Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In fluid monolayers approaching collapse, phospholipids and their complexes with diacylglycerols hinder adsorption to the monolayer of the amphipathic protein, colipase. Herein, a statistical, free-area model, analogous to that used to analyze two-dimensional lipid diffusion, is developed to describe regulation by lipids of the initial rate of protein adsorption from the bulk aqueous phase to the lipid-water interface. It is successfully applied to rate data for colipase adsorption to phospholipid alone and yields realistic values of the two model parameters; the phospholipid excluded area and the critical free surface area required to initiate adsorption. The model is further developed and applied to analyze colipase adsorption rates to mixed monolayers of phospholipid and phospholipid-diacylglycerol complexes. The results are consistent with complexes being stably associated over the physiologically relevant range of lipid packing densities and being randomly distributed with uncomplexed phospholipid molecules. Thus, complexes should form in fluid regions of cellular membranes at sites of diacylglycerol generation. If so, by analogy with the behavior of colipase, increasing diacylglycerol may not trigger translocation of some amphipathic peripheral proteins until its abundance locally exceeds its mole fraction in complexes with membrane phospholipids.
 ...
PMID:Peripheral protein adsorption to lipid-water interfaces: the free area theory. 1615 Sep 72

We have investigated the miscibility in the mixed monolayers of cholesterol (Ch)-octyl cyano biphenyl (8CB) and cholesteryl acetate (ChA)-8CB using surface manometry and epifluorescence microscopic techniques. The main skeleton is the same both in Ch and ChA, whereas the polar head group is alcohol in Ch and ester in ChA. The 8CB molecule has a polar cyano as a terminal group and we probe its interaction with the polar group of Ch or ChA molecules in the mixed monolayers. Both Ch-8CB and ChA-8CB mixed monolayers exhibit two collapse pressures. In the case of the Ch-8CB mixed monolayer, the lower collapse pressure varies after 0.6 mole fraction (MF) of Ch in 8CB and the higher collapse pressure is nearly independent of composition. In ChA-8CB mixed monolayer, the lower collapse pressure varies continuously with the composition of ChA while the higher collapse pressure is nearly independent of the composition of ChA. In both these mixed monolayers, above the lower collapse pressure, 8CB gets squeezed out of the monolayer and forms multilayers. We find that in the case of Ch-8CB there is a phase separation in the monolayer occurring in the range of 0.15-0.9 MF of Ch. However, in ChA-8CB, the monolayer phase is miscible in all the proportions (except at very high concentration of ChA) below the lower collapse pressure. We attribute this better miscibility in the ChA-8CB compared to the Ch-8CB to the role played by the ester and cyano polar head group interactions.
 ...
PMID:Polar head group interactions in mixed Langmuir monolayers. 1624 Dec 36

The mixing behavior of 1-(perfluorobutyl)undecanoic acid-pentadecanoic acid (C15), 1-(perfluorohexyl)undecanoic acid-heptadecanoic acid (C17), and 1-(perfluorooctyl) undecanoic acid-nonadecanoic acid (C19) mixtures was investigated at the air-water interface. The compression isotherms of the fluorocarbon acid-hydrocarbon acid mixtures were recorded at various compositions on hydrochloric acid (pH 1.9, 37+/-2 degrees C) as a subphase. The phase transition, limiting molecular area, area at collapse pressure, and collapse pressure were determined for all pi-A isotherms. The mixing behavior was assessed by analyzing the concentration dependence of the average molecular area at constant film pressure (area/mole fraction or A-X diagram) and the concentration dependence of the phase transition, where possible. All three acid mixtures show a negative deviation from ideal behavior at surface pressures between 5 and 20 mN/m, which is indicative of an attractive interaction of both compounds in the mixed monolayer at the air-water interface. The miscibility apparently decreases with increasing chain length of the carboxylic acids (C15>C17>C19).
 ...
PMID:Mixing of partially fluorinated carboxylic acids with their hydrocarbon analogs at the air-water interface. 1629 Jun 12

Surface pressure-area (pi-A), surface potential-area (DeltaV-A), and dipole moment-area (mu( perpendicular)-A) isotherms were obtained for the Langmuir monolayer of two fluorinated-hydrogenated hybrid amphiphiles (sodium phenyl 1-[(4-perfluorohexyl)-phenyl]-1-hexylphosphate (F6PH5PPhNa) and (sodium phenyl 1-[(4-perfluorooctyl)-phenyl]-1-hexylphosphate (F8PH5PPhNa)), DPPC and their two-component systems at the air/water interface. Monolayers spread on 0.02 M Tris buffer solution (pH 7.4) with 0.13M NaCl at 298.2K were investigated by the Wilhelmy method, ionizing electrode method and fluorescence microscopy. Moreover, the miscibility of two components was examined by plotting the variation of the molecular area and the surface potential as a function of the molar fraction for the fluorinated-hydrogenated hybrid amphiphiles on the basis of the additivity rule. The miscibility of the monolayers was also examined by construction of two-dimensional phase diagrams. Furthermore, assuming the regular surface mixture, the Joos equation for analysis of the collapse pressure of two-component monolayers allowed calculation of the interaction parameter (xi) and the interaction energy (-Deltaepsilon) between the fluorinated-hydrogenated hybrid amphiphiles and DPPC. The observations by a fluorescence microscopy also supported our interpretation as for the miscibility in the monolayer state. Comparing the monolayer behavior between the two binary systems, no remarkable difference was found among various aspects. Among the two combinations, the mole fraction dependence in monolayer properties was commonly classified into two ranges: 0 <or= X <or= 0.3 and 0.3 < X <or = 1. Dependence of the chain length of fluorinated part was reflected for the molecular packing and surface potential.
 ...
PMID:Langmuir monolayer properties of the fluorinated-hydrogenated hybrid amphiphiles with dipalmitoylphosphatidylcholine (DPPC). 1642 22

Long-chain cationic amphipaths are routinely used for transfecting DNA into cells, although the mechanism of DNA delivery by these agents is poorly understood. Since their interfacial properties are undoubtedly involved at some stage in the process, a comprehensive study of the surface behavior of at least one of these compounds is highly desirable. Hence, the behavior of the cationic transfection agent EDOPC (dioleoyl-sn-glycerol-3-ethylphosphocholine or O-ethyldioleoylphosphatidylcholine), has been characterized at the air-water interface, by itself and in mixtures with other phospholipids. Surface pressure-molecular area isotherms obtained at the argon-buffer interface revealed that EDOPC is considerably (5-10 A(2)) more expanded than the parent phosphatidylcholine (DOPC) and even more expanded than the corresponding phosphatidylglycerol (DOPG), which has a similar charge density (of opposite polarity) as EDOPC. A 1:1 mixture of EDOPC and DOPG is very slightly condensed relative to DOPG and considerably condensed relative to EDOPC. The surface/dipole potential of this mixture is the mean of those of EDOPC and DOPG and is almost the same as that of DOPC. When the composition of EDOPC mixtures was varied, several surface parameters, including surface dipole moment, collapse pressure, and compressibility, exhibited discontinuities at a 1:1 mole ratio. EDOPC is unusually surface-active; the equilibrium surface tension of its dispersion was lower and the rate of fall of the surface tension (dynamic surface activity) of a dispersion with an initially clean surface was more than an order of magnitude greater than that for dispersions of DOPG. A 1:1 mixture of the cationic lipoid and phosphatidylglycerol had lower surface activity than DOPC in water but similar surface activity in 0.1 NaCl. Analysis, in terms of surface concentration, of the formation of EDOPC monolayers at the air interface of vesicle dispersions revealed a simple exponential rise to a maximum, at least for higher concentrations. Addition of a small proportion of DNA to EDOPC increased its dynamic surface activity even though DNA alone has no detectable surface activity at the concentrations used. This enhancement by DNA is presumably due to the disruption of the continuity of the bilayer and creation of defects from which lipoid spreads readily. The surface properties of this cationic compound, both alone and in combination with anionic lipids, provide insight into the previously described nonbilayer phase preferences of cationic-anionic lipid mixtures. In addition, they provide critical data (area condensation of mixed cationic-anionic monolayers) supporting a previously proposed mechanism of fusion of cationic bilayers with anionic bilayers. Such a process, involving anionic cellular membranes, is believed to be required for release of DNA from lipoplexes and is therefore a key stage of transfection.
 ...
PMID:Surface properties of dioleoyl-sn-glycerol-3-ethylphosphocholine, a cationic phosphatidylcholine transfection agent, alone and in combination with lipids or DNA. 1651 81

Mixed monolayers of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoyl-phosphatidylserine are compressed beyond their collapse pressure. Primary and secondary folds that grow perpendicular to the compression direction are observed using Brewster angle microscopy. The secondary fold velocity is measured with a fast charge-coupled device camera. We observe a reduction in secondary fold speed when increasing the mole fraction of the softer DPPC component in the monolayer. The fracture kinetics follows theoretical predictions for the fold coarsening dynamics of uniaxially stressed three-dimensional systems.
 ...
PMID:Fold-speed control in collapsing mixed phospholipid monolayers. 1685 77

The surface pressure (pi)-area (A), the surface potential (DeltaV)-A, and the dipole moment (mu( perpendicular))-A isotherms were obtained for monolayers made from a ganglioside originated from echinoderms [Diadema setosum ganglioside (DSG-1)], dipalmitoylphosphatidylcholine (DPPC), dimyristoylphosphatidylethanolamine (DMPE), cholesterol (Ch), and their combinations. Monolayers spread on several different substrates were investigated at the air/water interface by the Wilhelmy method, ionizing electrode method, fluorescence microscopy (FM) and atomic force microscopy (AFM). Surface potentials (DeltaV) of pure components were analyzed using the three-layer model proposed by Demchak and Fort [R.J. Demchak, T. Fort, J. Colloid Interface Sci. 46 (1974) 191-202]. The new finding was that DSG-1 was stable and showed a liquid-expanded film and that its monolayer behavior of DeltaV was sensitive for the change of the NaCl concentration in the subphase. Moreover, the miscibility of DSG-1 and three major lipids in the two-component monolayers was examined by plotting the variation of the molecular area and the surface potential as a function of the DSG-1 molar fraction (X(DSG-1)), using the additivity rule. From the A-X(DSG-1) and DeltaV(m)-X(DSG-1) plots, partial molecular surface area (PMA) and apparent partial molecular surface potential (APSP) were determined at the discrete surface pressure. The PMA and APSP with the mole fraction were extensively discussed for the miscible system. The miscibility was also investigated from the two-dimensional phase diagrams. Furthermore, a regular surface mixture, for which the Joos equation was used for the analysis of the collapse pressure of two-component monolayers, allowed calculation of the interaction parameter (xi) and the interaction energy (-Deltavarepsilon) between them. The observations using fluorescence microscopy and AFM image also provide us the miscibility in the monolayer state.
 ...
PMID:Mode of interaction of ganglioside Langmuir monolayer originated from echinoderms: three binary systems of ganglioside/DPPC, ganglioside/DMPE, and ganglioside/cholesterol. 1693 Sep 59

Gramicidin A, a polypeptide antibiotic forming transmembrane ion channels, has been incorporated into a Langmuir monolayer formed by a semifluorinated alkane (SFA). In this work, partially fluorinated tetracosane, perfluorohexyloctadecane (F6H18), has been applied, aiming at finding a suitable matrix for gramicidin A to be transferred onto solid support for a biosensor design. For this purpose, the physiological conditions were of special interest (mixed monolayers containing low gramicidin proportion and the surface pressure of 30 mN/m). Mixed monolayers of gramicidin and SFA were found to be miscible within the whole range of mole fractions. A very significant increase of the stability of SFA monolayer has been found in the presence of gramicidin, even at such a low proportion as X(gramicidin) = 0.1, which is reflected in a 3.5-fold increase of the collapse pressure value of mixed monolayer as compared to the film from pure SFA. This interesting phenomenon has been interpreted as being due to the existence of a strong dipole-dipole interaction between both film-forming molecules. Opposite sign of the measured electric surface potential for gramicidin and SFA, resulting from different directions of the dipole moment vectors in both film molecules, implies that the ordered, antiparallel orientation of the dipole moments in the mixed gramicidin/SFA system can be responsible for its extremely high stability.
 ...
PMID:Gramicidin A channel in a matrix from a semifluorinated surfactant monolayer. 1700 4

To determine how coexistence of liquid-expanded (LE) and tilted-condensed (TC) phases in phospholipid monolayers affects collapse from the air/water interface, we studied binary films containing dioleoyl phosphatidylcholine-dipalmitoyl phosphatidylcholine (DPPC) mixtures between 10 and 100% DPPC. Previously published results established that this range of compositions represents the LE-TC coexistence region at the equilibrium spreading pressure of 47 mN/m. When held at 49.5 mN/m on a captive bubble, the extent of total collapse fit with the LE area predicted by the phase diagram. The kinetics of collapse, however, when normalized for changes in the LE area, slowed with increasing mole fraction of DPPC. Surface area expressed as stretched exponential functions of time yielded an Avrami exponent that decreased from 1 for the homogeneously LE film to 0.3 for DPPC > or = 70%. Microscopic studies showed that the largest changes in kinetics occurred when either alterations of the initial composition or the process of collapse induced the films to cross the percolation threshold, so that the LE phase became divided into isolated domains. Our results show that although coexisting solid and fluid phases collapse to extents that are independent, the kinetics of collapse, corrected for differences in LE area, depend on the distribution of the two phases.
 ...
PMID:Distribution of coexisting solid and fluid phases alters the kinetics of collapse from phospholipid monolayers. 1707 41

We present a study of Langmuir isotherms and 2D bulk moduli of binary lipid mixtures, where changes in monolayer collapse pressure (Pic) are followed while varying the relative amounts of the two components. For monolayers containing dipalmitoylphosphocholine (DPPC) with either hexadecanol (HD) or palmitic acid (PA), a distinctly non-monotonic change in Pic is observed with varying composition. At low mole fractions, there is a slight decrease in Pic as films get richer in DPPC, while a sharp increase to pure DPPC-like values is observed when the mole fraction exceeds approximately 0.7. The sudden transition in collapse pressure is explained using the principles of rigidity percolation, and important ramifications of this phenomenon for biological surfactant are discussed.
 ...
PMID:Headgroup percolation and collapse of condensed langmuir monolayers. 1707 43


<< Previous 1 2 3 4 5 Next >>