Showing papers on "Membrane lipids published in 1969"

Calorimetric evidence for the liquid-crystalline state of lipids in a biomembrane

Abstract: Both membranes of Mycoplasma laidlawii and water dispersions of protein-free membrane lipids exhibit thermal phase transitions that can be detected by differential scanning calorimetry. The transition temperatures are lowered by increased unsaturation in the fatty acid residues, but in each case they are the same for membranes and lipids. The transitions resemble those observed for synthetic lipids in the lamellar phase in water, which arise from melting of the hydrocarbon chains within the phospholipid bilayers. Such melts are cooperative phenomena and would be greatly perturbed by apolar binding to protein. Thus the identity of membrane and lipid transition temperatures suggests that in the membranes, as in water, the lipids are in the bilayer conformation in which the hydrocarbon chains associate with each other rather than with proteins. Observations of morphological changes indicate that osmotic imbalance occurs when the membrane transition temperature exceeds the growth temperature, and that for transport processes to function properly the hydrocarbon chains must be in a liquid-like state.

Discrete Conductance Fluctuations in Lipid Bilayer Protein Membranes

Abstract: Discrete fluctuations in conductance of lipid bilayer membranes may be observed during the initial stages of membrane interaction with EIM ("excitability inducing material"), during destruction of the EIM conductance by proteolysis, and during the potential-dependent transitions between low and high conductance states in the "excitable" membranes. The discrete conductance steps observed during the initial reaction of EIM with the lipid membranes are remarkably uniform, even in membranes of widely varying lipid composition. They range only from 2 to 6 x 10-10 ohm-1 and average 4 x 10-10 ohm-1. Steps found during destruction of the EIM conductance by proteolysis are somewhat smaller. The transition between high conductance and low conductance states may involve steps as small as 0.5 x 10-10 ohm-1. These phenomena are consistent with the formation of a stable protein bridge across the lipid membrane to provide a polar channel for the transport of cations. T6he uniform conductance fluctuations observed during the formation of these macromolecular channels may indicate that the ions in a conductive channel, in its open state, are largely protected from the influence of the polar groups of the membrane lipids. Potential-dependent changes in conductance may be due to configurational or positional changes in the protein channel. Differences in lipid-lipid and lipid-macromolecule interactions may account for the variations in switching kinetics in various membrane systems.

Patterns of non-electrolyte permeability.

Abstract: Reflexion coefficients (σ’s) for epithelial cells of rabbit gall-bladder for 206 non-electrolytes have been measured and analysed. In general, σ’s decrease from 1.0 to 0 with increasing lipid :water partition coefficients, so that the intermolecular forces governing permeation of most non-electrolytes are the same as those governing partition between a bulk lipid phase and water. The two classes of deviations to this pattern are related to the specific structure of cell membranes. First, highly branched molecules have higher σ’s (permeate more slowly) than expected from partition coefficients, an effect attributed to an isotropy of membrane lipids. Secondly, the smallest, most lipid-insoluble molecules have lower σ’s (permeate more readily) than expected, and are also anomalous in that: effects of changes in their structure on or disobey Overton’s rules; the inverse relation between or and temperature is less steep for them than for other so lutes; and their σ’s are little affected by decreases in pH which increase σ’s of other solutes. These anomalies are interpreted to mean that small polar solutes in transit through the membrane interact minimally or not at all with hydrocarbon tails of membrane lipids, but in stead follow a route formed by localized concentrations of membrane polar groups associated with ‘frozen’ water molecules, where the coupling phenomena between permeating water, ions, and small polar-electrolytes observed in cell membranes may also occur.

Mycoplasma Membrane Lipids: Variations in Fatty Acid Composition

Abstract: The fatty acid composition of the membrane polar lipids of Mycoplasma laidlawii B can be dramatically altered. These variations reslut in characteristic morphological chlanges, and in most cases the cells remain viable. This organism should provide a useful system for clarifying the role of fatty acyl chains in biological membranes.

The role of membrane lipids in the survival of red cells in hereditary spherocytosis.

Abstract: A B S T R A C T Red cells in hereditary spherocytosis (HS) have a decreased ratio of membrane surface area to cell volume and therefore a spheroidal shape. This abnormality in shape predisposes them to pooling and destruction in the spleen. Although splenectomy prevents hemolysis in HS, the red cell defect, as manifested by spheroidicity, increased autohemolysis, excesive permeability to sodium, and hypermetabolism, persists. The role of membrane lipids in these manifestations in vitro and in cell survival in vivo was examined. Before splencetomy, and in spite of the presence of a young cell population, the cholesterol and phospholipid content of HS red cells is decreased. After splenectomy lipid values are similar to those obtained in normal subjects with spleens. However, after splenectomy for conditions other than HS the lipid content of red cells is greater than normal. Thus, when compared with the red cells of patients without HS who have also undergone splenectomy, HS cells after splenectomy are deficient in both cholesterol and phospholipid. Obstructive jaundice causes an increase in membrane lipid, primarily cholesterol, and a decrease in the osmotic fragility of normal red cells. When HS red cells are transfused into patients with obstructive jaundice they also become less osmotically fragile. Moreover, when incubated in obstructive jaundice serum, they gain cholesterol. This acquisition of membrane lipid in vitro does

Membrane lipids and the conformations of membrane proteins.

Abstract: The general relations between protein conformation and the optical activity of peptide chromophores are outlined and applied to the analysis of the optical rotatory dispersion and circular dichroism of the plasma membranes of human erythrocytes and Ehrlich ascites carcinoma cells It is concluded that the proteins of these membranes are "globular" and that they have considerable helical content The spectroscopic consequences of perturbing the membranes with phospholipase C, phospholipase A, lysolecithin, and sodium dodecyl sulfate are examined in the light of the effects of these agents upon certain enzymatic and physical properties of the membranes and upon their proton magnetic resonance spectra The data suggest that the architecture of membrane proteins is strongly dependent upon apolar lipid-protein and/or lipid-sensitive protein-protein interactions

Surface Area per Lipid Molecule in the Intact Membrane of the Human Red Cell

Abstract: MODELS for the structure of the red cell membrane vary according to the assessment of the area occupied by the lipids in the cell surface. In 1925, Gorter and Grendel1 found the area of a monomolecular film of extracted lipids at an air–water interface to be twice that of the cell surface area and postulated a lipid bilayer in the membrane. Dervichian and Macheboeuf2 used similar techniques and obtained a ratio of 1 : 1. Bar et al.3 found that the ratio depends on the surface pressure used in compressing the film: higher pressures lead to a lower area per lipid molecule and hence to a lower ratio of lipid area to membrane area, and lower pressures lead to a higher ratio. There is, however, little basis for deciding which pressure best represents the situation of the lipids in the intact membrane.

Immunological Analysis of Mycoplasma Membranes

Abstract: The antigens responsible for the production of antibodies to Mycoplasma laidlawii and M. gallisepticum causing growth and metabolic inhibition of these organisms were localized in the cell membrane. Various membrane fractions were tested for serological activity. Membrane lipids were completely or almost completely inactive, whereas several preparations of defatted membrane proteins retained some serological activity, shown by their ability to stimulate metabolic inhibition antibody in rabbits and to adsorb metabolic inhibition antibody and form precipitation lines with an antiserum to the membrane. When the membranes were heated to 65 C for 1 hr, they virtually lost their ability to adsorb metabolic inhibition antibody, which suggests that the antigenic determinants are proteins. Serological activity was retained in reaggregated membranes obtained by dialysis against Mg2+ of membranes solubilized in sodium dodecyl sulfate. The amount of solubilized membrane protein and lipid incorporated into the reaggregated membranes could be regulated by varying the Mg2+ concentration. As the serological tests indicated that the various membrane antigens were selectively incorporated into the different reaggregated membranes, the use of controlled reaggregation of solubilized membranes is suggested as a new tool for the fractionation and antigenic analysis of membrane proteins.

Myxovirus Envelope Proteins: A Directing Influence on the Fatty Acids of Membrane Lipids

Abstract: Acyl chain compositions of the lipids of three strains of influenza virus show differences not anticipated from current theories of myxovirus assembly. Fatty acids of viruses with antigenically related envelope proteins show greater resemblance than those of an unrelated strain, which suggests that these proteins influence the composition of membrane lipids at the site of viral release.

Carotenoid bilayer lipid membrane model for the visual receptor.

Abstract: INTEREST in black or bilayer membranes (BLM) of about bimolecular thickness separating two aqueous solutions has grown rapidly since the methods for their formation were discovered1,2. Their attractiveness as a model system lies in the dimensional, electrical, permeability and “excitability” characteristics which they possess and which correspond to those of biological membranes. BLM have been used as models for the plasma membrane, for nerve membrane and, more recently, for the mitochondrial membrane3; and in a modified BLM system the active transport of ions seems to have been demon strated4. Other interesting findings have been light-induced phenomena in reconstituted chloroplast BLM5. We now report a type of black lipid membranes containing carotenoid pigments (“carotenoid BLM”) which exhibit photoelectric responses not unlike those found in vertebrate retina6.

Die “freien” Lipide aus Brucella abortus Bang

Abstract: Brucella abortus Bang (strain Scherle II and strain 1119) was grown on solid media and harvested after approximately 70 h. The “free” lipids were prepared. The bacteria contained 3.3% and 4.5% free lipids by dry weight of strain Scherle II and strain 1119, respectively. The free lipids were fractionated by acetone. The acetone-insoluble lipids (85.3% and 77.3% of the free lipids by weight of strain Scherle II and strain 1119, respectively) contained 2.85% and 3.03% P, respectively. They were analyzed by thin-layer chromatography. The acetone-insoluble lipids of strain Scherle II were fractionated by column chromatography on silicic acid under thin-layer chromatographic control. Subsequently certain fractions were fractionated by further column chromatographic procedures on silicic acid and/or DEAE cellulose yielding 6 phosphatides in pure states: lecithin, phosphatidyl-N-dimethylethanolamine, phosphatidyl-N-methylethanolamine, phosphatidylethanolamine, phosphatidylglycerol and cardiolipin. These phosphatides were identified by analyses of their deacylation products. The relative amounts of these phosphatides were determined. Lecithin turned out to be the major constituent (34.5% in strain Scherle II, 37.3% in strain 1119, on a molar basis with respect to phosphorus). Strain Scherle II probably also contained phosphatidylserine and an inositol phosphatide in minor amounts. The 6 phosphatides isolated were completely susceptible to phospholipase A from snake venom. Thus, the phosphatides existed in the L-configuration. By gas-liquid chromatography of the fatty acids split off by the action of snake venom and of the fatty acids of the remaining lysophosphatides, we determined the positional distribution of the component fatty acids. We found C19 cyclopropane fatty acids to be located preferentially at the 2-positions of the 6 phosphatides isolated, while the 1-positions were preferentially occupied by different fatty acids which we tentatively determined as hydroxy acids. The lipids of Brucella abortus display an exceptional case in that they contain lecithin as their major component. In this and some other respects they resemble the lipid pattern of Agrobacterium and of certain photosynthesizing bacteria. Because of the absence of polyenoic fatty acids in bacterial lipids it is suggested that cyclopropane fatty acids play a similar role in bacterial membrane lipids as polyenoic acids do in membrane lipids of higher organisms. However, since it has been suggested that the membrane proteins have special binding sites for different apolar groups of phosphatides, it has to be supposed that the properties of bacterial membranes differ markedly from those of higher organisms.

Photoconductivity in Black Lipid and Thin Lipid Membranes

Abstract: TIEN has recently reported1,2 that black or bilayer lipid membranes and thin lipid membranes containing photo-synthetic pigments such as chlorophylls and xanthophylls possess photoconductive properties. He illuminated one side of the membrane from a source of fixed intensity and observed the changes in current flowing through, and in potential across, the membrane on illumination. The source was a 500 W tungsten lamp with a lens and heat filter, but the extent to which radiation heating of the membrane was reduced by the filter is uncertain. The thermal contribution in the reported photo effects is therefore also uncertain.

Myelin metabolism in vitro in experimental allergic encephalomyelitis.

Abstract: — Spinal cord slices from rats in different stages of allergic encephalomyelitis (EAE) were incubated with [U-14C]glucose. Normal rats and rats injected with Freund's adjuvant served as controls. The slices were fractionated by a discontinuous sucrose gradient into purified myelin and a heavy membrane residue, the lipids and proteins were extracted, and their specific activities were determined. Uptake of 14C into myelin lipids was depressed in the rats with acute EAE, while an increase was shown in myelin protein and heavy membrane lipids and proteins. The increased synthesis in non-myelin fractions was ascribed to invasion of metabolically active cells. The depression in myelin lipid synthesis occurred early in the disease before lesions appeared or the inflammatory reaction became widespread. Myelin from guinea pigs with acute EAE resulting from injection of a purified basic protein also showed a depression of uptake in both lipids and proteins. It is suggested that a metabolic insult as a result of the immunological process is dealt the oligodendroglial cells early in the course of the disease which leads to a weakening of the myelin sheath and subsequent phagocytosis of myelin.