Showing papers on "Membrane lipids published in 1972"

Asymmetrical lipid bilayer structure for biological membranes.

Abstract: IT is generally accepted that the matrix of cellular membranes is a bimolecular leaflet of phospholipid molecules in which the phospholipids are oriented so that their polar heads reside on the outer surfaces of the bilayer, in contact with the aqueous environment, the interior of the sandwich being composed of hydrophobic lipid chains1–5. To this basic structure proteins cholesterol, glycolipids and other molecules are usually inserted in such a way as to confer on the bilayer the functional properties appropriate for the particular membrane.

Isolation of the Insulin Receptor of Liver and Fat-Cell Membranes

Abstract: Extraction of liver and fat-cell membranes with the nonionic detergent Triton X-100 prevents specific binding of 125I-labeled insulin to these membranes. This loss of binding to particulate material is quantitatively recovered in a high-speed (300,000 × g, 2 hr) supernatant of the extract. Specific and reversible insulin binding to soluble proteins is readily demonstrable by gel filtration. A simple and sensitive assay for detection of specific macromolecule-insulin complexes has been developed based on the selective precipitation of the complex by polyethylene glycol. Extraction of membrane lipids with organic solvents or by phospholipase digestion does not impair the subsequent extraction of the insulin-binding protein with detergent. Binding of insulin to the soluble protein is a saturable and dissociable process having a dissociation constant of about 100 nM. Derivatives of insulin compete for binding in direct proportion to their biological activity; other peptide hormones are without effect. The quantitative features of the detergent extractions and the specific insulin-binding properties of the material so obtained indicate that the protein solubilized is the biologically significant insulin receptor, whose insulin-binding function is essentially unaltered.

Comparative Aspects of Bacterial Lipids

Abstract: Publisher Summary This chapter deals with the comparative aspects of bacterial lipids The chapter attempts to outline their differences, to describe the biosynthetic systems—the presence or absence of which lead to the observed compositions, and to assess the significance of these differcnces Bacterial lipids have been discussed extensively in monographs Research on bacterial lipids focuses on such questions as their location in functional membrane units, the relationship of individual lipid species to vitrous enzymes, multi-enzyme complexes, and transport systems The regulation of membrane–lipid biosynthesis at the enzyme level is receiving more attention in bacteria, and the isolation of a variety of mutants with lesions in the synthesis of lipids promises to lead to a better understanding of the genetics and control of lipid biosynthesis It has long been recognized that cell diversity among the bacteria tends to increase toward the periphery of the cell, and the membrane lipids clearly offer a fertile ground for the study of comparitive biochemistry

Lipids of membranes and of the cell envelope in heterocysts of a blue-green alga.

Abstract: Heterocysts of Anabaena cylindrica, isolated rapidly in the cold, were found—in contrast to earlier reports—to contain all of the same lipids and lipophilic pigments, and in about the same proportions, as vegetative cells. In broken filaments and in heterocysts damaged during isolation, the membrane lipids and certain pigments (myxoxanthophyll and an unidentified red pigment) break down rapidly. The glycolipids specific to heterocyst-forming blue-green algae are localized in the laminated layer of the heterocyst envelope. A possible role of the laminated layer is discussed.

The Composition of Biological Membranes

Abstract: The main components of biological membranes are proteins, lipids, and carbohydrates in variable proportions. Carbohydrates account for less than 10% of the mass of most membranes and are generally bound either to the lipid or protein components. Myelin has few functions and is made up almost entirely of lipids. In plasma membranes, the weight ratio of lipid to protein is close to 1; in several specialized membranes (ie, mitochondrion and bacterial cells) this ratio is near 2 or 3. Thus, there appears to be a correlation between the number of activities performed by and the amount of protein in a membrane. The main membrane lipids are phospholipids, cholesterol, and glycolipids. Glycolipids seem to be cell antigens, and they, together with glycoproteins, may determine surface characteristics of a cell which distinguish it from other cells. Approximately ten polypeptide chains of different molecular weights make up most of the mass of protein in plasma membranes.

Vitamin e protection of membrane lipids during electron transport functions

Abstract: Beloff-Chain and colleagues,' while investigating electron transport associated with TPNH oxidation in order to determine whether the oxygen uptake was accompanied by phosphorylation of ADP, found that such phosphorylation did not take place, but they did find a stoichiometric excess in the amount of oxygen consumed. In examining this phenomenon, Hochstein and colleagues2 observed that during the oxidation of TPNH by liver microsomes in the presence of ADP and a small quantity of iron, a substance was formed having properties of malondialdehyde; this indicated that oxidative degradation of polyunsaturated lipids was occurring. The investigations of Orrenius and colleagues3 and Wills4 indicate that the system involves part or all of the drug-metabolizing system. Because the concentrations of TPNH, ADP, and iron required to promote the maximum rate of the microsomal reaction are within the physiological levels existing in the cytosol of the liver cell,5 we undertook to investigate the nature of this phenomenon. The objective of these studies was to determine to what extent membrane-bound electron transport systems involving large free energy changes may promote degradation of lipids in the membranes and associated impairment of enzymic activity. In the course of these studies it was established that dietary a-tocopherol has a regulatory effect on this phenomenon. The results to be presentedindicate that TPNH-dependent electron transport is associated in both microsomes and mitochondria with the production of a highly transient factor possessing the properties of a free radical. This factor apparently promotes the peroxidative chain scission of the polyunsaturated fatty acid (PUFA) moieties of phospholipids in the rnicrosomal and mitochondria1 membranes. I t was also shown that during this process microsomal a-tocopherol is converted to a polar compound and that in mitochondria there is loss of the capacity to carry out oxidation of Krebs cycle intermediates and the associated phosphorylation. This capacity can be restored by the addition of cytochrome c to the assay systems.

MEMBRANE SYNTHESIS IN BACILLUS SUBTILIS III. The Morphological Localization of the Sites of Membrane Synthesis

Abstract: The results of several lines of investigation indicate that membrane growth in Bacillus subtilis does not occur at one or a small number of discrete zones. No indications of large regions of membrane conservation were observed. Kinetic labeling experiments of mesosomal and plasma membrane lipids indicate that the mesosomal lipids are not precursors of the plasma membrane lipids. Density shift experiments, in which the changes in buoyant density of membranes were studied after growth in deuterated media, showed no indication of large zones of conservation during membrane growth. Radioautography of thin sections of cells pulse labeled with tritiated glycerol showed no indication of specific zones of lipid synthesis. The consequences of these results for models of cell growth and division are discussed.

The "free" lipids of two different strains of hydrogen-oxidizing bacteria in relation to their growth phases.

Abstract: Two strains of hydrogen-oxidizing bacteria were used: Hydrogenomonas eutropha strain H16 and strain 11/x The former is a gram-negative flagellated rod and has been relatively well known with respect to its morphological, physiological, and biochemical properties The latter is a gram-positive, non spore-forming, motile small rod the definite classification of which is unknown as yet Both strains were grown chemolithotrophically in submerged culture with a limited nitrogen-source and supplied with a gas mixture of H2, O2, and CO2 The lipid composition of the bacteria was determined at the end of the exponential phase (I), at the storage phase (II), and after reutilization of storage material (III) Along with the accumulation of poly(3-hydroxybutyric acid) as the major storage material in strain H16 the amount of other lipids was shown to increase 18-fold at phase II and to decrease at phase III There is little or no change in the lipid pattern in various growth phases It is suggested that the 18-fold increase of the latter lipids during phase II is due to the synthesis of membrane lipids that are required for the formation of membranes surrounding the intra-cellular granules of accumulating poly(3-hydroxybutyric acid) In strain 11/x the amount of lipids increases 7 times along with an equal increase of carbohydrates at phase II The majority of accumulated lipids consists of triglycerides free of significant amounts of unusual acyl group It is suggested that there is a true storage of triglycerides that are reutilized during phase III The lipid pattern of strain H16 is characterized by a high proportion of “strongly bound lipids” that consist predominantly of phospholipids Characteristic lipid components are phosphatidylethanolamine, phosphatidylglycerol, and diphosphatidylglycerol, while coenzyme Q8 (041 μmol/g bacterial dry weight) has been found among the neutral lipids A C17 cyclopropane acid (probably cis-9,10-methylene hexadecanoic acid) is present in all saponifiable lipids The lipid pattern of strain 11/x is characterized by a high proportion of “loosely bound lipids” that consist predominantly of neutral lipids, particularly of triglycerides Among the polar lipids, diphosphatidylglycerol and phosphoinositides are most abundant, and several unknown phospholipids are also present No cyclopropane fatty acid has been found The possible use of strain 11/x as a source of nutritional fat is discussed

The absence of lipid peroxidation in human red cells exposed to acetylphenylhydrazine.

Abstract: Summary. The membrane lipids from human red cells which had been treated with acetylphenylhydrazine were examined for evidence of autoxidation. Malonyldialdehyde production was measured and the lipids were extracted and examined by thin-layer chromatography. No lipid autoxidation was detected by either method, even when the cellular haemoglobin was considerably oxidized. In addition, the susceptibility of red-cell lipids to autoxidation by hydrogen peroxide did not increase if the cells were prcincubated with APH. The significance of these results is discussed in relation to the mechanism of haemolysis in Heinz-body haemolytic anaemias.

Thermophilic fungi: IV. The lipid composition of six species

Abstract: The lipid composition of six thermophilic fungi (Myriococcum albomyces, Mucor miehei, Papulaspora thermophila, Rhizopus sp.,Thielavia thermophila (+)Thielavia thermophila (−), andTorula thermophila) was examined. The relative per cent total lipids (4.9–26.3%), neutral lipids (55.5–88.3%), polar lipids (11.7–44.6%) and the fatty acid profile of each lipid fraction was determined. The predominant fatty acids were 16∶0, 18∶0 and 18∶2, and lesser amounts of 12∶0, 14∶0, 15∶0, 16∶1, 16∶2, 17∶0 and 18∶3 were present. The total lipids contained an average of 0.96 double bonds per mole fatty acid (unsaturation index [USI]) the neutral lipids 0.86 USI and the polar lipids 0.84 USI, excluding the values forTorula thermophila. These data show a high degree of saturation and are consistent with data reported for other fungal thermophiles.Torula thermophila possessed abnormally high USI values (1.15–1.50) and was cultured at three different temperatures (25, 45 and 51 C). As the culture temperature ofTorula thermophila increased, the USI decreased. The USI of the polar lipids ofTorula thermophila at 25, 45 and 51 C were 1.50, 1.28 and 1.11, respectively. Thus the membrane lipids of this fungus appear unusual for a thermophile.

The Structure of Erythrocyte Membranes

Abstract: The membrane proteins of beef erythrocyte ghosts have been fractionated on the basis of their different interactions with lipid. The individual proteins in each fraction have then been characterized by polyacrylamide gel electrophoresis. Fractions I and II, which were solubilized from the membrane by distilled water and 1.2 M NaCl, respectively, amounted to 46% of the total membrane protein and included virtually all the polypeptide-chains with molecular weights greater than 200000. These proteins must be linked to the membrane by predominantly ionic interactions, indicating that they are extrinsic proteins of the erythrocyte membrane. A considerable proportion of membrane protein (fraction III) was not liberated by distilled water or 1.2 M NaCl but could be separated from lipids by sodium dodecylsulphate, a reagent which disrupts hydrophobic interactions. 10 different polypeptides were identified in this fraction, including four glycoproteins. One polypeptide of molecular weight 87000 accounted for about half of the protein-staining components. The proteins in this fraction are likely to be intrinsic membrane proteins which penetrate deeply into the lipid bilayer of the erythrocyte membrane.

Effects of ethanol on membrane lipids. II. Changes in the content and metabolism of aldehydogenic lipids in mouse total liver, mitochondria and microsomes.

Abstract: 1. 1. The free fatty aldehyde content of mouse liver microsomes increased in mice fed ethanol. 2. 2. Ethanol decreased the percentage of plasmalogen in several microsomal phospholipids. Similar effects were observed in mitochondria and total liver phospholipids, although, in some instances, increases in the percentage of plasmalogen occurred. 3. 3. A plasmalogenase was found to be stimulated in the mitochondria and microsomes of the alcohol group. 4. 4. Alcohol affected the metabolism of radio-labeled plasmalogen, 1- 14 C-palmitaldehyde and 1 14 C-cetyl alcohol. The effect could be related to an increased NADH 2 /NAD ratio. A metabolic pathway to account for the observed results is presented.

Lipids of the cell plasma membrane.

Abstract: Cellular interfaces are Known to contain large quantities of lipids The concept of the molecular organization of these membranes is still in a state of flux and many attempts are being made to evaluate more precisely the contribution of lipids to the properties of the biological interfaces Recent advances in separation and analytical techniques have made it possible to isolate pure membrane preparations and to determine their detailed lipid composition (48, 57] The emphasis of this paper will be placed on the plasma membrane, but let it be stated that the plasma membrane is not the putermost envelope for all freely living cells as bacteria, yeast and fungi, though it regulates predominantly the permeability of low-molecular substances Also the interaction of the intracellular membranes with the function of the cell membrane has to be mentioned The structure and function of the plasma membrane and other cell membranes have been considered in many papers (eg 29, 33, 37, 57)