Lipid composition of organelles from germinating castor bean endosperm

Glyoxysome, endoplasmic reticulum, mitochondria, and proplastid fractions were isolated from endosperm of castor beans (Ricinus communis) germinated for 5 days at 30 C. Samples from sucrose density gradients were diluted with 0.15 m KCI and the membranes pelleted. Lipid extracts of these membranes were analyzed for phosphoglyceride, acyl lipid, and sterol content. The endoplasmic reticulum contains 1.24 mumol of phosphoglyceride per mg of protein; the mitochondria, 0.65 mumol/mg; and the glyoxysome membranes, 0.55 mumol/mg. Phosphatidyl choline and phosphatidyl ethanolamine are the most abundant lipids in all membranes studied, accounting for 70% or more of the lipid phosphorus and 50% or more of the fatty acid. Glyoxysome membranes and endoplasmic reticulum also contain phosphatidyl inositol (respectively, 9 and 17% of the lipid phosphorus) and free fatty acids (13% of the total fatty acid in each). Compared with other organelles, mitochondrial membranes have more phosphatidyl ethanolamine relative to phosphatidyl choline and are characterized by the presence of cardiolipin, in which 80% of the fatty acid is linoleate. The relative amounts of linoleate, palmitate, oleate, stearate, and linolenate in each of the phosphotoglycerides are constant regardless of the membrane source. Stimasgasterol and beta-sitosterol are present in the membranes (1-9 nmol each/mg protein).The data provide further evidence that glyoxysome membranes are derived from the endoplasmic reticulum but at the same time indicate some differentiation.     

Lipid composition of Limulus photoreceptor membranes.

The lipid composition has been determined for rhabdomeric photoreceptor membranes of Limulus, and these data are compared with those from photoreceptor membranes of albino rats. The comparison is of interest because the membranes of these two photoreceptor cells regulate ionic transport differently during the response to illumination. 1. Phospholipid class composition of Limulus is similar, but not identical, to that of rats. The major differences are a greater percentage of sphingomyelin in Limulus and a greater percentage of phosphatidylethanolamine in the rat. 2. Ethanolamine plasmalogens, not observed in rat photoreceptor membranes, are present in Limulus photoreceptor fractions. 3. The level of cholesterol in Limulus is higher than that usually reported for vertebrate rod outer segments. 4. The predominant polyunsaturated fatty acids of Limulus photoreceptor membrane phospholipids are 20: 4(n-6) and 20: 5(n-3) with only traces of 22: 6(n-3). This is in sharp contrast with the large percentages of 22: 6(n-3) found in rat photoreceptors. 5. The fatty acid distributions of both membrane systems are highly unsaturated, but the ratio of (n-3) to (n-6) polyunsaturates is only 1.7 for Limulus as compared to 4.6 for rat.     

Lipid composition of photoreceptor membranes from goldfish retinas

Isolation and biochemical characterization of goldfish retinal photoreceptor outer segment membranes are described. The lipid fraction is composed primarily of phospholipids (68 mol%) with substantial amounts of neutral lipids (32 mol%). Sterols account for only about 2 wt% of the membranes (about 9 mol% of the total lipids). The phospholipid class composition and fatty acid composition are similar to those of other vertebrate photoreceptor membranes. Two novel findings were the high levels of free fatty acids (21 mol% of the total lipids, primarily palmitic and docosahexaenoic acids) and the presence of relatively significant amounts of a C-32 diacylglycerol molecular species.     

Lipid composition of plasma membranes from human leukemic lymphocytes.

The specific activity of adenosine 5'-monophosphatase and the concentrations of cholesterol, glucosylceramide, lactosylceramide, and phospholipids were compared in the whole homogenates and in plasma membrane fractions in four preparations of human leukemic lymphocytes taken over a 1-yr period from a patient with chronic lymphocytic leukemia. There was a 69.5-fold enrichment of the specific activity of adenosine 5'-monophosphatase in plasma membrane fractions. This enzyme appeared to be the best plasma membrane marker of all compounds studied. The increase in lactosylceramide concentration in the plasma membranes was 34.4-fold. It was significantly higher than that of glucosylceramide. The enrichment of glucosylceramide in the plasma membranes was similar to that of cholesterol and total phospholipids. The pattern of individual phospholipids in the plasma membrane fraction, as compared with the whole homogenate, was characterized by a decrease in phosphatidylcholine and an increase in sphingomyelin.     

Lipid composition of thylakoid membranes of cadmium treated wheat seedlings.

Cadmium (200 ppm) applied through the rooting medium to 30-day-old wheat plants decreased chlorophyll content, net CO2 exchanges and PSII activity by 34, 54 and 43% respectively. Thylakoid total lipids, total glycolipids, total phospholipids and total neutral lipids decreased by 22, 23, 12 and 25%, respectively, under cadmium treatment. Thylakoid membrane glycolipids had three major constituents, viz. monogalactosyl diacylglycerol, digalactosyl diacylglycerol and sulphoquinovosyl diacylglycerol. Monogalactosyl diacylglycerol and digalactosyl diacylglycerol contents decreased by 32 and 27%, respectively, under cadmium. Cadmium application also decreased the concentration of phosphatidyl glycerol and phosphatidyl choline to the extent of about 57 and 31%, respectively. On the other hand, phosphatidic acid and free fatty acids content showed an increase. These compositional changes in thylakoid membranes might be responsible for reduced PSII activity and rate of photosynthesis as observed under cadmium treatment.     

Lipid composition determines interaction of liposome membranes with Pluronic L61

Triblock copolymers of ethylene oxide (EO) and propylene oxide (PO) of EO(n/2)PO(m)EO(n/2) type (Pluronics) demonstrate a variety of biological effects that are mainly due to their interaction with cell membranes. Previously, we have shown that Pluronics can bind to artificial lipid membranes and enhance accumulation of the anti-tumor drug doxorubicin (DOX) inside the pH-gradient liposomes and transmembrane migration (flip-flop) of NBD-labeled phosphatidylethanolamine in the liposomes composed from one component-lecithin. Here, we describe the effects caused by insertion of other natural lipids in lecithin liposomes and the significance of the lipid composition for interaction of Pluronic L61 with the membrane. We used binary liposomes consisting of lecithin and one of the following lipids: cholesterol, phosphatidylethanolamine, ganglioside GM1, sphingomyelin, cardiolipin or phosphatidic acid. The influence of the additives on (1) membrane microviscosity; (2) binding of Pluronic L61; (3) the copolymer effect on lipid flip-flop and membrane permeability towards DOX was studied. The results showed that insertion of sphingomyelin and cardiolipin did not influence membrane microviscosity and effects of Pluronic on the membrane permeability. Addition of phosphatidic acid led to a decrease in microviscosity of the bilayer and provoked its destabilization by the copolymer. On the contrary, cholesterol increased microviscosity of the membrane and decreased binding of Pluronic and its capacity to enhance flip-flop and DOX accumulation. Analogous tendencies were revealed upon incorporation of egg phosphatidylethanolamine or bovine brain ganglioside GM1. Thus, a reverse dependence between the microviscosity of membranes and their sensitivity to Pluronic effects was demonstrated. The described data may be relevant to mechanisms of Pluronic L61 interaction with normal and tumor cells.     

Lipid composition and fluidity of rat enterocyte basolateral membranes regional differences

The lipid composition and fluidity of basolateral membranes prepared from the mucosa of the proximal, middle and distal thirds of the rat small intestine were determined. Fluidity, as assessed by the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene and a series of anthroyloxy fatty acid derivatives, is decreased in the distal third as compared to the proximal segments. This pattern is similar to that described previously for microvillus membranes. The decrease in fluidity of the distal as compared to the proximal membranes results from an increase in cholesterol content, cholesterol/phospholipid molar ratio and degree of saturation of the fatty acid residues. In the middle and distal thirds of the gut, the degree of saturation of the fatty acid residues is higher in microvillus as compared to basolateral membranes, accounting in part for the characteristically lower fluidity of the luminal membranes. The specific activity of the basolateral membrane (Na⁺ + K⁺)-dependent adenosine triphosphatase is significantly lower in the distal as compared to the proximal and middle thirds of the intestinal mucosa. Studies of the binding of [³H]ouabain indicate that this pattern results from fewer enzyme sites in the distal membranes.     

Lipid order and composition of synaptic membranes in experimental diabetes mellitus

The effect of diabetes in rats on lipid composition and order of synaptosomal membranes (SM) was determined in streptozotocin-induced diabetic rats after 6 weeks of chronic hyperglycemia. The cholesterol content was slightly, but not significantly, higher in diabetic SM (0.287±0.042 vs. 0.209±0.061 mol/mg protein). The phospholipid concentration in diabetic SM was significantly increased (0.515±0.042 vs. 0.305±0.041 mol/mg protein;P<0.005). Neither the molar ratios of cholesterol to phospholipids in the SM nor the fatty acid composition of the SM was significantly altered with diabetes. Diabetes did not affect membrane order or the thermotropic transition temperature of the SM as determined fluorometrically. On the other hand, the SM of diabetic rats had significantly increased concentration of lipid peroxidation products, namely conjugated dienes (the calculated O.D./mol phospholipids was 11.56±1.83 in controls and 19.95 ±4.1 in diabetic ratsP<0.01). Despite the accumulation of lipid peroxidation byproducts in SM of diabetic rats the overall membrane order and the cholesterol to phospholipid molar ratio do not appear to be significantly altered.     

Lipid composition of plasma membranes isolated from sunflower seedlings grown under water-stress

Plasma membranes were isolated by aqueous two-phase-partitioning from sunflower ( Helianthus annuus cv. Isabel) seedlings grown both under field irrigation and dryland conditions. Water-stressed plants showed a decrease in the leaf water potential and in the osmotic potential at full turgor, with the turgor pressure remaining at positive values. Dryland conditions also induced a reduction in the bulk modulus of elasticity. Plasma membranes of irrigated plants were characterized by high contents of phospholipids (68% of total lipids), free sterols (15. 7%) and glycolipids (9. 1%), mainly glycosphingolipids and steryl glycosides. Diacylglycerols, triacylglycerols and free fatty acids were also present. The major phospholipids were phosphatidylcholine and phosphatidylethanolamine with smaller amounts of phosphatidylinositol and phosphatidylglycerol. Following water stress, the plasma membranes showed a reduction of about 24 and 31% in total lipids and phospholipids, respectively. Also the amounts of glycolipids and diacylglycerols decreased significantly upon water stress. There was no change in free fatty acids, however, and triacylglycerols and free sterols increased. As a consequence, the free sterol to phospholipid molar ratio increased from 0. 4 to 0. 7 under water deficit conditions. The ratio of phosphatidylcholine to phosphatidylethanolamine increased from 1. 1 (control plants) to 1. 6 (water-stressed plants), while phosphatidic acid rose to 4% of total phospholipids. Dehydration did not result in any substantial change in the unsaturation level of the individual lipid classes, however. The results show that dryland conditions resulted in a marked alteration in the lipid composition of the sunflower leaf plasma membrane     

Lipid composition and lateral diffusion in plasma membranes of teratocarcinoma-derived cell lines

We measured lipid lateral diffusion rates for a series of teratocarcinoma-derived and embryo-derived cell lines, using the technique of fluorescence photo-bleaching recovery with a fluorescent lipid probe, C₁₆dil. The probe diffuses more rapidly in plasma membranes of embryonal carcinoma cells than in plasma membranes of teratocarcinoma-derived endodermal cell lines. When embryonal carcinoma cells are induced to differentiate by treatment with retinoic acid, diffusion constants of C₁₆dil are reduced to levels typical of endoderm. These changes are paralleled by differences in membrane cholesterol content; membrane free cholesterol levels in embyronal carcinoma lines are approximately half those found in endodermal lines, and are markedly increased upon retinoic-acid-induced differentiation.