either side of a critical mole fraction as a result of membrane free volume variation. The approach employed in this study illustrates the usefulness of high-pressure fluorescence methodology for obtaining new information about membranes at ambient conditions. High-pressure fluorescence spectroscopy has emerged as a powerful tool in biophysical research during the past 15 years (Paladini & Weber, 1981; Weber, 1992). Previous fluorescence studies of membranes at high pressure were focused on dynamic aspects, particularly on membrane fluidity. These dynamic studies have included probe rotations in lipid membranes (Chong & Weber, 1983; Chong et al., 1983; Mateo et al, 1993 and references cited therein), probe lateral diffusion (Flamm et al, 1982; Muller & Galla, 1983, 1987; Turley & Offen, 1985, 1986; Eisinger & Scarlata, 1987; Macdonald et al., 1988; Kao et al., 1992), spontaneous intermembrane transfer (Mantulin et al., 1984), and the relationship of membrane dynamics to the activity of membrane-bound proteins (Chong et al, 1985; Verjovski-Almeida et al, 1986; Jona & Martonosi, 1991).
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Fluorescence evidence for cholesterol Regular Distribution in phosphatidylcholine and in sphingomyeline lipid bilayers
Fluorescence Detection IV, 1996Co-Authors: Parkson Lee-gau Chong, Istvan P. Sugar, Fang Liu, Mei Mei Wang, Khanh Truong, Anthony A. Golsorkhi, Rhoderick E. BrownAbstract:Our previous studies indicated that sterols (including cholesterol and dehydroergosterol) can be Regularly distributed into hexagonal superlattices in the plane of liquid-crystalline phosphatidylcholine bilayers. It was suggested that Regular and irRegular regions coexist in the membrane. In the present study, we report supporting evidence for our sterol Regular Distribution model. We have examined the fractional concentration dependencies of dehydroergosterol (a naturally occurring cholesterol analog) fluorescence intensity and lifetime in various phosphatidylcholine and sphingomyelin bilayers. Fluorescence intensity and lifetime dips have been observed at specific sterol mole fractions. At those mole fractions, the acrylamide quenching rate constant of dehydroergosterol fluorescence reaches a local maximum. Those mole fractions match with the critical sterol mole fractions at which sterol molecules are expected to be Regularly distributed into hexagonal superlattices. The results support the idea that the sterols in the Regular region are embedded in the bilayer less deep than those in the irRegular regions. Furthermore, finding evidence for sterol Regular Distribution in both phosphatidylcholine and sphingomyelin membranes raises the possibility that sterol Regular Distribution may occur within phospholipid/cholesterol enriched domains of real biological membranes.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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Fluorescence evidence for cholesterol Regular Distribution in phosphatidylcholine and in sphingomyelin lipid bilayers.
Journal of fluorescence, 1996Co-Authors: Parkson Lee-gau Chong, Istvan P. Sugar, Fang Liu, Mei Mei Wang, Khanh Truong, Rhoderick E. BrownAbstract:Our previous studies indicated that sterols (including cholesterol and dehydroergosterol) can be Regularly distributed into hexagonal superlattices in the plane of liquid-crystalline phosphatidylcholine bilayers. It was suggested that Regular and irRegular regions coexist in the membrane. In the present study, we report supporting evidence for our sterol Regular Distribution model. We have examined the fractional concentration dependencies of dehydroergosterol (a naturally occurring cholesterol analogue) fluorescence intensity and lifetime in various phosphatidylcholine and sphingomyelin bilayers. Fluorescence intensity and lifetime dips have been observed at specific sterol mole fractions. At those mole fractions, the acrylamide quenching rate constant of dehydroergosterol fluorescence reaches a local maximum. Those mole fractions match the critical sterol mole fractions at which sterol molecules are expected to be Regularly distributed into hexagonal superlattices. The results support the idea that the sterols in the Regular region are embedded in the bilayer less deep than those in the irRegular regions. We have also examined the fractional cholesterol concentration dependencies of diphenylhexatriene (DPH) fluorescence intensity, lifetime, and polarization in DMPC vesicles. DPH fluorescence intensity and polarization also exhibit distinct dips and peaks, respectively, at critical sterol mole fractions for hexagonal superlattices. However, DPH lifetime changes little with sterol mole fraction. As a comparison, the fluorescence properties of DHE and DPH behave differently in response to the formation of sterol Regular Distribution. Furthermore, finding evidence for sterol Regular Distribution in both phosphatidylcholine and sphingomyelin membranes raises the possibility that sterol Regular Distribution may occur within phospholipid/cholesterol enriched domains of real biological membranes.
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Evidence for Regular Distribution of sterols in liquid crystalline phosphatidylcholine bilayers.
Proceedings of the National Academy of Sciences of the United States of America, 1994Co-Authors: Parkson Lee-gau ChongAbstract:Abstract To investigate the lateral organization of sterols in membranes, the fluorescence intensity of dehydroergosterol at different mole fractions in liquid crystalline dimyristoyl phosphatidylcholine bilayers was examined. A number of intensity drops were observed at specific mole fractions, as predicted from a hexagonal super-lattice model. The fluorescence dips provide compelling evidence that a naturally occurring sterol is Regularly distributed at fixed compositional fractions, consistent with the presence of hexagonal super-lattices in the fluid membranes. Regularly distributed regions, however, coexist with irRegularly distributed regions. The extent of Regular Distribution varies periodically with sterol mole fraction and, consequently, similar variations take place in the membrane volume and lipid packing. This level of modulation in local membrane structure by minute changes in sterol concentration should have profound implications for the functional role of cholesterol content in cell membranes.
Christian Ewerhart - One of the best experts on this subject based on the ideXlab platform.
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Regular type Distributions in mechanism design and $$\rho $$ -concavity
Economic Theory, 2013Co-Authors: Christian EwerhartAbstract:Some of the best-known results in mechanism design depend critically on Myerson’s (Math Oper Res 6:58–73, 1981 ) Regularity condition. For example, the second-price auction with reserve price is revenue maximizing only if the type Distribution is Regular. This paper offers two main findings. First, a new interpretation of Regularity is developed—similar to that of a monotone hazard rate—in terms of being the next to fail. Second, using expanded concepts of concavity, a tight sufficient condition is obtained for a density to define a Regular Distribution. New examples of Regular Distributions are identified. Applications are discussed.
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Regular type Distributions in mechanism design and \rho -concavity
Economic Theory, 2012Co-Authors: Christian EwerhartAbstract:Some of the best-known results in mechanism design depend critically on Myerson’s (Math Oper Res 6:58–73, 1981) Regularity condition. For example, the second-price auction with reserve price is revenue maximizing only if the type Distribution is Regular. This paper offers two main findings. First, a new interpretation of Regularity is developed—similar to that of a monotone hazard rate—in terms of being the next to fail. Second, using expanded concepts of concavity, a tight sufficient condition is obtained for a density to define a Regular Distribution. New examples of Regular Distributions are identified. Applications are discussed.
Istvan P. Sugar - One of the best experts on this subject based on the ideXlab platform.
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Fluorescence studies of lipid Regular Distribution in membranes.
Chemistry and Physics of Lipids, 2002Co-Authors: Parkson Lee-gau Chong, Istvan P. SugarAbstract:This article reviews the use of fluorescent lipids and free probes in the studies of lipid Regular Distribution in model membranes. The first part of this article summarizes the evidence and physical properties for lipid Regular Distribution in pyrene-labeled phosphatidylcholine (PC)/unlabeled PC binary mixtures as revealed by the fluorescence of pyrene-labeled PC. The original and the extended hexagonal superlattice model are discussed. The second part focuses on the fluorescence studies of sterol Regular Distributions in membranes. The experimental evidence for sterol superlattice formation obtained from the fluorescent sterol (i.e. dehydroergosterol) and non-sterol fluorescent probes (e.g. DPH and Laurdan) are evaluated. Prospects and concerns are given with regard to the sterol Regular Distribution. The third part deals briefly with the evidence for polar headgroup superlattices. The emphasis of this article is placed on the new concept that membrane properties and activities, including the activities of surface acting enzymes, drug partitioning, and membrane free volume, are fine-tuned by minute changes in the concentration of bulky lipids (e.g. sterols and pyrene-containing acyl chains) in the vicinities of the critical mole fractions for superlattice formation.
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Fluorescence evidence for cholesterol Regular Distribution in phosphatidylcholine and in sphingomyeline lipid bilayers
Fluorescence Detection IV, 1996Co-Authors: Parkson Lee-gau Chong, Istvan P. Sugar, Fang Liu, Mei Mei Wang, Khanh Truong, Anthony A. Golsorkhi, Rhoderick E. BrownAbstract:Our previous studies indicated that sterols (including cholesterol and dehydroergosterol) can be Regularly distributed into hexagonal superlattices in the plane of liquid-crystalline phosphatidylcholine bilayers. It was suggested that Regular and irRegular regions coexist in the membrane. In the present study, we report supporting evidence for our sterol Regular Distribution model. We have examined the fractional concentration dependencies of dehydroergosterol (a naturally occurring cholesterol analog) fluorescence intensity and lifetime in various phosphatidylcholine and sphingomyelin bilayers. Fluorescence intensity and lifetime dips have been observed at specific sterol mole fractions. At those mole fractions, the acrylamide quenching rate constant of dehydroergosterol fluorescence reaches a local maximum. Those mole fractions match with the critical sterol mole fractions at which sterol molecules are expected to be Regularly distributed into hexagonal superlattices. The results support the idea that the sterols in the Regular region are embedded in the bilayer less deep than those in the irRegular regions. Furthermore, finding evidence for sterol Regular Distribution in both phosphatidylcholine and sphingomyelin membranes raises the possibility that sterol Regular Distribution may occur within phospholipid/cholesterol enriched domains of real biological membranes.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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Fluorescence evidence for cholesterol Regular Distribution in phosphatidylcholine and in sphingomyelin lipid bilayers.
Journal of fluorescence, 1996Co-Authors: Parkson Lee-gau Chong, Istvan P. Sugar, Fang Liu, Mei Mei Wang, Khanh Truong, Rhoderick E. BrownAbstract:Our previous studies indicated that sterols (including cholesterol and dehydroergosterol) can be Regularly distributed into hexagonal superlattices in the plane of liquid-crystalline phosphatidylcholine bilayers. It was suggested that Regular and irRegular regions coexist in the membrane. In the present study, we report supporting evidence for our sterol Regular Distribution model. We have examined the fractional concentration dependencies of dehydroergosterol (a naturally occurring cholesterol analogue) fluorescence intensity and lifetime in various phosphatidylcholine and sphingomyelin bilayers. Fluorescence intensity and lifetime dips have been observed at specific sterol mole fractions. At those mole fractions, the acrylamide quenching rate constant of dehydroergosterol fluorescence reaches a local maximum. Those mole fractions match the critical sterol mole fractions at which sterol molecules are expected to be Regularly distributed into hexagonal superlattices. The results support the idea that the sterols in the Regular region are embedded in the bilayer less deep than those in the irRegular regions. We have also examined the fractional cholesterol concentration dependencies of diphenylhexatriene (DPH) fluorescence intensity, lifetime, and polarization in DMPC vesicles. DPH fluorescence intensity and polarization also exhibit distinct dips and peaks, respectively, at critical sterol mole fractions for hexagonal superlattices. However, DPH lifetime changes little with sterol mole fraction. As a comparison, the fluorescence properties of DHE and DPH behave differently in response to the formation of sterol Regular Distribution. Furthermore, finding evidence for sterol Regular Distribution in both phosphatidylcholine and sphingomyelin membranes raises the possibility that sterol Regular Distribution may occur within phospholipid/cholesterol enriched domains of real biological membranes.
Rhoderick E. Brown - One of the best experts on this subject based on the ideXlab platform.
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Fluorescence evidence for cholesterol Regular Distribution in phosphatidylcholine and in sphingomyeline lipid bilayers
Fluorescence Detection IV, 1996Co-Authors: Parkson Lee-gau Chong, Istvan P. Sugar, Fang Liu, Mei Mei Wang, Khanh Truong, Anthony A. Golsorkhi, Rhoderick E. BrownAbstract:Our previous studies indicated that sterols (including cholesterol and dehydroergosterol) can be Regularly distributed into hexagonal superlattices in the plane of liquid-crystalline phosphatidylcholine bilayers. It was suggested that Regular and irRegular regions coexist in the membrane. In the present study, we report supporting evidence for our sterol Regular Distribution model. We have examined the fractional concentration dependencies of dehydroergosterol (a naturally occurring cholesterol analog) fluorescence intensity and lifetime in various phosphatidylcholine and sphingomyelin bilayers. Fluorescence intensity and lifetime dips have been observed at specific sterol mole fractions. At those mole fractions, the acrylamide quenching rate constant of dehydroergosterol fluorescence reaches a local maximum. Those mole fractions match with the critical sterol mole fractions at which sterol molecules are expected to be Regularly distributed into hexagonal superlattices. The results support the idea that the sterols in the Regular region are embedded in the bilayer less deep than those in the irRegular regions. Furthermore, finding evidence for sterol Regular Distribution in both phosphatidylcholine and sphingomyelin membranes raises the possibility that sterol Regular Distribution may occur within phospholipid/cholesterol enriched domains of real biological membranes.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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Fluorescence evidence for cholesterol Regular Distribution in phosphatidylcholine and in sphingomyelin lipid bilayers.
Journal of fluorescence, 1996Co-Authors: Parkson Lee-gau Chong, Istvan P. Sugar, Fang Liu, Mei Mei Wang, Khanh Truong, Rhoderick E. BrownAbstract:Our previous studies indicated that sterols (including cholesterol and dehydroergosterol) can be Regularly distributed into hexagonal superlattices in the plane of liquid-crystalline phosphatidylcholine bilayers. It was suggested that Regular and irRegular regions coexist in the membrane. In the present study, we report supporting evidence for our sterol Regular Distribution model. We have examined the fractional concentration dependencies of dehydroergosterol (a naturally occurring cholesterol analogue) fluorescence intensity and lifetime in various phosphatidylcholine and sphingomyelin bilayers. Fluorescence intensity and lifetime dips have been observed at specific sterol mole fractions. At those mole fractions, the acrylamide quenching rate constant of dehydroergosterol fluorescence reaches a local maximum. Those mole fractions match the critical sterol mole fractions at which sterol molecules are expected to be Regularly distributed into hexagonal superlattices. The results support the idea that the sterols in the Regular region are embedded in the bilayer less deep than those in the irRegular regions. We have also examined the fractional cholesterol concentration dependencies of diphenylhexatriene (DPH) fluorescence intensity, lifetime, and polarization in DMPC vesicles. DPH fluorescence intensity and polarization also exhibit distinct dips and peaks, respectively, at critical sterol mole fractions for hexagonal superlattices. However, DPH lifetime changes little with sterol mole fraction. As a comparison, the fluorescence properties of DHE and DPH behave differently in response to the formation of sterol Regular Distribution. Furthermore, finding evidence for sterol Regular Distribution in both phosphatidylcholine and sphingomyelin membranes raises the possibility that sterol Regular Distribution may occur within phospholipid/cholesterol enriched domains of real biological membranes.
Hojatollah Zakerzadeh - One of the best experts on this subject based on the ideXlab platform.
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admissibility in non Regular family under squared log error loss
Metrika, 2015Co-Authors: Hojatollah Zakerzadeh, S Moradi H ZahraieAbstract:Consider an estimation problem under the squared-log error loss function in a one-parameter non-Regular Distribution when the endpoint of the support depends on an unknown parameter. The purpose of this paper is to give sufficient conditions for a generalized Bayes estimator of a parametric function to be admissible. Some examples are given. Copyright Springer-Verlag Berlin Heidelberg 2015
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Admissibility in non-Regular family under squared-log error loss
Metrika, 2015Co-Authors: Hojatollah Zakerzadeh, S. H. Moradi ZahraieAbstract:Consider an estimation problem under the squared-log error loss function in a one-parameter non-Regular Distribution when the endpoint of the support depends on an unknown parameter. The purpose of this paper is to give sufficient conditions for a generalized Bayes estimator of a parametric function to be admissible. Some examples are given.