scispace - formally typeset
Search or ask a question

Showing papers on "Membrane lipids published in 1988"


Journal ArticleDOI
TL;DR: Lipid biochemistry has remained a fairly esoteric branch of molecular cell biology, but this situation is now gradually changing with the discovery of phosphoinositide involvement in signal transduction.
Abstract: One of the challenges of contemporary cell biology is to unravel how the molecular composition of the different cellular compartments is generated and maintained during the cell cycle. In animal cells most of the efforts have been directed toward the study of how newly synthesized proteins are transported to their correct cellular destinations, whereas the lipids, which make up the framework of the membranes in the cell, have been given much less attention. Lipid biochemistry has remained a fairly esoteric branch of molecular cell biology. This situation is now gradually changing with the discovery of phosphoinositide involvement in signal transduction (Ber- ridge,

1,378 citations


Journal Article
TL;DR: It is demonstrated that CD14 is a member of the family of PI-anchored proteins and suggest that soluble forms of CD14 represent molecules that completely lack thePI-anchoring system.
Abstract: CD14 is a myeloid differentiation Ag expressed primarily on peripheral blood monocytes and macrophages. Although its function is unknown, the CD14 gene maps to a region encoding several myeloid growth factors and receptors. Analysis of the CD14 protein sequence deduced from the cDNA shows that although the CD14 protein contains a characteristic leader peptide, it lacks a characteristic transmembrane region, suggesting that CD14 may be anchored to the membrane via glycosylphosphatidylinositol (PI). Treatment of monocytes as well as a CD14-expressing neuroglioma cell line with PI-phospholipase C removed CD14 from the cell surface. Furthermore, monocytes from a patient with paroxysmal nocturnal hemoglobinuria, a disease characterized by lack of expression of other PI-linked proteins, failed to express CD14. Interestingly, the CD14-expressing neuroglioma cell line, which had been transfected with a single CD14 cDNA, released a soluble form of CD14 into the supernatant. Soluble forms of CD14 have previously been observed in serum of normal individuals and in culture supernatants of CD14+ cells. Biosynthetic experiments reveal that this soluble form of CD14 (48 kDa), which is smaller than the form released from the membrane by PI-phospholipase C (53 kDa), does not contain ethanolamine, the first constitutent of the PI-anchoring system. These studies demonstrate that CD14 is a member of the family of PI-anchored proteins and suggest that soluble forms of CD14 represent molecules that completely lack the PI-anchoring system.

649 citations


Journal ArticleDOI
TL;DR: Cecropin AD was the most effective voltage-dependent pore-forming peptide and was also the most potent antibacterial peptide against several test organisms.
Abstract: Cecropins, positively charged antibacterial peptides found in the cecropia moth, and synthetic peptide analogs form large time-variant and voltage-dependent ion channels in planar lipid membranes in the physiological range of concentration. Single-channel conductances of up to 2.5 nS (in 0.1 M NaCl) were observed, which suggests a channel diameter of 4 nm. Channels formed by the peptides cecropin AD and MP3 had a permeability ratio of Cl-/Na+ = 2:1 in 0.1 M NaCl. A comparative study of the three cecropins, cecropins A, B, and D, and of six synthetic analogs allowed determination of structural requirements for pore formation. Shorter amphipathic peptides did not form channels, although they adsorbed to the bilayer. A flexible segment between the N-terminal amphipathic region and the C-terminal more hydrophobic region of the peptide was required for the observation of a time-variant, voltage-dependent conductance. Cecropin AD was the most effective voltage-dependent pore-forming peptide and was also the most potent antibacterial peptide against several test organisms. A positive surface charge or cholesterol in the bilayer reduced the conductances caused by cecropin AD or MP3 by at least 5-fold. This behavior is consistent with the known insensitivity of eukaryotic cells to cecropins. Our observations suggest that the broad antibacterial activity of cecropins is due to formation of large pores in bacterial cell membranes.

502 citations


Journal ArticleDOI
TL;DR: Intact magnetosomes of Aquaspirillum magnetotacticum were purified from broken cells by a magnetic separation technique and revealed the magnetite to be enclosed by a lipid bilayer admixed with proteins.
Abstract: Intact magnetosomes of Aquaspirillum magnetotacticum were purified from broken cells by a magnetic separation technique. Electron microscopic and chemical analyses revealed the magnetite to be enclosed by a lipid bilayer admixed with proteins. Lipids were recovered in fractions expected to contain (i) neutral lipids and free fatty acids, (ii) glycolipids and sulfolipids, and (iii) phospholipids (in a weight ratio of 1:4:6). Phospholipids included phosphatidylserine and phosphatidylethanolamine. Two of the numerous proteins detected in the magnetosome membrane were not found in other cell membranes or soluble fractions.

415 citations


Journal ArticleDOI
TL;DR: PE/DOTAP vesicles show substantial lipid mixing with negatively charged vesicle containing high proportions of phosphatidylcholine, as well as with human erythrocyte ghosts, on a time scale of a few minutes.
Abstract: Lipid vesicles with a positive surface charge have been prepared by using mixtures of phosphatidylethanolamine (PE) and phosphatidylcholine (PC) together with low mole fractions of a cationic lipid analogue, 1,2-bis(oleoyloxy)-3-(trimethylammonio)propane (DOTAP). We have used measurements of vesicle aggregation, lipid mixing, contents mixing, and contents leakage to examine the interactions between these vesicles and similar vesicles that carry a negative surface charge. Mixtures of vesicles with opposite surface charges aggregate readily at physiological or lower ionic strengths, and the extent of this aggregation is enhanced for vesicles that contain high proportions of PE relative to PC. Mixing of lipids and aqueous contents can also be observed between such vesicles, particularly when the vesicles contain substantial proportions of PE. Surprisingly, these latter processes are strongly promoted by monovalent salts and do not proceed at very low ionic strengths. PE/DOTAP vesicles show substantial lipid mixing with negatively charged vesicles containing high proportions of phosphatidylcholine, as well as with human erythrocyte ghosts, on a time scale of a few minutes. These interactions are strongly promoted both by the presence of high levels of PE in the cationic vesicles and by the presence of complementary surface charges on the two membrane populations.

339 citations


Journal ArticleDOI
TL;DR: A model for the sorting process is presented, the central point of which is that the two sets of lipids laterally segregate into microdomains that bud to form vesicles delivering the lipids to the apical and the basolateral plasma membrane domains, respectively.
Abstract: Apical and basolateral membrane domains of epithelial cell plasma membranes possess unique lipid compositions. The tight junction, the structure separating the two domains, forms a diffusion barrier for membrane components and thereby prevents intermixing of the two sets of lipids. The barrier apparently resides in the outer, exoplasmic leaflet of the plasma membrane bilayer. First data are now available on the generation of these differences in Madin-Darby canine kidney (MDCK) cells, grown on filter supports. Experiments in which fluorescent precursors of apical lipids were introduced into the cell have demonstrated that upon biosynthesis apical lipids are sorted from basolateral lipids in an intracellular compartment. In this paper we present a model for the sorting process, the central point of which is that the two sets of lipids laterally segregate into microdomains that bud to form vesicles delivering the lipids to the apical and the basolateral plasma membrane domains, respectively.

248 citations


Journal ArticleDOI
14 Jul 1988-Nature
TL;DR: It is demonstrated here, using mutants of Escherichia coli defective in the synthesis of the major anionic membrane phospholipids, that phosphatidylglycerol is involved in the translocation of newly synthesized outer-membrane proteins across the inner membrane.
Abstract: Newly synthesized proteins to be exported out of the cytoplasm of bacterial cells have to pass across the inner membrane. In Gram-negative bacteria ATP, a membrane potential, the products of the sec genes and leader peptidases (enzymes which cleave the N-terminal signal peptides of the precursor proteins) are required. The mechanism of translocation, however, remains elusive. Important additional roles for membrane lipids have been repeatedly suggested both on theoretical grounds and on the basis of experiments with model systems but no direct evidence had been obtained. We demonstrate here, using mutants of Escherichia coli defective in the synthesis of the major anionic membrane phospholipids, that phosphatidylglycerol is involved in the translocation of newly synthesized outer-membrane proteins across the inner membrane. AD - Department of Biochemistry, University of Utrecht, The Netherlands.

246 citations


Journal ArticleDOI
TL;DR: By screening directly for alterations in lipid acyl-group composition, several mutants of Arabidopsis that lack the plastid pathway are identified, providing an insight into the nature of the regulatory mechanisms that allocate lipids for membrane biogenesis.
Abstract: The leaf membrane lipids of many plant species, including Arabidopsis thaliana (L.) Heynh., are synthesized by two complementary pathways that are associated with the chloroplast and the endoplasmic reticulum. By screening directly for alterations in lipid acyl-group composition, we have identified several mutants of Arabidopsis that lack the plastid pathway because of a deficiency in activity of the first enzyme in the plastid pathway of glycerolipid synthesis, acyl-ACP:sn-glycerol-3-phosphate acyltransferase (EC 2.3.1.15) (where ACP is acyl carrier protein). The lesion results in an increased synthesis of lipids by the cytoplasmic pathway that largely compensates for the loss of the plastid pathway and provides nearly normal amounts of all the lipids required for chloroplast biogenesis. However, the fatty acid composition of the leaf membrane lipids of the mutants is altered because the acyltransferases associated with the two pathways normally exhibit different substrate specificities. The remarkable flexibility of the system provides an insight into the nature of the regulatory mechanisms that allocate lipids for membrane biogenesis.

225 citations


Journal ArticleDOI
TL;DR: Manipulating the lipid composition or fluidizing the HIV membrane, or both, may provide an untried therapeutic approach for viral stability and infectivity.
Abstract: Lipid analyses of the human immunodeficiency virus (HIV) propagated in Hut 78 cells indicated a low total lipid/protein ratio, a high cholesterol/phospholipid molar ratio, and major phospholipids consisting of phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, and phosphatidylserine; comparable lipid profiles were noted for human erythrocytes and other RNA viruses. Electron spin resonance (ESR) studies of HIV labeled with 5-nitroxide stearate (N-oxy-4',4'-dimethyloxazolidine derivative of ketostearate) showed a low "fluidity" at 37 degrees C, similar to other enveloped RNA viruses and erythrocytes and probably due to the high cholesterol/phospholipid ratio. Ethanol (50%) completely disrupts the envelope, contributing to the rapid inactivation of HIV by ethanol. Contrarily, heating to 57 degrees C causes much less fluidization, and this heating may play a role in the slower viral inactivation at high temperatures. Should a critical minimum ordering in the HIV envelope be necessary for viral stability and infectivity, manipulating the lipid composition or fluidizing the HIV membrane, or both, may provide an untried therapeutic approach.

208 citations


Journal ArticleDOI
TL;DR: The results suggest the importance of both the head-group and acyl chain composition of the rod outer segment lipids in the visual process and the molecular features of recombinant membranes that are necessary for the photochemical function of rhodopsin.
Abstract: We have investigated the molecular features of recombinant membranes that are necessary for the photochemical function of rhodopsin. The magnitude of the metarhodopsin I to metarhodopsin II phototransient following a 25% +/- 3% bleaching flash was used as a criterion of photochemical activity at 28 degrees C and pH 7.0. Nativelike activity of rhodopsin can be reconstituted with an extract of total lipids from rod outer segment membranes, demonstrating that the protein is minimally perturbed by the reconstitution protocol. Rhodopsin photochemical activity is enhanced by phosphatidylethanolamine head groups and docosahexaenoyl (22:6 omega 3) acyl chains. An equimolar mixture of phosphatidylethanolamine and phosphatidylcholine containing 50 mol% docosahexaenoyl chains results in optimal photochemical function. These results suggest the importance of both the head-group and acyl chain composition of the rod outer segment lipids in the visual process. The extracted rod lipids and those lipid mixtures favoring the conformational change from metarhodopsin I to II can undergo lamellar (L alpha) to inverted hexagonal (HII) phase transitions near physiological temperature. Interaction of rhodopsin with membrane lipids close to a L alpha to HII (or cubic) phase boundary may thus lead to properties which influence the energetics of conformational states of the protein linked to visual function.

164 citations


Journal ArticleDOI
TL;DR: Binding equilibria of common bile salts and different mixtures of membrane lipids were correlated with BS-induced structural changes of large unilamellar vesicles, with transition of vesicle to mixed micelles (MM), and with successive transformations of MM.
Abstract: Binding equilibria of common bile salts (BS) and different mixtures of membrane lipids were correlated with BS-induced structural changes of large unilamellar vesicles, with transition of vesicles to mixed micelles (MM), and with successive transformations of MM. At very low BS concentrations, in the outer vesicle monolayer definite BS/lipid aggregates are formed, the size and BS binding strength of which depend on the BS and lipid species involved. At increasing BS concentrations, binding to the membranes is hampered, and above a critical BS content, membrane stress due to asymmetric BS binding leads to formation of transient membrane holes, as shown by inulin release from the vesicles. Independent of the BS and lipid species, membrane solubilization starts at a ratio r = 0.3 of bound BS/lipid. Increasing phosphatidylserine, phosphatidylethanolamine, and cholesterol contents stabilize the lecithin membrane against BS to different degrees and in different ways, whereas the destabilization by sphingomyelin is probably due to the enhancement of the membrane gel-liquid transition temperature. Conjugation of the BS with glycine or taurine has a modulating effect on membrane hole formation, rather than on lipid solubilization. Diphenylhexatriene fluorescence anisotropy indicates a BS-induced drop of the internal membrane order and its restoration during membrane solubilization. At higher concentrations ursodeoxycholate induces additional condensation, whereas the other BS cause internal disorder in the MM. Above ratios r of approximately 8:1, we found a release of BS from these MM and suggest a rodlike structure for them. The results were discussed with respect to BS/membrane interactions during lipid excretion from the liver cell.

Journal ArticleDOI
TL;DR: The existence of similarly linked glycoproteins in the yeast Saccharomyces cerevisiae is established and it is found that sec18 cells, when grown at 37 degrees C, do add phospholipid anchors to newly synthesized glycoprotein, which indicates that these anchors are added in the rough endoplasmic reticulum.
Abstract: A number of plasma membrane glycoproteins of mammalian and protozoan origin are released from cells by phosphatidylinositol-specific phospholipase C. Some of these proteins have been shown to be attached to the lipid bilayer via a covalently linked, structurally complex glycophospholipid. Here we establish the existence of similarly linked glycoproteins in the yeast Saccharomyces cerevisiae. The most abundant of these is a tightly membrane-bound glycoprotein of 125 kd. The detergent-binding moiety of this protein can be removed by phosphatidylinositol-specific phospholipase C of bacterial origin or from Trypanosoma brucei. Metabolic labeling indicates that the protein contains covalently attached fatty acid and inositol. It also contains the cross-reacting determinant (CRD), an antigen found previously on the glycophospholipid anchor of protozoan and mammalian origin. Treatment of the protein with endoglycosidases F and H results in a 95-kd species. In the secretion mutant sec18, grown at 37 degrees C, the vesicular transport of glycoproteins is reversibly blocked between the rough endoplasmic reticulum and the Golgi apparatus. We find that sec18 cells, when grown at 37 degrees C, do add phospholipid anchors to newly synthesized glycoproteins. This indicates that these anchors are added in the rough endoplasmic reticulum.

Journal ArticleDOI
TL;DR: In this paper, neutral lipid domains are intercalated with the bilayer lipid of the plasma membrane and a functional role for these neutral lipids is also proposed based on plasma membrane alterations which occur with cellular stimulation, with the acquisition of resistance to anti-cancer drugs, and in metastatic cells.

Book ChapterDOI
TL;DR: This chapter describes procedures in cyanobacterial lipid analysis, including extraction and fractionation of lipids, analysis of their fatty acids, determination of positional distribution of fatty acids within thelipids, and analysis of lipid molecular species.
Abstract: Publisher Summary This chapter describes procedures in cyanobacterial lipid analysis, including extraction and fractionation of lipids, analysis of their fatty acids, determination of positional distribution of fatty acids within the lipids, and analysis of lipid molecular species Cyanobacterial cells contain two types of membrane, the plasma membrane and thylakoid membranes, which are distinct from each other in their composition of proteins, lipids, and pigments The composition of the fatty acids of the lipids in both types of membrane changes with growth temperature so that cyanobacterial cells adapt themselves to the environmental temperature Major lipid classes in cyanobacterial membranes are monogalactosyl diacylglycerol (MGDG), monoglucosyl diacylglycerol (GIcDG), digalactosyl diacylglycerol (DGDG), sulfoquinovosyl diacylglycerol (SQDG), and phosphatidylglycerol (PG) Thin-layer chromatography (TLC) is a convenient method for separating major classes of lipids The content and composition of fatty acids in lipids are determined by gas chromatographic analysis of the methyl esters which are obtained by methanolysis of the lipids Methanolysis is generally performed without isolating lipids from the silica gel

Journal ArticleDOI
TL;DR: For biochemical studies of lipid synthesis in Chlorella, the modified Bligh and Dyer provides the most quantitative and reproducible recovery of all Chloreella lipid classes while minimizing artifacts due to the extraction procedure.

Journal ArticleDOI
TL;DR: The rate of transbilayer movement of cholesterol was measured in intact human erythrocytes, consistent with an asymmetric distribution of cholesterol in ERYthrocyte membranes, with the majority ofolesterol in the inner leaflet.

Journal ArticleDOI
TL;DR: Administration of high-dose ethinylestradiol to rats decreases bile flow, Na,K-ATPase specific activity, and liver plasma membrane fluidity, while Liver plasma membrane fractions showed no change in free cholesterol or cholesterol/phospholipid molar ratio.
Abstract: Administration of high-dose ethinylestradiol to rats decreases bile flow, Na,K-ATPase specific activity, and liver plasma membrane fluidity. By use of highly purified sinusoidal and bile canalicular membrane fractions, the effect of ethinylestradiol administration on the protein and lipid composition and fluidity of plasma membrane fractions was examined. In sinusoidal fractions, ethinylestradiol (EE) administration decreased Na,K-ATPase activity (32%) and increased activities of alkaline phosphatase (254%), Mg2+-ATPase (155%), and a 160-kDa polypeptide (10-fold). Steady-state and dynamic fluorescence polarization was used to study membrane lipid structure. Steady-state polarization of diphenylhexatriene (DPH) was significantly higher in canalicular compared to sinusoidal membrane fractions. Ethinylestradiol (5 mg/kg per day for 5 days) selectively increased sinusoidal polarization values. Similar changes were demonstrated with the probes 2- and 12-anthroyloxystearate. Time-resolved fluorescence polarization measurements indicated that EE administration for 5 days did not change DPH lifetime but increased the order component (r infinity) and decreased the rotation rate (R). However, 1 and 3 days after EE administration and with low doses (10-100 micrograms/kg per day for 5 days) the Na,K-ATPase, bile flow, and order component were altered, but the rotation rate was unchanged. Vesicles prepared from total sinusoidal membrane lipids of EE-treated rats, as well as phospholipid vesicles, demonstrated increased DPH polarization, as did intact plasma membrane fractions. Liver plasma membrane fractions showed no change in free cholesterol or cholesterol/phospholipid molar ratio, while esterified cholesterol content was increased with high-dose but not low-dose ethinylestradiol.(ABSTRACT TRUNCATED AT 250 WORDS)

Journal ArticleDOI
TL;DR: How changes in membrane lipids, especially fatty acid composition, may modulate physiological properties of membranes, such as fluidity, and cel...
Abstract: Biological membranes consist of lipid bilayers composed primarily of phospholipids and cholesterol. Proteins with important membrane functions, such as enzymes, receptors and transporters are enclosed in the lipid bilayer. A basic question is whether interactions with lipids in the bilayer can modulate the activity of membrane proteins. From the standpoint of cellular physiology and metabolic regulation, a critical point has been whether changes in membrane lipid composition actually occur in living cells as a response to changes in the lipid availability, and if so, whether the changes are of sufficient magnitude to influence membrane functions. During the last decade an extensive amount of information regarding these issues has been obtained, especially from studies with liposomes and mammalian cells in culture. The purpose of this review is briefly to describe how changes in membrane lipids, especially fatty acid composition, may modulate physiological properties of membranes, such as fluidity, and cel...

Journal ArticleDOI
TL;DR: Since oxidation of unsaturated fatty acids to hydroperoxides is the first event in lipid peroxidation, activation of PKC by hydroperoxy fatty acids may be an early cellular response to oxidative stress.

Journal ArticleDOI
TL;DR: In order to obtain more insight in the initial steps of the process of protein translocation across membranes, biophysical investigations were undertaken on the lipid specificity and structural consequences of penetration of the PhoE signal peptide into lipid model membranes and on the conformation of the signal peptides adopted upon interaction with the lipids.
Abstract: In order to obtain more insight in the initial steps of the process of protein translocation across membranes, biophysical investigations were undertaken on the lipid specificity and structural consequences of penetration of the PhoE signal peptide into lipid model membranes and on the conformation of the signal peptide adopted upon interaction with the lipids When the monolayer technique and differential scanning calorimetry are used, a stronger penetration is observed for negatively charged lipids, significantly influenced by the physical state of the lipid but not by temperature or acyl chain unsaturation as such Although the interaction is principally electrostatic, as indicated also by the strong penetration of N-terminal fragments into negatively charged lipid monolayers, the effect of ionic strength suggests an additional hydrophobic component Most interestingly with regard to the mechanism of protein translocation, the molecular area of the peptide in the monolayer also shows lipid specificity: the area in the presence of PC is consistent with a looped helical orientation, whereas in the presence of cardiolipin a time-dependent conformational change is observed, most likely leading from a looped to a stretched orientation with the N-terminus directed toward the water This is in line also with the determined peptide-lipid stoichiometry Preliminarymore » /sup 31/P NMR and electron microscopy data on the interaction with lipid bilayer systems indicate loss of bilayer structure« less

Journal Article
Quinn Pj1
TL;DR: The importance of lipid phase behaviour is discussed in the context of membrane stability at different temperatures in this review of plasma membrane and cytoplasmic membranes of plants.
Abstract: The plasma membrane and cytoplasmic membranes of plants, like those of animal cells, are composed of lipids and proteins that are often glycosylated. Likewise, the composition from one membrane type to another is highly heterogeneous. There is some evidence to suggest that the composition, particularly of the lipid component, may change in response to environmental conditions such as temperature, water stress, etc. as well as during growth, development and ultimately senescence of the cell. It is believed that these changes are required to adjust the physical characteristics of membrane structures so that they may perform their necessary physiological tasks when environmental factors change. If the environmental conditions are altered beyond the normal limits within which the plant survives, the cell membranes are often found to undergo gross structural changes. These structural perturbations include phase separation of the membrane constituents and are associated with characteristic disturbances of function such as loss of selective permeability and transport processes. In most instances, the observed phase separations appear to be driven by phase changes in the membrane lipids. Some lipids extracted from algae and plant membranes are known to exist in a bilayer gel phase when dispersed in aqueous systems at the growth temperature while other lipid fractions are in a liquid-crystalline state. Nearly all membranes contain varying proportions of their lipid complement that do not form bilayer structures under such conditions and most commonly adopt an hexagonal-II arrangement. In this review the importance of lipid phase behaviour is discussed in the context of membrane stability at different temperatures.

Journal ArticleDOI
01 May 1988-Lipids
TL;DR: As quantified spectrophotometrically, true MDA production during myocardial membrane peroxidation was identical in kinetics and in amount to the production of TBA-reactive substance from the peroxidized isolated membrane lipids, demonstrating that significant non-MDA species are generated during the per oxidation of cardiac membranes.
Abstract: When exposed to xanthine oxidase (superoxide)-dependent, iron-promoted Fenton chemistry, purified cardiac membranes evidenced, by the thiobarbituric acid (TBA) test, a virtually instantaneous peroxidative response with a maximal linear rate of 5.8 nmol malondialdehyde (MDA)-equivalents/mEquivalents lipid ester reacted/min. Yet when the lipids purified from these same membranes and reconstituted into liposomes were peroxidized under identical reaction conditions, the TBA test indicated that a pronounced (∼20-min) lag period preceded a maximal peroxidation rate of only 2.1 nmol MDA-equivalents/ mEquivalents lipid ester reacted/min. After 120 min of peroxidation, the cardiac membranes yielded some 300 nmol TBA-reactive MDA-equivalents/mEquivalent ester, whereas the isolated membrane lipids evidenced ∼40% less TBA-reactivity. To verify that these quantitative and kinetic differences in membrane (phospho)-lipid peroxidation occurred with removal of the lipids from their membrane milieu, the MDA produced during both cardiac membrane peroxidation and the peroxidation of the lipids derived therefrom was isolated as its free anion by ion-pair high-pressure liquid chromatography. As quantified spectrophotometrically, true MDA production during myocardial membrane peroxidation was identical in kinetics and in amount to the production of TBA-reactive substance from the peroxidized isolated membrane lipids. These results demonstrate that significant non-MDA. TBA-reactive species are generated during the peroxidation of cardiac membranes, especially before the maximal rates of bona fide MDA production. As a direct consequence, artifactual levels and kinetics of membrane lipid peroxidation do result.

Journal ArticleDOI
TL;DR: Results indicate renal ischemia causes rapid duration-dependent reversible loss of surface membrane polarity in proximal tubule cells.
Abstract: Total renal ischemia for various time intervals (0–50) min) resulted in the rapid and duration-dependent redistribution of polarized membrane lipids and proteins in renal proximal tubule cells. Following only 15 min of ischemia, apical membrane enrichment of NaK-ATPase, normally a basolateral membrane (BLM) enzyme, had increased (1.6±0.6vs. 2.9±1.2,P<0.01). In vivo histochemical localization of NaK-ATPase showed reaction product throughout the apical microvillar region. PTH-stimulatable adenylate cyclase, another BLM protein, was also found in ischemic but not control apical membrane fractions. One dimensional SDS-PAGE showed four bands, present in control BLM and ischemic apical membranes, which could not be found in control apical membrane fractions. Immunohistochemical localization of leucine aminopeptidase (LAP) showed the enzyme was limited to the apical domain in control cells. Following ischemic injury (50 min), LAP staining could be seen within the cell and along the BLM. Following 24 hr of reperfusion, the BLM distribution of LAP was further enhanced. With cellular recovery from ischemic injury (5 days), LAP was again only visualized in the apical membrane. Duration-dependent alterations in apical and BLM lipids were also observed. Apical sphingomyelin and phosphatidylserine and the cholesterol-tophospholipid ratio decreased rapidly while apical phosphatidylcholine and phosphatidylinositol increased. Taken together, these results indicate renal ischemia causes rapid duration-dependent reversible loss of surface membrane polarity in proximal tubule cells.

Journal ArticleDOI
TL;DR: Using a fluorescent probe, significantly increased levels of peroxides are found in human endothelial cells infected by Rickettsia rickettsii, suggesting that the increased peroxide levels in infected cells may be lipid peroxide, degradation products of free radical attack on polyenoic fatty acids.
Abstract: Cells infected by Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever, display unusual intracellular morphological changes characterized by dilatation of the membranes of the endoplasmic reticulum and outer nuclear envelope. These changes are consistent with those that might be expected to occur following peroxidation of membrane lipids initiated by oxygen radical species, such as the hydroxyl radical or a variety of organic radicals. Using a fluorescent probe, we have found significantly increased levels of peroxides in human endothelial cells infected by R. rickettsii. Studies with desferrioxamine, an iron chelator effective in preventing formation of the hydroxyl radical from hydrogen peroxide and the superoxide free radical, reduced peroxide levels in infected cells to those found in uninfected cells. This observation suggests that the increased peroxides in infected cells may be lipid peroxides, degradation products of free radical attack on polyenoic fatty acids. The potential for lipid peroxidation as an important mechanism in endothelial cell injury caused by R. rickettsii is discussed.

Journal ArticleDOI
TL;DR: The low permeability of the membrane lipid bilayer to most hydrophilic species prevents the rapid dissipation of transbilayer solute gradients co­ established by membrane transport systems and intracellular metabolism and thus assists in the maintenance of a cytosolic environment favorable to cellular homeostasis.
Abstract: Membrane transport proteins (carriers) catalyze transmembrane movements of hydrophilic molecular species. To perform this function, carriers employ a variety of mechanisms for transmembrane solute flux that are distinct from and more rapid than leakage or non-Stokesian transbilayer diffusion of solutes (37). The low permeability of the membrane lipid bilayer to most hydrophilic species prevents the rapid dissipation of transbilayer solute gradients co­ established by membrane transport systems and intracellular metabolism and thus assists in the maintenance of a cytosolic environment favorable to cellular homeostasis. In addition to providing a permeability barrier, the membrane lipid bilayer provides a matrix for the attachment of membrane proteins. Most integral membrane proteins contain extensive, hydrophilic (extramembranous) and hydrophobic (membrane spanning) sequences. As a consequence, transverse protein reorientations (flip-flop) within the lipid bilayer arc highly improbable

Journal ArticleDOI
TL;DR: The integral domain of human erythrocyte band 3 was reconstituted into a series of well-defined lipids and found to be significantly stabilized by increasing the degree of saturation of the fatty acyl chains and by elevating the cholesterol content of the membrane.

Journal ArticleDOI
TL;DR: There appears to be a correlation between the number of water molecules a lipid binds to the phase preference of that lipid, and the lipids, like phosphatidylcholine, which favours the lamellar phase bind far greater number ofWater molecules as compared to those, likeosphatidylethanolamine, which favour the hexagonal phase.

Journal ArticleDOI
TL;DR: In this article, a nonspecific lipid transfer protein was used to vary the cholesterol/phospholipid molar ratio of rat proximal small intestinal microvillus membranes in order to assess the possible role of cholesterol in modulating enzymatic activities of this plasma membrane.

Journal ArticleDOI
TL;DR: Human myelin basic protein, a long‐lived brain protein, undergoes gradual racemization of its amino acids, primarily aspartic acid and serine, which is compatible with a model in which each MBP molecule interacts with adjacent cytoplasmic layers of myelin membrane through a β‐sheet on one surface and loops and helices on the other surface, thereby stabilizing the myelin multilamellar structure.
Abstract: Human myelin basic protein (MBP), a long-lived brain protein, undergoes gradual racemization of its amino acids, primarily aspartic acid and serine. Purified protein was treated at neutral pH with trypsin to yield peptides that were separated by HPLC using a C18 column. Twenty-nine peptides were isolated and analyzed for amino acid composition and aspartate racemization. Each aspartate and asparagine in the protein was racemized to a different extent, ranging from 2.2 to 17.1% D isomer. When the racemization was examined in terms of the beta-structure model of MBP, a correlation was observed in which six aspartate/asparagine residues assumed to be associated with myelin membrane lipids showed little racemization (2.2-4.9% D isomer), whereas five other aspartate residues were more highly racemized (9.9-17.1% D isomer). Although the observed aspartate racemization may be related to steric hindrance by neighboring residues and/or the protein secondary structure, interaction of aspartates with membrane lipids may also be a major factor. The data are compatible with a model in which each MBP molecule interacts with adjacent cytoplasmic layers of myelin membrane through a beta-sheet on one surface and loops and helices on the other surface, thereby stabilizing the myelin multilamellar structure.

Journal ArticleDOI
TL;DR: It was found that mild acid hydrolysis in 0.18% methanolic HCl produced only one core lipid product from GL-1 or two core lipids from the total polar lipid fraction, which differed from the authentic C 20,20 diether in that it contained a hydroxyl group on C-3 of the phytanyl chain at the sn -3 position of glycerol.