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Showing papers on "Membrane published in 1978"


Journal ArticleDOI
12 May 1978-Science
TL;DR: The force required to separate two cells is shown to be greater than the expected electrical forces between cells, and of the same order of magnitude as the forces required to pull gangliosides and perhaps some integral membrane proteins out of the cell membrane.
Abstract: A theoretical framework is proposed for the analysis of adhesion between cells or of cells to surfaces when the adhesion is mediated by reversible bonds between specific molecules such as antigen and antibody, lectin and carbohydrate, or enzyme and substrate. From a knowledge of the reaction rates for reactants in solution and of their diffusion constants both in solution and on membranes, it is possible to estimate reaction rates for membrane-bound reactants. Two models are developed for predicting the rate of bond formation between cells and are compared with experiments. The force required to separate two cells is shown to be greater than the expected electrical forces between cells, and of the same order of magnitude as the forces required to pull gangliosides and perhaps some integral membrane proteins out of the cell membrane.

4,058 citations


Journal ArticleDOI
TL;DR: In this article, the steric repulsion energy per unit area of membrane is derived as a function of temperature, membrane curvature elasticity and mean membrane spacing; it is inversely proportional to the square of the latter.
Abstract: Abstract The out-of-plane fluctuations of fluid membranes are sterically hindered in multilayer systems. The repulsive interaction associated with the steric or excluded-volume effect is studied theoretically by two methods. The interaction energy per unit area of membrane is derived as a function of temperature, membrane curvature elasticity and mean membrane spacing; it is inversely proportional to the square of the latter. Steric repulsion is estimated for lecithin bilayers in water. There and in other cases, it may compete with van der Waals attraction.

847 citations


Journal ArticleDOI
TL;DR: The results indicate that cholera toxin affects the adenylate cyclase system by catalyzing an ADP-ribosylation of the 42,000-M(r) component bearing the guanyl nucleotide regulatory site.
Abstract: Treatment of pigeon erythrocyte membranes with cholera toxin and NAD+ enhanced the GTP stimulation and suppressed the F- activation of the adenylate cylase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1]. In the presence of NAD+ labeled with 32P in the AMP moiety the toxin catalyzed the covalent incorporation of radioactivity into membrane proteins with molecular weights (Mrs) of 200,000, 86,000, and 42,000. Extraction of toxin-treated membranes with Lubrol PX followed by affinity chromatography on a GTP-Sepharose column resulted in a 200-fold purification of the 42,000-Mr labeled protein and in its complete separation from the other labeled proteins. The fraction containing the purified GTP-binding component from toxin-treated membranes conferred an enhanced GTP-stimulated activity on adenylate cyclase solubilized from nontreated membranes. Likewise, the addition of GTP-binding fraction from nontreated membranes to an enzyme solubilized from toxin-treated membranes restored F- stimulation of the adenylate cyclase. The toxin-induced modification of adenylate cyclase and the incorporation of radioactivity into the 42,000-Mr protein were partially reversed upon incubation with toxin and nicotinamide at pH 6.1. The results indicate that cholera toxin affects the adenylate cyclase system by catalyzing an ADP-ribosylation of the 42,000-Mr component bearing the guanyl nucleotide regulatory site.

815 citations


Journal ArticleDOI
TL;DR: Membrane permeability to various solutes was determined in part by a new technique which utilized phase-contract microscopy; when impermeable vesciles exclude added solutes such as sucrose, refractive index differences are created between vesicle contents and surrounding medium, so that the vesicles appear bright in the phase microscope.
Abstract: In studies of the minimum physiochemical requirements for lipid membrane formation, we have made liposomes from dilute, aqueous dispersions of C(8)-C(18) single-chain amphiphiles. In general, membrane formation from ionic soaps and detergents requires the presence of uncharged amphiphiles. Vesicles were characterized by phase-contrast microscopy, by trapping of ionic dyes, as well as by negativestain and freez-frature electron microscopy. They were typically heterogeneous in size, but the average diameter could be experimentally varied in some cases over the range of 1 to 100 micrometer. Uni-, oligo-, and multilamellar vesicles were observed. Membrane permeability to various solutes was determined in part by a new technique which utilized phase-contract microscopy; when impermeable vesciles exclude added solutes such as sucrose, refractive index differences are created between vesicle contents and surrounding medium, so that the vesicles appear bright in the phase microscope. Permeant solutes do not produce this effect. Spectrophotometric permeability determinations confirmed the results of this technique and provided quantitative measures of permeability. Monoalkyl liposomes have potential uses as models of biomembranes and in drug delivery. They are also relevant to the prebiotic origin of biomembranes.

512 citations


Journal ArticleDOI
TL;DR: One of the major proteins of the outer membrane of Escherichia coli, the matrix protein (porin), has been isolated by detergent solubilisation and the findings are consistent with the assumption that the protein forms large aqueous channels in the membrane.

503 citations


Journal ArticleDOI
TL;DR: Likely mechanisms for proton transport through biomembranes are explored, and a simple proton pump can be described that can be reversed into a molecular motor driven by an electrochemical potential across the membrane.
Abstract: Likely mechanisms for proton transport through biomembranes are explored. The fundamental structural element is assumed to be continuous chains of hydrogen bonds formed from the protein side groups, and a molecular example is presented. From studies in ice, such chains are predicted to have low impedance and can function as proton wires. In addition, conformational changes in the protein may be linked to the proton conduction. If this possibility is allowed, a simple proton pump can be described that can be reversed into a molecular motor driven by an electrochemical potential across the membrane.

502 citations


Journal ArticleDOI
23 Nov 1978-Nature
TL;DR: It is reported that membranes may be prepared from A-431 cells that retain the ability to bind 125I-labelled EGF in a specific manner, and the binding of EGF to these membranes in vitro results in a marked stimulation of the phosphorylation of endogenous proteins in the presence of [γ-32P]ATP.
Abstract: EPIDERMAL GROWTH FACTOR (EGF) forms a complex with plasma membrane receptors in intact cells that initiates a series of biochemical events resulting in increased cell growth in vivo and in vitro1. The interaction of EGF with membrane receptors has been demonstrated in crude membrane preparations2, but no biochemical alteration of the membrane resulting from hormone binding has been detected. To clarify the molecular mechanisms regulating cell proliferation, specific biochemical reactions initiated by mitogens such as EGF need to be investigated in cell-free systems. As the human epidermoid carcinoma cell line A-431 has an extraordinarily high concentration of EGF receptors3,4 (2–3 x 106 receptors per cell), we have used a crude membrane preparation from these cells to look for an EGF-dependent alteration of membrane structure and/or function. We report here that (1) membranes may be prepared from A-431 cells that retain the ability to bind 125I-labelled EGF in a specific manner, and (2) the binding of EGF to these membranes in vitro results in a marked stimulation of the phosphorylation of endogenous proteins in the presence of [γ-32P]ATP.

420 citations



Journal ArticleDOI
12 Jan 1978-Nature
TL;DR: The mean position of the deuterated segments within the membrane can be determined in most cases to a precision of better than ±1 Å, and the average orientation of the phosphocholine group in the gel state as well as the liquid crystalline state is almost parallel to the membrane surface.
Abstract: NEUTRON diffraction combined with the use of selectively deuterated lipids can provide detailed information on the molecular structure of membranes. Because of the large difference between the coherent scattering length of hydrogen ( −3.74 fermis) and deuterium (6.67 fermis) the deuterated membrane segments show up as intense peaks in the neutron density profile and can thus easily be located in the membrane1–3. We have applied this method to bilayer membranes of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), selectively deuterated at 12 different positions in the polar head group and the hydrocarbon chains. We report here that the mean position of the deuterated segments within the membrane can be determined in most cases to a precision of better than ±1 A. The average orientation of the phosphocholine group in the gel state as well as in the liquid crystalline state is almost parallel to the membrane surface. In the gel state the two hydrocarbon chains are out of step by about 1.8 A, and water penetrates up to the glycerol backbone of the lipid molecules.

356 citations



Journal ArticleDOI
TL;DR: The results provide direct evidence for Na+-coupled electrogenic active L-glutamate transport by rat brain membrane vesicles and the dependence on internal potassium ions is discussed.
Abstract: Membrane vesicles, isolated after osmotic shock of synaptosomal rat brain fractions, actively accumulate L-glutamate. This process requires the presence of external sodium ions and internal potassium ions and is driven by artifically imposed ion gradients as the sole energy source. Either an Na+ gradient (out is greater than in) or a K+ gradient (in is greater than out) or both can be utilized to concentrate L-glutamate inside the vesicles. Transport is enhanced by valinomycin or by external thiocyanate ions and is about 50% inhibited by the proton ionophore carbonyl cyanide m-chlorophenylhydrazone. This transport thus appears to be stimulated by a membrane potential (interior negative). The glutamate transporter, the Km of which has been determined to be 3 micrometer, is specific for L-glutamate. The transport process is unaffected by ouabain but is strongly inhibited by p-hydroxymercuribenzoate as well as by nigericin, which collapses the energizing ion gradients across this membrane. Unlike the sodium dependent, but potassium independent active accumulation of gamma-aminobutyric acid in these vesicles (Kanner, B.I. (1978) Biochemistry 17, 1207) active L-glutamate uptake is not dependent on the presence of small monovalent anions in the external medium. The results provide direct evidence for Na+-coupled electrogenic active L-glutamate transport by rat brain membrane vesicles. The dependence on internal potassium ions is discussed.

Journal ArticleDOI
TL;DR: A method for separating the outer and inner membranes of Pseudomonas aeruginosa PAO1 in the absence of added ethylenediaminetetraacetic acid was devised, yielding two outer membrane fractions which show the same protein pattern on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but differ substantially in their relative contents of phospholipids.
Abstract: A method for separating the outer and inner membranes of Pseudomonas aeruginosa PAO1 in the absence of added ethylenediaminetetraacetic acid was devised. The method yields two outer membrane fractions which show the same protein pattern on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but differ substantially in their relative contents of phospholipids. One of these outer membrane fractions and the inner membrane fraction are less than 4% cross-contaminated, as judged by the content of typical inner and outer membrane markers. The outer membrane contains four major protein bands with apparent molecular weights of 37,000, 35,000, 21,000 and 17,000. Vesicles reconstituted from lipopolysaccharide and phospholipids were impermeable to all saccharides included in the vesicles during vesicle formation. When the vesicles contained outer membrane proteins, they fully retained only those saccharides of greater than 9,000 molecular weight, suggesting that the exclusion limit of the outer membrane of P. aeruginosa for saccharides is substantially larger than the figure (500 to 600 daltons) obtained for certain enteric bacteria. The advantages and potential disadvantages of having an outer membrane with a higher exclusion limit for hydrophilic substances are discussed.

Journal ArticleDOI
21 Sep 1978-Nature
TL;DR: It is reported here that the enzymatic methylation of phosphatidylethanolamine in erythrocyte membranes induces a marked increase of the bulk membrane fluidity.
Abstract: PHOSPHOLIPIDS are a major component of biomembranes and provide the fluid matrix for protein movement and organisation. Membrane fluidity has been closely related to the biological and biochemical processes such as transport of chemicals, cell fusion, and protein rotation and diffusion1,2. Genetic, nutritional and temperature manipulation have been used to alter the fluidity of the cell membrane3,4, but physiological and biochemical events that regulate membrane fluidity are still unknown. We report here that the enzymatic methylation of phosphatidylethanolamine in erythrocyte membranes induces a marked increase of the bulk membrane fluidity.

Journal ArticleDOI
16 Feb 1978-Nature
TL;DR: A model for membrane fusion induced by oleic acid is proposed, which it is suggested may also apply to fusion events in vivo.
Abstract: MEMBRANE fusion clearly requires that participating lipids assume some transitory non-bilayer configuration during the intermediate stages. Previous workers have suggested that intermediate micellar1 or inverted micellar2,3 structures may occur, but the precise nature of possible intermediates and their relation to the physical properties of membrane lipids are obscure. In this regard, Lucy and co-workers4–8 have shown that ‘fusogenic’ agents such as fatty acids and their derivatives induce erythrocytes to fuse. Such agents might possibly promote fusion by enabling endogenous lipids to assume non-bilayer configurations. We have therefore investigated the influence of two such fusogens on the structure of the erythrocyte (ghost) membrane using 31P NMR techniques, which have been found to be sensitive to phospholipids in non-bilayer phases9,10. We show that the incorporation of oleic acid and glycerol mono-oleate into the ghost membrane, at concentrations similar to those needed to induce cell fusion between erythrocytes in vitro, produce a well-defined transition of a variable portion of the membrane phospholipids from the bilayer phase to an hexagonal (HII) phase. These results lead us to propose a model for membrane fusion induced by oleic acid, which we suggest may also apply to fusion events in vivo.

Journal ArticleDOI
TL;DR: There is strong evidence that band 3 mediates 1:1 anion exchange across the membrane through a conformational cycle while remaining fixed and asymmetrical.
Abstract: Band 3 is the predominant polypeptide and the purported mediator of anion transport in the human erythrocyte membrane. Against a background of minor and apparently unrelated polypeptides of similar electrophoretic mobility, and despite apparent heterogeneity in its glycosylation, the bulk of band 3 exhibits uniform and characteristic behavior. This integral glycoprotein appears to exist as a noncovalent dimer of two approximately 93,000-dalton chains which span the membrane asymmetrically. The protein is hydrophobic in its composition and in its behavior in aqueous solution and is best solubilized and purified in detergent. It can be cleaved while membrane-bound into large, topographically defined segments. An integral, outer-surface, 38,000-dalton fragment bears most of the band 3 carbohydrate. A 17,000-dalton, hydrophobic glycopeptide fragment spans the membrane. A approximately 40,000-dalton hydrophilic segment represents the cytoplasmic domain. In vitro, glyceraldehyde 3-P dehydrogenase and aldolase bind reversibly, in a metabolie-sensitive fashion, to this cytoplasmic segment. The cytoplasmic domain also bears the amino terminus of this polypeptide, in contrast to other integral membrane proteins. Recent electron microscopic analysis suggests that the poles of the band 3 molecule can be seen by freeze-etching at the two original membrane surfaces, while freeze-fracture reveals the transmembrane disposition of band 3 dimer particles. There is strong evidence that band 3 mediates 1:1 anion exchange across the membrane through a conformational cycle while remaining fixed and asymmetrical. Its cytoplasmic pole can be variously perturbed and even excised without a significant alteration of transport function. However, digestion of the outer-surface region leads to inhibition of transport, so that both this segment and the membrane-spanning piece (which is selectively labeled by covalent inhibitors of transport) may be presumed to be involved in transport. Genetic polymorphism has been observed in the structure and immunogenicity of the band 3 polypeptide but this feature has not been related to variation in anion transport or other band 3 activities.

Journal ArticleDOI
TL;DR: Matrix protein from Escherichia coli was integrated into planar lipid bilayers and incorporated protein generates aqueous channels across these membranes, an observation that explains both negative resistance and inactivation at high potentials.
Abstract: Matrix protein from Escherichia coli was integrated into planar lipid bilayers. The incorporated protein generates aqueous channels across these membranes. Channels are induced irreversibly by voltage, and their number is proportional to the protein content of the membrane and stays constant over hours. They are uniform in size, with a diameter of about 1 nm and a single-channel conductance of 0.14 nS in 0.1 M NaCl. In addition to ionic conductance, the channels allow free diffusion of small, uncharged molecules. Channels assume either an open or a closed state. Membrane potentials shift this two-state equilibrium distribution in favor of closed channels, an observation that explains both negative resistance and inactivation at high potentials. Channels are not randomly distributed in the membrane but interact cooperatively within aggregates. The smallest entity inducible consists of three channels.

Journal ArticleDOI
TL;DR: Although active Na-K transport is not influenced by cholesterol enrichment of human red cells, several carrier-mediated transport pathways are inhibited and the cotransport of Na + K and similar results have been obtained by others in studies of organic acid transport and the transport of small neutral molecules such as erythritol and glycerol.
Abstract: Cholesterol and phospholipid are the two major lipids of the red cell membrane. Cholesterol is insoluble in water but is solubilized by phospholipids both in membranes and in plasma lipoproteins. Morever, cholesterol exchanges between membranes and lipoproteins. An equilibrium partition is established based on the amount of cholesterol relative to phospholipid (C/PL) in these two compartments. Increases in the C/PL of red cell membranes have been studied under three conditions: First, spontaneous increases in vivo have been observed in the spur red cells of patients with severe liver disease; second, similar red cell changes in vivo have been induced by the administration of cholesterol-enriched diets to rodents and dogs; third, increases in membrane cholesterol have been induced in vitro by enriching the C/PL of the lipoprotein environment with cholesterol-phospholipid dispersions (liposomes) having a C/PL of greater than 1.0. In each case, there is a close relationship between the C/PL of the plasma environment and the C/PL of the red cell membrane. In vivo, the C/PL mole ratio of red cell membranes ranges from a normal value of 0.09--1.0 to values which approach but do not reach 2.0. In vitro, this ratio approaches 3.0. Cholesterol enrichment of red cell membranes directly influences membrane lipid fluidity, as assessed by the rotational diffusion of hydrophobic fluorescent probes such as diphenyl hexatriene (DPH). A close correlation exists between increases in red cell membrane C/PL and decreases in membrane fluidity over the range of membrane C/PL from 1.0 to 2.0; however, little further change in fluidity occurs when membrane C/PL is increased to 2.0--3.0. Cholesterol enrichment of red cell membranes is associated with the transformation of cell contour to one which is redundant and folded, and this is associated with a decrease in red cell filterability in vitro. Circulation in vivo in the presence of the spleen further modifies cell shape to a spiny, irregular (spur) form, and the survival of cholesterol-rich red cells is decreased in the presence of the spleen. Although active Na-K transport is not influenced by cholesterol enrichment of human red cells, several carrier-mediated transport pathways are inhibited. We have demonstrated this effect for the cotransport of Na + K and similar results have been obtained by others in studies of organic acid transport and the transport of small neutral molecules such as erythritol and glycerol. Thus, red cell membrane C/PL is sensitive to the C/PL of the plasma environment. Increasing membrane C/PL causes a decrease in membrane fluidity, and these changes are associated with a reduction in membrane permeability, a distortion of cell contour and filterability and a shortening of the survival of red cells in vivo.

Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate that internal polarization may have a profound adverse effect on the water permeation rate of an asymmetric semipermeable membrane under pressure-retarded osmosis.

Journal ArticleDOI
09 Nov 1978-Nature
TL;DR: It is suggested that the physiological effects of colicin K and functionally related colicins result from their ability to form ion-permeable channels in the bacterial plasma membrane.
Abstract: The bactericidal action of colicins K, E1, Ia, and other functionally related colicins involves disruption of active transport and leakage of ions from the cell. We show that a single colicin K molecule can form a voltage-dependent, relatively nonselective, ion-permeable channel of a few picosiemens conductance in a planar phospholipid bilayer membrane. In a membrane containing many of these channels, the ratio of the number of conducting to nonconducting channels changes e-fold per 3.7 mV. We suggest that the physiological effects of colicin K and functionally related colicins result from their ability to form ion-permeable channels in the bacterial plasma membrane.

Journal ArticleDOI
TL;DR: It is postulated that melittin causes a wedge effect in membranes, which under physiological conditions, in water,melittin is in extended conformation, which is enhanced in aqueous ethanol, however in 'membrane-like' conditions it is essentially alpha-helical.

Journal ArticleDOI
TL;DR: The ratio of cholesterol to phospholipid was found to be significantly increased in both types of membrane after chronic ethanol treatment, and increased cholesterol may explain the previously observed alteration of physical properties of the membranes.

Journal ArticleDOI
TL;DR: It is shown that the brush-border membrane vesicles isolated from rat kidney cortex and from rat small intestine for transport studies are predominantly orientated right-side out.
Abstract: Orientation of rat renal and intestinal brush-border membrane vesicles was studied with two independent methods: electron-microscopic freeze-fracture technique and immunological methods. With the freeze-fracture technique a distinct asymmetric distribution of particles on the two membrane fracture faces was demonstrated; this was used as a criterion for orientation of the isolated membrane vesicles. For the immunological approach the accessibility or inaccessibility of aminopeptidase M localized on the outer surface of the cell membrane to antibodies was used. With both methods we showed that the brush-border membrane vesicles isolated from rat kidney cortex and from rat small intestine for transport studies are predominantly orientated right-side out.

Journal ArticleDOI
TL;DR: If the fractional increase in capacitance found here is a good approximation to that of biological membranes, nonlinear capacitative charge displacement derived from electrostriction is expected to be less than 1% of the total gating charge displacement found in squid axons.

Book ChapterDOI
TL;DR: This chapter explores that as an experimental model, the red cell has clear advantages in that Ca 2+ can be assessed and controlled better than in any other cell, and in that even minute selective changes in K permeability can be unambiguously determined by relatively simple methods.
Abstract: Publisher Summary This chapter concentrates on the Ca-sensitive K permeability mechanism of red cells. Although the functional role of this process is completely unknown in these cells, the red cell membrane represents an extremely convenient experimental model for the study of such a mechanism. Ca-induced K flux is so easy to measure and so richly responsive to all sorts of treatments that it has stimulated more extensive than analytical research. The chapter explores that as an experimental model, the red cell has clear advantages in that Ca 2+ can be assessed and controlled better than in any other cell, and in that even minute selective changes in K permeability can be unambiguously determined by relatively simple methods. Furthermore, investigation of the molecular nature of the Ca-sensitive K channel is still at a very early stage. Moreover, a few attempts have been made to search for specific high affinity inhibitors with which the channels can be “labeled,” their surface density can be measured, but the results so far are not very promising.

Journal ArticleDOI
TL;DR: Electrophoretic mobility and 31P NMR measurements were combined to test whether the combination of the Henry, Boltzmann and Grahame equations is capable of describing the adsorption of divalent cations of phosphatidylcholine membranes.


Journal ArticleDOI
TL;DR: Isolated outer and cytoplasmic membranes of Pseudomonas aeruginosa differed markedly in the content of 2-keto-3-deoxyoctonate and phospholipid as well as in the localization of certain enzymes.
Abstract: A method is described for the preparation of outer and cytoplasmic membranes of Pseudomonas aeruginosa, and the outer membrane proteins characterized. Isolated outer and cytoplasmic membranes differed markedly in the content of 2-keto-3-deoxyoctonate (lipopolysaccharide) and phospholipid as well as in the localization of certain enzymes (NADH oxidase, succinate dehydrogenase, D-lactate dehydrogenase, malate dehydrogenase, and phospholipase), and also in the microscopic morphology. The outer membrane preparation showed activity neutralizing a certain bacteriocin or bacteriophages, whereas the cytoplasmic membrane preparation showed no neutralizing activity. The protein composition of membrane preparations from five different strains of P. aeruginosa [P14, M92 (PAO1), PAC1, P15, and M2008 (PAT)] were determined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. More than 50 protein bands were detected in the cytoplasmic membrane preparation. The protein compositions of outer membranes from the five different strains were very similar: at least 6 major bands were found (apparent molecular weights: Band D, 50,000; band E, 45,000; band F, 33,000; bands G and H, 21,000; and band I, 8,000). The protein composition of outer membranes was affected by some physiological growth conditions. Some features of major outer membrane proteins were also studied. Band F showed anomalous migration on SDS polyacrylamide gel electrophoresis depending on the solubilizing conditions or pretreatment with TCA. Band I seemed to be a protein analogous to the lipoprotein which had been found in the outer membrane of Escherichia coli.

Journal ArticleDOI
TL;DR: The availability of a membrane binding assay that faithfully reflects the properties of the physiologic LDL receptor of intact cells should permit the characterization of this receptor in organs from intact humans and animals.

Journal ArticleDOI
TL;DR: Administration of Triton WR-1339, a nonionic detergent that corrects hepatic and serum lipid changes caused by ethinyl estradiol treatment, restored toward normal elevated membrane lipids and viscosity as well as Na(+),K(+)-ATPase activity and bile flow.
Abstract: Administration of the synthetic estrogen ethinyl estradiol (17α-ethinyl-1,3,5-estratriene-3,17β-diol) decreases hepatic Na+,K+-ATPase (ATP phosphohydrolase; EC 3.6.1.3) activity and bile flow to 50% and alters the composition and structure of surface membrane lipid in rats. Although the content of phospholipids was not changed by treatment, free cholesterol (130%) and cholesterol esters (400%) were increased in liver surface membrane fractions. These observations correlate with changes in membrane viscosity, as shown by electron spin resonance probes. Both rotational correlation time, using the isotropic probe methyl (12-nitroxyl)stearate, and the order parameter, determined by the anisotropic probe 5-nitroxylstearic acid, were significantly increased in liver surface membrane fractions from rats treated with ethinyl estradiol. Administration of Triton WR-1339, a nonionic detergent that corrects hepatic and serum lipid changes caused by ethinyl estradiol treatment, restored toward normal elevated membrane lipids and viscosity as well as Na+,K+-ATPase activity and bile flow. Although restoration of normal liver surface membrane structure and function may be due to reversal of abnormal lipid composition, detergents also may directly alter membrane enzyme activity. Addition of Triton WR-1339 in vitro increased Na+,K+-ATPase activity and reduced membrane viscosity of surface membranes from rats treated with ethinyl estradiol. Triton had no effect on either parameter in normal membrane preparations. Studies of membrane structure and function both in vivo and in vitro suggest that alterations in lipid composition may alter Na+,K+-ATPase function and bile flow.

Journal ArticleDOI
TL;DR: These protein-membrane binding characteristics agree very well with the relatedness of these proteins based on their partial amino-terminal sequences.
Abstract: The membrane-binding characteristics of six vitamin K dependent plasma proteins, which have homologous amino acid sequences, were compared. All of these proteins display calcium-dependent membrane binding and the identified equilibria for protein-membrane binding are qualitatively the same for all proteins. Quantitative characteristics of these protein-membrane interactions allow organization into distinct subgroups. Protein C and factor VII form a subgroup which has extemely low affinity for bilayer membranes; prothrombin, factor X, and protein S form the tightest complexes with membranes and factor IX displays intermediate affinity. In the presence of manganese (which substitutes for calcium in a cation-dependent protein transition), calcium titration of protein-membrane binding shows the same calcium dependence for all proteins except prothrombin which requires lower calcium. These protein-membrane binding characteristics agree very well with the relatedness of these proteins based on their partial amino-terminal sequences.