Showing papers on "Membrane lipids published in 1971"

The movement of molecules across lipid membranes: A molecular theory

Abstract: The movement of molecules across membranes is discussed in terms of thermal fluctuations in the hydrocarbon chains of the membrane lipids. The thermal motion of the hydrocarbon chains results in the formation of conformational isomers, so-called kink-isomers of the hydrocarbon chains. “Kinks” may be pictured as mobile structural defects which represent small, mobile free volumes in the hydrocarbon phase of the membrane. The diffusion coefficient of kinks is calculated to be 10−5 cm2/sec; thus kinks diffusion is a fast process. Small molecules can enter into the free volumes of kinks and migrate across the membrane together with the kinks; thus kinks may be regarded as intrinsic carriers of lipid membranes. An expression is derived from this model for the flow of molecules through lipid membranes. The calculated value for the water permeability is compatible with measurements on lipid bilayers.

STUDIES OF MEMBRANE FORMATION IN TETRAHYMENA PYRIFORMIS : II. Isolation and Lipid Analysis of Cell Fractions

Abstract: A method has been devised to fractionate cells of Tetrahymena pyriformis, yielding pure or highly enriched preparations of cilia, cilia-associated soluble material, pellicles, mitochondria, microsomes, and postmicrosomal supernatant. The method prevents the destructive action of lipolytic enzymes commonly associated with this organism. Analysis of the membrane lipids of these fractions reveals significant differences in lipid composition. Most noteworthy are the high concentrations of phosphonolipid and tetrahymanol in the surface membranes.

A spin label study of sarcoplasmic vesicles

Abstract: Spin labeled fatty acids have been incorporated as structural probes into sarcoplasmic vesicles isolated from rabbit skeletal muscle. The evaluation of the electron paramagnetic resonance spectra has yielded the following results: 1 The spin labels I (m,n) display a fast, anisotropic rotation in the sarcoplasmic membrane. The first 7 carbon-carbon bonds adjacent to the carboxyl group of the spin labeled fatty acid experience a highly ordered environment, whereas for n > 7 a pronounced increase in the flexibility of the hydrocarbon chain is observed although the system is still more ordered than pure lipid dispersions. The fluidity of the membrane is due to its lipid constituents, since a removal of the lipids leads to spectra characteristic for immobilized spin labels. 2 The comparison of several model systems leads to the assumption that a direct lipidprotein interaction must play an essential role in the organization of the membranous lipids. The effect of this interaction is to increase the stiffness of the hydrocarbon chains of the lipid moieties. 3 The activity of the calcium dependent ATPase is directly related to the fluidity of the membrane. If the enzymatic activity of a lipid deficient membrane is restored by the addition of oleic acid, the oleic acid assumes a physical state which is very similar to that of the natural membranous lipids.

The binding of botulinum toxin to membrane lipids: sphingolipids, steroids and fatty acids.

Abstract: A number of lipids known to be constituents of nerve-ending membranes were tested for their ability to inactivate botulinum toxin Inactivation of the toxin by a lipid was taken as presumptive evidence that the lipid might be the in vivo receptor for the toxin Several sphingolipids (sphingosine, galactosylceramide, glucosylceramide, lactosylceramide, cytolipin K and cytolipin R), steroids (cholesterol and deoxycholic acid) and fatty acids (palmitic acid, stearic acid, prostaglandin E1) did not affect the potency of botulinum toxin, and thus were discounted as potential toxin receptors However, the gangliosides did inactivate botulinum toxin rapidly (in less than 5 min), within a temperature range of 2°-40°C, and at ionic strengths of 005-040 Inactivation diminished as pH fell below 6 The activity of gangliosides in suppressing the potency of botulinum toxin was a function of the number of sialic acid residues in the lipid Thus, the data suggest that a molecule containing sialic acid may be the receptor for the toxin

Shared lipid phosphate carrier in the biosynthesis of teichoic acid and peptidoglycan.

Abstract: THE pathways for the formation of several bacterial wall polymers have been thoroughly investigated. In some cases it has been shown that the biosynthesis involves the participation of lipid intermediates that are concerned with the transfer and transport through the membrane, of sugar residues and related components from intracellular nucleotide precursors to polymer chains in the wall. All these membrane lipids so far isolated and identified have been shown to be the C55 polyisoprenol, undecaprenol, although it has not yet been demonstrated that they are the same isomer. Thus poly-isoprenols have been demonstrated to participate in the synthesis of O-antigen1, peptidoglycan2, 3 and mannan4.

Chemistry of phospholipids in relation to biological membranes.

Abstract: The quantitative determination of molecular species of natural phospholipids gave new information about the pairing of the fatty acid chains in a given lipid class. Cells appear to be equipped with enzymes which control the composition and pairing of hydrocarbon chains of phospholipids and display regulatory mechanism(s) which allow for adaptation of physical properties of membrane lipids to alteration in environmental conditions. Phospholipids containing various types of fatty acid combinations encountered in membranes have been prepared by chemical synthesis. Examination of these compounds in artificial membrane systems demonstrated that chain-length, degree of unsaturation, and the type of pairing of hydrocarbon chains determine the rate of diffusion of non-electrolytes and efficiency of carrier mediated transport across the hydrocarbon barrier. Comparison with natural membranes of different lipid composition revealed a close similarity with the model systems. This endorses the conclusion that the detailed chemical make-up of the lipid dictates the permeability behaviour of the region of the biological interface. The diversity of polar headgroups of phospholipids is demonstrated by the polyglycerol phospholipids of bacterial membranes, Detailed information about the structure of amino acyl and glucosamine derivatives of phosphatidyl glycerol has been obtained by combination of chemical synthesis and enzymatic methods.

Enzyme reactions in biological membranes

Abstract: Publisher Summary This chapter discusses enzyme reactions in biological membranes. A large number of cellular enzymes are located in membranes. Indeed, it is likely that most particulate enzymes are in truth membrane-bound enzymes whose particulate nature reflects their association with the lipid matrix of biological membranes. Included in this category are enzymes located in plasma membranes, mitochondria, microsomes, and in other sub-cellular organelles. In fact, if one is willing to extend the definition to proteins that catalyze the physical translocation of substrates, the class of membrane enzymes can be extended to include proteins responsible for transmembrane transport, such as bacterial permeases. Membrane lipids can also participate in enzyme-catalyzed reactions by forming covalently linked intermediates in the reaction sequence. So far, this has been shown to occur in the synthesis of macromolecules in bacteria and in all cases examined, the carrier lipids are polyiso-prenoid compounds. In general, the solubilization of membrane proteins requires the disruption of the organized membrane structure. Nonpolar bonds (lipid–lipid, lipid–protein, and protein–protein) are believed to play a major role in stabilizing the structure of membranes and it is, therefore, not surprising that agents that disrupt such bonds are often effective in solubilizing membrane-bound enzymes.

Permeability of bimolecular membranes made from lipid extracts of human red cell ghosts to sugars.

Abstract: Spherical lipid bimolecular membranes of a large surface area separating two aqueous solutions were formed from the total lipid extracts of human red cell ghosts and from their individual lipid components. The isotopic permeabilities of these membranes to biologically important sugars and to a related polyol were measured. The observedD-glucose permeabilities of the bimolecular membranes of the total lipid, phosphatidyl choline, phosphatidyl ethanolamine, sphingomyelin, and cholesterol were 2.35, 2.51, 2.23, 1.35, and 0.62×10(-10) cm/sec, respectively. These permeabilities are about four to five orders of magnitude lower than that of the intact red cell membrane. The permeabilities of the bimolecular membrane made from an identical extract of the total lipid to different sugars varied: the values forD-glucose,D-mannose,D-ribose,D-fructose, 2-deoxy-D-glucose, 3-0-methyl-D-glucose, andD-mannitol were 2.3, 2.6, 8.9, 0.38, 16.1, 11.2, and 0.44×10(-10) cm/sec, respectively. The pattern of the difference is neither parallel with nor as extensive as that observed with the intact red cell membrane. The observed permeabilities of the lipid membranes, however, agree qualitatively with what is predicted by an analysis of non-specific movements of nonelectrolytes across the cell membranes. The failure of the membrane lipids to reproduce the carrier function in a structure most closely approximating that of living membranes strongly suggests that some membrane components other than lipids are required for this function.

The effect of phospholipase C on the activity of adenosine triphosphatase and acetylcholinesterase in synaptic membranes isolated from the cerebral cortex of squirrel monkey.

Abstract: A synaptic-membrane fraction rich in junctional components and Na-K ATPase and AChE activity was isolated from the cerebral cortex of the squirrel monkey. Incubation of membrane preparations with phospholipase C decreased the activity of Na-K ATPase by 50 per cent but had no effect on the activity of AChE. Analysis of the membrane fraction showed that phospholipase C cleaved both choline phosphoglyceride and the diacyl type of ethanolamine phosphoglyceride from membrane lipids. Addition of egg lecithin at low concentrations partially restored the activity of Na-K ATPase. Kinetic studies revealed that treatment with phospholipase C may produce a non-competitive type of inhibition as a result of the cleavage of a charged phosphorylated nitrogen base from membrane lipids.

Structure of membranes and role of lipids therein.

Abstract: Publisher Summary This chapter discusses the structure of membranes and role of lipids therein The properties of membranes emerge from a specific structural arrangement of all components and as such are barely predictable from individual component properties Lipids have a very important structural function: both polar and nonpolar moieties participate in intra- and intersubunit cohesion Lipids are components of the barrier opposing the diffusion of ions and molecules across the membrane The hydrocarbon phase of the lipid barrier has a low dielectric constant This confers to myelin its electrical insulating properties A major function of this dielectric layer is, however, to give the membrane the properties of a condenser Hence, charge–charge interaction energy and electrostrictive forces become available for dynamic processes Lipids are also important to the normal function of some membrane enzymes Lipids participate in at least three additional functions The first is the establishment of a proton-conductive, water-cation monolayer The second function, closely related to the first, is the drawing of cations to the water-cation monolayer—the influence of fixed positive charges on cation movements Phospholipids provide the necessary ligands for divalent cation bridges between membrane subunits This role is important not only to membrane cohesion but also to all forms of transport with the possible exception of simple diffusion

Parallel temperature-induced changes in membrane fatty acids and in the transport of amino acids by the intestine of goldfish (Carassius auratus L.).

Abstract: 1. 1. An analysis of the fatty acid composition of goldfish intestinal mucosal membranes showed the proportion of stearic acid to rise and that of docosahexaenoic acid to fall when fish adapted to 16°C were placed in water at 30°C. These changes were complete after 48 hr. The rates at which phenylalanine and methionine crossed the intestine and the final serosal concentrations reached for these amino acids were not changed significantly by this procedure. 2. 2. Adaptation to a high temperature reduced both the serosal transfer and the ability of the intestine to concentrate valine at its serosal surface. This selective fall in amino acid transport, represented here as a change in the phenylalanine to valine serosal concentration ratio, first became apparent 48 hr after raising the environmental temperature. 3. 3. Since other adaptive processes have different time courses and those for changes in membrane lipids and amino acid transport are similar, it is suggested that the two might be related, changes in lipids altering selectively the rates at which actively transported amino acids diffuse from the mucosa into the serosal fluids.

The binding of botulinum toxin to membrane lipids: phospholipids and proteolipid.

Abstract: A number of phospholipids known to be constituents of nerve endings were tested for their ability to inactivate botulinum toxin. Substances tested included phosphatidylcholine, phosphatidalcholine, phosphatidylethanolamine, phosphatidalethanolamine, β-acyl lysolecithin, sphingomyelin, phosphatidylserine, phosphatidic acid, phosphatidylinositol and cardiolipin. Proteolipid from bovine white matter was also tested. Neutral phospholipids potentiated the toxicity in vivo of botulinum toxin, but they had no effect on the toxicity in vitro. Some, but not all, acidic phospholipids caused loss of toxicity of botulinum toxin in solutions at low pH both in vivo and in vitro. However, none of these substances when incubated with toxin under physiological conditions of temperature, pH and ionic strength, caused loss of toxin potency. The data suggest that none of these phospholipids is likely to be a toxin receptor.

Lipid Layer in Cell Membranes

Abstract: MEASUREMENTS of the extent of shrinkage of membranes which results from hydrolysis of phospholipid components by phospholipase C provide a direct indication of the area occupied by lipid in cell membranes. Maximum treatment of erythrocyte ghosts with phospholipase C (Clostridium welchii) liberates approximately 70% of the membrane phospholipid phosphorus and the surface area of the ghosts is decreased by 45–55% as calculated from diameter measurements made on spherical ghosts observed by phase contrast microscopy1 and more recently from ghost volume measurements by an exclusion technique involving the use of 14C labelled sucrose. There is strong evidence that the phospholipid molecule as a whole is displaced from the membrane but the fate of the other membrane lipids is not established although it has been demonstrated that a residual lipoprotein structure persists. To indicate the quantitative significance of the observations, however, we have assumed that all lipids are removed in the same proportions as for the phospholipid. The observed shrinkage of the membrane by 50% would then be attributed to the loss of 70% of the membrane lipid. This would indicate that lipid occupies an area corresponding to 100 × 50/70 = 70% of the overall membrane area. Should any lipid be displaced to a lesser extent, then the figure for the area occupied by lipid would be increased to more than 70%.

The labilizing effect of minute glass particles on black lipid membranes and the stabilizing action of a lipophilic glucofuranose derivative

Abstract: It was shown that sub-microscopical glass particles suspended in an electrolyte solution are capable of acting on developing synthetic lipid membranes or pre-formed bilayer lipid membranes by coming into contact with the surface of such membranes and finally entering them. Thereby pores capable of conductance develop and, as a consequence, membrane resistance decreases. The importance of the observed effects of glass particles on synthetic lipid membranes with regard to the action of such particles on biological membranes is discussed.

Structure of Cellular Membranes and Regulation of Their Lipid Composition

Abstract: Two lipid class substitution groups have been defined. Members of a group can replace each other in membranes. Similar substitution groups are found for animal cells, fungi, and bacteria, although a lipid class that occurs in many organisms may be completely absent from others. Myelin is a membrane that has the maximum amount of lipid (fully packed) and essentially all of the protein appears to bind polar lipid. Other membranes contain less lipid and more protein, some of which does not appear to bind lipid. In membranes, lipid is postulated to lie upon the protein to which it is attached by apolar bonding of carbon chains as well as ionic and hydrogen bonds through polar groups. Lipid molecules lie close to each other and interact through their carbon chains (apolar bonding). In myelin, cholesterol probably binds to acidic lipids. The maximum cholesterol level is seen in myelin and the human red blood cell in which one-half the molar amount of cholesterol equals the amount of acidic lipid (acidic phospholipids, phosphatidyl ethanolamine, sulfatide, and ganglioside). It is thus postulated that two molecules of cholesterol can bind to one of acidic lipid. The cross section of the membrane is postulated to consist of four layers of lipid and two of protein in the sequence lipid-protein-lipid-lipid-protein-lipid. In myelin which is maximally packed with lipid, the four layers are completely filled. In other membranes with less lipid and lipid-binding protein, the lipid layers are incompletely filled. In the human red blood cell, lipid appears to cover only about one-third of the protein surface. Membrane permeability to many ionic substances appears to be related to the total amount of lipid, those membranes having the most lipid being the least permeable. It is suggested that the blood-brain barrier exists because plasma membranes of cells of the nervous system contain more lipid than those of other organs and are thus more slowly penetrated by some ionic substances. The different lipid compositions of subcellular particulates of the same cell type and from different organs is correlated with the relative proportions of the different types of membranes. It is postulated that, during differentiation, levels of each type of subcellular particulate are set and that thereafter lipid composition changes follow a similar course in all organs. Some changes in membrane lipids in abnormal states are discussed.

Magnetic Resonance Studies of Membranes and Lipids

Abstract: To relate the structure of a membrane to its functional properties at the molecular level requires techniques to define the detailed organization of the membrane components, and to identify the components of the structure involved in a specific function in the intact membrane. Both problems are complicated by the multiplicity of the membrane components. The use of X-ray diffraction techniques to define the spatial relationships of the membrane components has been complicated by the dynamic motion of the membrane lipids and the absence of a high degree of order in the membrane proteins, so that the diffraction patterns contain only limited structural information. The techniques of nuclear magnetic resonance (NMR) and electron spin resonance (ESR) are more appropriate for a dynamic structure, in which both the detailed molecular motion of the components and their average distance of interaction can, in principle, be defined. The underlying assumption in this approach is that the assembly of the components into the membrane structure imposes mutual steric restrictions on the components which will be expressed as a characteristic pattern of molecular motion. Since there is also good evidence that functional proteins in a number of membranes have precise lipid requirements, it would be expected that functional membrane proteins would impose characteristic dynamic patterns on the lipids with which they interact.