Biomedical subjects

M J Poznansky

Publications and source records attributed to M J Poznansky.

At least 19 recordsLinked to original sources

PubMed1999

Low density lipoprotein binding induces asymmetric redistribution of the low density lipoprotein receptors in endothelial cells.

The uptake and transport of cholesterol-carrying low density lipoprotein (LDL) by the arterial wall is a continuous dynamic process, contributing to the cholesterol homeostasis in the plasma and in the cellular components of the vessel wall. Upon exposure to endothelial cells (EC), LDL interacts in part, with specific surface receptors (LDL-R). In this study we questioned: (i) the distribution of LDL receptors on the apical and basal cell membranes in endothelial cells; (ii) the role of LDL receptors in the control of cholesterol homeostasis and (iii) the translocation of LDL receptor across the EC. To this purpose bovine aortic EC were cultured on filters in a double-chamber system, in Dulbecco's medium supplemented either with 10% fetal calf serum (FCS) or with 10% lipoprotein-deficient serum (LPDS). The cells were exposed for 3h to 13H]acetate (40 microCi) added to both compartments of the cell culture inserts. The newly synthesized [3H]cholesterol was detected by thin layer chromatography and quantified by liquid scintillation counting. The LDL-R were detected in EC protein homogenates by immunoblotting using a monoclonal antibody against LDL-R (IgG-C7); the intracellular pathway of LDL-R was examined by electron microscopy using a complex made of protein A 5 nm or 20 nm colloidal gold particles and an anti-LDL receptor antibody (Au-PA-C7). To evaluate the distribution and the transport of LDL-R from one cell surface to the other, EC grown in LPDS were radioiodinated either on the apical or on the basolateral surface, incubated on the same surface with LDL, and subsequently biotinylated on the opposite non-radiolabeled surface. The EC were further solubilized and the protein extract immunoprecipitated with anti-LDL-R antibody or with mouse IgG (as control). The eluted antigen-antibody complexes were precipitated with streptavidin-agarose beads, solubilized, and subjected to SDS-PAGE. The results showed that: (a) the LDL-R were present on both endothelial cell fronts; (b) using the complex Au-PA-C7, the LDL-R were localized in endothelial plasmalemmal vesicles as well as coated pits and coated vesicles in multivesicular bodies and lysosomes, irrespective of the cell surface exposed to the complex; (c) biochemical assays indicated that upon ligand binding, the LDL-R were translocated preferentially from the apical to the basal plasma membrane.

Acetates↗

PubMed1996

The insulin-mimetic agent vanadate promotes receptor endocytosis and inhibits intracellular ligand-receptor degradation by a mechanism distinct from the lysosomotropic agents.

Vanadate (sodium orthovanadate) is an insulin-mimetic agent and phosphotyrosine phosphatase inhibitor that has been proposed as a potential therapeutic agent for diabetes. We previously reported that vanadate decreased the number of cell-surface insulin receptors but inhibited receptor degradation in cultured lymphocytes (IM-9) (1). To determine whether vanadate affected receptors without intrinsic tyrosine kinase activity, its effects on LDL and transferrin receptors and their ligands were examined. Vanadate exposure resulted in a dose- and time-dependent decrease in LDL binding to cultured human fibroblasts associated with a decrease in cell surface receptor number while total solubilized cell LDL receptors increased. Vanadate also inhibited the LDL-mediated downregulation of total cellular LDL receptors in the absence and presence of cycloheximide consistent with an inhibition of LDL receptor degradation. In the case of the ligand, vanadate augmented the accumulation of intact 125I-LDL associated with an inhibition of up to 80% of the ability of LDL to decrease cholesterol synthesis. Since these actions were similar to the effects of lysosomotropic agents, we examined the effect of vanadate on intraendosomal pH using the fluorescent probe acridine orange. In contrast with chloroquine and NH4Cl, vanadate did not neutralize the pH of the acidic intracellular compartment. Furthermore, after a transient insulin-like effect, chronic exposure to vanadate diminished 125I-diferric transferrin binding to rat adipocytes. In contrast with the inhibitory action of NH4Cl, intracellular 59Fe uptake remained unaffected and was proportional to cell-surface binding capacity in the presence of vanadate. These data demonstrate a chronic effect of vanadate to promote the accumulation of intracellular receptors and to inhibit ligand and receptor degradation. The latter effect is not mediated by pH changes, appears to be localized to a late endosomal/lysosomal compartment, and suggests a possible role for tyrosine dephosphorylation in the regulation of receptor-ligand degradation.

Adipocytes↗

PubMed1995

Dual role of melanins and melanin precursors as photoprotective and phototoxic agents: inhibition of ultraviolet radiation-induced lipid peroxidation.

Ultraviolet radiation (UVR) is one of the risk factors for skin cancer and the main inducer of melanin pigmentation, the major protective mechanism of mammalian skin against radiation damage. The melanin pigments, eumelanin and pheomelanin, are likely to be important in protection against UVR, but their precursors are generally considered as phototoxic. The available data suggest DNA damage as the mechanism of phototoxicity. However, the effect of melanin precursors on membrane damage through lipid peroxidation, another important and probably more relevant (from the point-of-view of the melanosomal confinement of these molecules) mechanism of phototoxicity, not known. As a model system for UVR-melanin-membrane interactions, we irradiated liposomes in the presence of eumelanin, pheomelanin and two of their major precursors, 5,6-dihydroxyindole (DHI) and 5-S-cysteinyldopa (SCD). The presence of the two melanin precursors substantially reduced the formation of lipid peroxidation products resulting from UVR exposure. The antioxidant activity of the melanin precursors was diminished under strong prooxidant conditions (presence of Fe3+). These results suggest that melanin precursors may have an important role in the protection of skin against the harmful effects of UVR including photocarcinogenesis.

Animals↗

PubMed1994

Oxidation of spin trap 5,5-dimethyl-1-pyrroline-1-oxide in an electron paramagnetic resonance study of the reaction of methemoglobin with hydrogen peroxide.

The possibility that methemoglobin (metHb) may function as a biological Fenton reagent to produce hydroxyl radical from hydrogen peroxide is investigated by electron paramagnetic resonance (EPR) spin-trapping techniques. The spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) gives a nine-line EPR spectrum and no hydroxyl radical or superoxide spin adduct signals for the metHb/H2O2 system. From the known hyperfine splitting constants, the spectrum is assigned to 5,5-dimethylpyrrolidone-2(2)-oxyl-(1) (DMPOX), an oxidized derivative of DMPO. The likely involvement of the peroxidase activity of metHb in this reaction is suggested by the oxidation of DMPO to DMPOX by horseradish peroxidase as well. Furthermore, peroxidase inhibitors prevent the formation of DMPOX. Spectrophotometric assays confirm the peroxidase activity of metHb toward typical phenolic and nonphenolic substrates under the conditions used for the EPR experiments. The visible absorption spectra indicate the formation of a ferrylHb intermediate and its reduction by DMPO. Glutathione and ascorbic acid compete with DMPO as electron donors in the reaction to form thiyl and ascorbate radicals. Neither hydroxyl radical nor any other signal is observed when N-tert-butyl-alpha-phenylnitrone (PBN) is used as the spin trap in the metHb/H2O2 system. It is concluded that methemoglobin-bound iron may not catalyze the Fenton reaction forming hydroxyl radical, but can oxidize a variety of substrates, including DMPO, in a peroxidase-type reaction.

Ascorbic Acid↗

PubMed1993

Inhibition of superoxide-generating NADPH oxidase of human neutrophils by lazaroids (21-aminosteroids and 2-methylaminochromans).

Lazaroids (21-aminosteroids and 2-methylaminochromans) are a new series of drugs designed and demonstrated to protect against tissue damage after trauma and/or ischemia. It has been suggested that the protective effects of lazaroids are derived from their potent actions to inhibit iron-dependent lipid peroxidation, but whether this is sufficient to explain their therapeutic effects is unknown. In an effort to better understand their mechanism of action, these drugs were tested for other modes of antioxidant activity such as scavenging superoxide and hydroxyl radicals and inhibition of production of oxygen free radicals by human neutrophils stimulated with phorbol myristate acetate. Using an ESR spin-trapping technique, with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap for superoxide and hydroxyl radicals, we found that the lazaroids U74500A and U78518F are, at best, weak scavengers of superoxide radicals whereas U78518F is a strong scavenger of hydroxyl radicals. In addition, lazaroids were found to be strong inhibitors (60-80% inhibition at 50 microM) of the superoxide-generating NADPH oxidase of human neutrophils. Inhibition of NADPH oxidase by lazaroids in cell-free systems suggested the action to be on the activated enzyme rather than on the process of activation. This may represent an important mode action of lazaroids and suggests their potential use in ischemic/inflammatory conditions involving oxygen free radical production by activated phagocytic cells.

Animals↗

PubMed1993

Superoxide dismutase (SOD)-catalase conjugates. Role of hydrogen peroxide and the Fenton reaction in SOD toxicity.

Superoxide dismutase (SOD) has been championed as an effective antioxidant for the treatment of ischemia-reperfusion injury in a wide variety of tissues. Unfortunately a bell-shaped dose-response curve has been observed, whereby SOD at higher concentrations loses its effectiveness and may even enhance the extent of reperfusion injury. Using the xanthine/xanthine oxidase reaction to generate superoxide radicals, we have attempted to examine the role of the Fenton reaction in SOD toxicity observing that high SOD levels along with micromolar concentrations of Fe2+ greatly increased the production of the highly toxic hydroxyl radical. The production of superoxide radicals and their conversion to hydroxyl radicals were measured by using the spin-trapping agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and electron spin resonance (ESR). Attempts to counter the toxicity of SOD involved the covalent conjugation of SOD to catalase in an effort to lower the available free H2O2 and thus minimize the extent of the Fenton reaction. The conjugate was tested in both the xanthine/xanthine oxidase system and a rat heart model of ischemia-reperfusion. In the xanthine/xanthine oxidase model, the combination of SOD and Fe2+ results in an enhanced production of hydroxyl radicals which is inhibited by the inclusion of catalase. In reperfused ischemic hearts, working at levels of free SOD which were either toxic or failed to give any protection against reperfusion injury, an equivalent amount of SOD conjugated to catalase resulted in an 80% return to normal mechanical function of the reperfused hearts. We attribute the toxicity of free SOD in hearts subjected to ischemia-reperfusion injury to the production of hydroxyl radicals as a result of the increased Fenton reaction. This reaction is inhibited by the presence of catalase conjugated to SOD.

Animals↗

PubMed1992

Electron spin resonance study on the permeability of superoxide radicals in lipid bilayers and biological membranes.

The permeability of lipid bilayers and biological membranes to superoxide free radicals was examined by using superoxide dismutase (SOD)-loaded lipid vesicles and SOD-loaded erythrocyte ghosts. After exposing SOD lipid vesicles and SOD ghosts to enzymatically produced superoxide radicals and using spin-trapping and electron spin resonance (ESR) techniques, we found that SOD entrapped within erythrocyte ghosts effectively scavenges external O2.- while SOD inside the lipid bilayers has no effect. These results confirm that O2.- is able to cross through a biological plasma membrane but not across a pure lipid bilayer. The data provide instruction as to how and where anti-oxidant therapy is to be approached relative to the site of oxygen free radical production.

Cell Membrane Permeability↗

PubMed1992

The effects of ischemia and ischemia-reperfusion on bacterial translocation, lipid peroxidation, and gut histology: studies on hemorrhagic shock in pigs.

The bacterial translocation hypothesis was tested in two studies (acute and subacute) in a porcine model of hemorrhagic shock. Male pigs (30-40 kg each) under general anesthesia had their femoral vein, femoral artery, and portal vein catheterized. After stabilization (1 hour) they were bled (40% of blood volume) over 30 minutes, then maintained in the hypotensive state (MAP = 30-40 mm Hg) for 2 hours, following which, according to randomization, they entered the control group or were resuscitated with whole blood (WB group) or with lactated Ringer's solution (LR group). In the acute study, the mesenteric efferent lymphatic was also cannulated, the control group was not resuscitated, and the animals remained under general anesthesia to the end of the experiment (8.5 hours), when gut tissue was obtained for histologic study and measurement of lipid peroxidation. In the subacute study, the control group was not bled, the animals were awakened at 6.5 hours, and the portal vein catheter remained in situ until 48 hours. In both studies, samples of portal blood were obtained for culture at regular intervals and on completion, samples from mesenteric lymph nodes (MLNs) for culture were taken in the acute study, and in the subacute study samples from MLNs, spleen, and liver were obtained. In the acute study significant bacterial translocation to the MLNs and portal blood did not occur among the controls (n = 3), the LR group (n = 5), and the WB group (n = 6). Significant evidence of lipid peroxidation was found in both the LR and WB groups. Histologic assessment showed no difference among the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Effect of intrathecal superoxide dismutase and catalase on oxyhemoglobin-induced vasospasm in monkeys.

A gel consisting of agarose and oxyhemoglobin (OxyHb) was developed so that, when placed in the subarachnoid space, OxyHb would be slowly released, simulating lysis of erythocytes after subarachnoid hemorrhage. The system was used to investigate the importance of reactions mediated by free radicals in the genesis of OxyHb-induced vasospasm in monkeys. Seventeen monkeys were randomly assigned to have subarachnoid placement, on Day 0, of one of the following: 1) agarose gel alone (n = 2); 2) agarose plus OxyHb (n = 3); 3) agarose plus OxyHb plus intrathecal administration of superoxide dismutase and catalase (n = 6); and 4) agarose plus OxyHb plus intrathecal administration of placebo (n = 6). Vasospasm was assessed by comparison of angiograms performed on Day 0 and 7 days after subarachnoid placement of compounds, and by electron microscopy. OxyHb alone caused significant reduction in the diameter of the middle cerebral artery (40 +/- 8%, P less than 0.005, paired t test), which was associated with ultrastructural damage to smooth muscle. Treatment with superoxide dismutase plus catalase or with placebo attenuated vasospasm of the middle cerebral artery, although significant narrowing persisted in both groups (27 +/- 12% and 26 +/- 13%, respectively, P less than 0.05, paired t test). Analysis of variance showed no difference in the degree of vasospasm between groups exposed to subarachnoid placement of OxyHb. Cerebrospinal fluid aspirated from the cisterna magna on Day 7 contained elevated activity of superoxide dismutase in animals that received treatment. Malondialdehyde was undetectable in cerebrospinal fluid after subarachnoid placement of agarose alone, although it was present in similar amounts in all groups that received subarachnoid placement of OxyHb. Since intrathecal superoxide dismutase and catalase failed to protect against OxyHb-induced vasospasm, mechanisms mediated by free radicals may not be important in its genesis. As only one combination of doses of superoxide dismutase and catalase was administered, however, it may be that other dosage schedules might be efficacious.

Animals↗

PubMed1992

Neonatal jaundice and bilirubin encephalopathy: a clinical and experimental reappraisal.

Hyperbilirubinemia and bilirubin encephalopathy are well-known occurrences in the neonatal period. The fact that bilirubin might be toxic to neural cells stems from the neurological picture that has emerged and the associated hyperbilirubinemia. Studies of the relationship between hyperbilirubinemia in healthy full-term infants and the long-term consequences showed little or no effect of bilirubin. Nevertheless, bilirubin is still considered toxic to premature infants and infants with hemolysis. In addition, in spite of a fairly detailed understanding of the chemistry of bilirubin and the biochemistry of bilirubin metabolism, the primary target of its toxic effect is still not known. The difficulties in analyzing the results are due to the variation in experimental designs, the use of different animal models and cell systems and the use of unstable bilirubin solutions. We review some of the problems related to clinical and experimental studies of bilirubin toxicity.

Animals↗

PubMed1991

Low density lipoprotein receptors on epithelial cell (Madin-Darby canine kidney) monolayers. Asymmetric distribution correlates with functional difference.

Low density lipoprotein (LDL) receptors are present on both the apical and basal surfaces of confluent monolayers of Madin-Darby canine kidney (MDCK) epithelial cells grown on gelatin-coated polycarbonate filters. Although there is only a single species of receptor protein present, as shown by immunoblotting, the receptors on the two surfaces were found to behave differently. LDL receptors on the basal surface show all of the characteristics of the LDL receptor described in fibroblasts in that their number is dependent upon the sterol (or LDL) content of the medium; however, regulation is only affected by LDL in the medium in contact with the basal side. In contrast, the apical surface LDL receptors are not regulated by the presence of LDL in the media on either the apical or basal surface. LDL particles can be transported across the monolayer in a temperature-dependent and -specific manner from the apical to the basal sides of the cell, but not in the opposite direction. The binding of 125I-LDL to both surfaces can be effectively inhibited not only by unlabeled LDL and very low density lipoprotein, but also by an antibody directed against the LDL receptor. The data suggest that the LDL receptors on the two aspects of the cell surface are biochemically identical, but differ in function. Thus, the basal surface receptor is involved in the control of cell cholesterol homeostasis, while that on the apical surface is responsible for the transport of LDL to the basal side.

Animals↗

PubMed1990

Effect of FCCP on tight junction permeability and cellular distribution of ZO-1 protein in epithelial (MDCK) cells.

The effect of the uncoupler of oxidative phosphorylation, FCCP (carbonylcyanide p-trifluoromethoxyphenylhydrazone), on the tight junction of Madin-Darby canine kidney cells was examined. FCCP induced an abrupt decrease in the transepithelial electrical resistance of the confluent monolayers over a period of 20 s. When FCCP was withdrawn from the incubation medium, the monolayer resistance recovered to close to the original level in less than 2 h. Staining of the tight junction-associated protein ZO-1 showed that the changes in transepithelial electrical resistance were accompanied by a diffusing of the protein away from cell peripheries and a reconcentration to the tight junction areas following resistance recovery. Intracellular pH was decreased by FCCP on a similar time-scale with no obvious changes in ATP levels over this time-course. These data suggest that the uncoupler FCCP has a profound effect on tight junction permeability and cellular distribution of the tight junction protein ZO-1 in the epithelial cells and that it probably acts by breaking down proton gradients and altering intracellular pH.

Animals↗

PubMed1990

Bilirubin-neural cell interaction: characterization of initial cell surface binding leading to toxicity in the neuroblastoma cell line N-115.

The toxicity of bilirubin to the nervous system might be due to its effect on several key enzyme reactions occurring in the intracellular compartment as suggested by in vitro studies. The question of how bilirubin, a molecule with poor solubility in water and organic solvents, interacts with the plasma membrane and reaches intracellular targets is unclear. In an attempt to get some insight into this problem, we have measured the uptake of bilirubin from bilirubin-albumin solutions by the murine neuroblastoma cell line N-115. At a constant total concentration of bilirubin, the initial rate, as well as the extent of uptake, increases with increasing bilirubin to albumin molar ratio (B/A). The binding is reversible, at least partially, as indicated by the ability of albumin to extract cell-bound bilirubin. The cellular uptake of bilirubin was found to depend also on the concentration of bilirubin, on temperature and on pH. The results are not consistent with either a carrier-mediated transport or passive diffusion across the plasma membrane. The data, however, seem to fit a multistep binding of bilirubin to the plasma membrane proposed for the interaction of bilirubin with synaptosomal plasma membrane vesicles, erythrocyte ghosts and lipid vesicles. These studies, thus, reveal the complexity of the binding interaction at the level of the plasma membrane and leave open the question of transport across the membrane.

Albumins↗

PubMed1990

Lipid peroxidation inactivates rat liver microsomal glycerol-3-phosphate acyl transferase. Effect of iron and copper salts and carbon tetrachloride.

Lipid peroxidation is known to affect the activity of several enzymes including microsomal enzymes such as glucose-6-phosphatase; but its effect on the enzymes of lipid biosynthesis has not been investigated. Glycerol-3-phosphate acyltransferase (GPAT) represents the first committed step and probably the rate limiting step in glycerolipid synthesis and thus may be a good candidate for study. Rat liver microsomal GPAT was assayed after preincubating the microsomes under conditions known to induce peroxidation. In 30 min, 10 microM Fe2+ can diminish the activity by as much as 80%. The inactivating effect can be blocked to different extents by several antioxidants, while ascorbic acid enhances it. These effects, along with the concomitant measurement of lipid peroxidation, indicate that microsomal GPAT activity is inactivated by lipid peroxidation in a sensitive and rapid fashion. This is further confirmed by the inactivating effect of carbon tetrachloride, which is known to induce lipid peroxidation in microsomes. Fe3+ also inactivates the enzyme, but at a higher concentration. Copper salts inactivate GPAT by a mechanism apparently different from that of iron. The mechanism might involve a direct sulfhydryl modification by copper and lipid peroxidation apparently different from that induced by iron. It is suggested that the inactivation of GPAT by lipid peroxidation could accelerate the process of membrane disintegration caused by lipid peroxidation in pathological conditions involving free radical-mediated tissue injury.

Acyltransferases↗

PubMed1990

A modified tetramethylbenzidine method for measuring lipid hydroperoxides.

A simple and sensitive spectrophotometric method for measuring lipid peroxides and peroxides in general is described. The method was developed by modifying an existing method based on the peroxidase activity of hemoglobin with tetramethylbenzidine as the electron donor. The modifications resulted in much improved sensitivity and reproducibility. With the modified method lipid peroxides as low as 2 nmol can be measured, a high sensitivity compared with other spectrophotometric methods. The absorbance is linear over a wide range of concentrations. It is suggested that this modified method in combination with the commonly used thiobarbituric acid method will give a better quantitation of lipid peroxidation.

Animals↗

PubMed1990

Cholesterol-mediated regulation of HMG-CoA reductase in microsomes from human skin fibroblasts and rat liver.

3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity was determined in microsomes from human skin fibroblasts and rat liver that had been variously manipulated in vivo or in tissue culture to up- and down-regulate the enzyme. The cholesterol content of these microsomal preparations was then altered by depletion to or enrichment from either cholesterol-free or cholesterol-rich lipid vesicles. Microsomes from human skin fibroblasts responded to cholesterol depletion by increasing HMG-CoA reductase activity and by decreasing it in response to cholesterol enrichment. This was independent of the initial enzyme activity or the tissue culture conditions. Alterations in cholesterol content of rat liver microsomes in vitro failed to demonstrate any significant changes in HMG-CoA reductase activity whether the microsomes started with low enzyme activity (cholesterol-fed rats) or with high enzyme activity (cholestyramine-treated rats). The results are discussed in relation to previously published data and in respect to differences in the control of the human skin fibroblast and rat liver enzymes.

Animals↗

PubMed1990

Characterization of the ZO-1 protein in endothelial and other cell lines.

A high molecular weight tight junction-associated protein, ZO-1, has been demonstrated in liver (hepatocytes) and in both epithelium and endothelium. We carried out studies to examine the presence of the protein in vascular endothelial cell cultures and several other types of cultured cells, and the relationship between the ZO-1 protein content and confluency of endothelial cell monolayers. Immunofluorescence labelling of endothelial monolayers and two types of epithelial monolayers, IEC-6 and MDCK, with monoclonal antibody against ZO-1 protein localized the protein to the cell peripheries. Its association with the cell periphery only occurred when cells had contact with one another as demonstrated in endothelial cells. We have been able to show a positive correlation between the ZO-1 content of the cells and the extent of monolayer confluency in the endothelial cells by immunoblotting. The protein is much less expressed in nonconfluent endothelial cell monolayers and totally absent from mouse myeloma cultures. The presence and confluence-related expression of the protein in endothelium give support to the hypothesis that tight junctions exist in confluent endothelial cells and that the ZO-1 protein is expressed under the conditions where tight junction interactions occur.

Animals↗

PubMed1989

Curvature and composition-dependent lipid asymmetry in phosphatidylcholine vesicles containing phosphatidylethanolamine and gangliosides.

The effect of curvature on transbilayer lipid asymmetry in vesicles is investigated using vesicles of different sizes (30-140 nm) prepared by sonication and polycarbonate filter extrusion techniques. The transbilayer distributions of phosphatidylethanolamine and gangliosides are measured using 2,4,6-trinitrobenzenesulphonic acid and Clostridium perfringens neuraminidase as non-penetrating probes, respectively. The distribution of phosphatidylethanolamine in a phosphatidylcholine/phosphatidylethanolamine (4:1, molar ratio) system is more or less symmetric and curvature seems to have little effect. However, the distribution of gangliosides in a phosphatidylcholine/ganglioside (10:1, molar ratio) system is asymmetric in favour of the outer layer in smaller vesicles, the asymmetry disappearing as the degree of curvature decreases. In a phosphatidylcholine/phosphatidylethanolamine/ganglioside (8:2:1, molar ratio) system, both phosphatidylethanolamine and gangliosides distribute asymmetrically, indicating a composition-dependent asymmetric distribution of phosphatidylethanolamine. In this system asymmetry also increases with increasing curvature. The asymmetric distribution of gangliosides in vesicles of low curvature may be due to their long headgroup and larger headgroup surface area in accordance with the theoretical predictions of Israelachvili et al. (Biochim. Biophys. Acta 470 (1977) 185-201).

Chromatography, Gel↗