Fluidity and lipid composition of oat and rye shoot plasma membrane: effect of sterol perturbation by xenobiotics

Oat and rye plants were treated with either tetcyclacis (an experimental plant growth regulator), nuarimol (a fungicide) or gamma-ketotriazole (an experimental herbicide). These treatments reduced shoot growth and changed the lipid composition of the shoot plasma membranes. In oat, both tetcyclacis and nuarimol treatments increased plasma membrane cholesterol and increased the phosphatidylethanolamine/phosphatidylcholine (PE/PC) ratio, whereas gamma-ketotriazole treatment reduced cholesterol and the PE/PC ratio. In rye, all treatments reduced the PE/PC ratio. Generally, the sterol/phospholipid ratio was less in oat than in rye but the cholesterol/phospholipid ratio was greater. With all treatments in oat and rye, increases were observed in unsaturation of the phospholipid acyl chains. The fluidity of membranes was measured by steady-state fluorescence polarisation of the probe diphenylhexatriene; oat membranes were more fluid than rye. Membrane fluidity was greater in plasma membranes from plants treated with the xenobiotics than the controls. The results are discussed in the context of the effect of plasma membrane lipid composition on membrane fluidity, and it is concluded that there appears to be no overall simple relationship between membrane lipid composition and fluidity that holds for all treatments in both species.     

Red Blood Cell Membrane Fluidity in the Etiology of Multiple Sclerosis

Organisms adjust the order, or fluidity, of their cellular membranes in response to changes in their physiochemical environment by adjusting the lipid composition of their membranes. We investigated membrane fluidity using the phospholipid, fatty acid and cholesterol content of red blood cells (RBCs) from multiple sclerosis (MS) patients and correlated this with C-reactive protein (CRP) as well as with the severity of neurological outcome as measured by the Kurtzke Expanded Disability Status Scale (EDSS) and its Functional System Scores. The study group consisted of 31 patients with MS and 30 healthy control subjects. Phospholipids were determined using a colorimetric assay, fatty acids by gas chromatography, cholesterol by an enzymatic assay and CRP by a Beckman nephelometer. Cell membrane fluidity was calculated according to previously established formulae. RBC membrane fluidity as measured by the saturated to polyunsaturated fatty acid ratio was higher in patients than in controls (P = 0.04). The phosphatidylethanolamine saturated to polyunsaturated fatty acid ratio showed highly significant positive correlations with the EDSS and CRP < 5 μg/ml. CRP showed significant inverse correlations with the saturated nature but positive correlations with the ordered-crystalline-phase to liquid-crystalline-phase lipid ratio. In this study we show that membrane fluidity as measured by the relationship between membrane fatty acids, phospholipids and cholesterol is closely interrelated with inflammation and disease outcome in patients with MS. In conclusion, our findings suggest that the membrane lipid composition of patients with MS and, consequently, membrane fluidity are altered, which seems to be influenced by the inflammatory status.     

Influence of Phospholipid Species on Membrane Fluidity: A Meta-analysis for a Novel Phospholipid Fluidity Index

Generalized membrane lipid composition determinants of fluidity have been widely investigated, including phospholipid/cholesterol ratio and unsaturation index. Individual phospholipids differ in their physical characteristics, including their interaction with cholesterol and level of unsaturation, emphasizing the importance of examining their individual influence on membrane fluidity. Thus, the purpose of this study was to examine the dominant phospholipids of biological membranes (phosphatidylcholine, PC; phosphatidylethanolamine, PE; sphingomyelin, SM) through a meta-analysis to assess the validity of an inclusive phospholipid fluidity index (PFI = PC/(PE + SM)) as a determinant for membrane fluidity (expressed as polarization of fluorescent probe 1,6 diphenyl-1,3,5-hexatriene) in comparison to previous phospholipid ratios (PC/PE and PC/SM). The results demonstrate that all indices significantly predicted membrane fluidity at 25°C (based on 10–13 data points). In contrast, only PFI approached significance when predicting membrane fluidity at 37°C (P = 0.10 based on five points). As a result, PFI appears to be the only phospholipid index close to significantly predicting membrane fluidity at mammalian physiological temperature. Because this meta-analysis only assessed studies using mammalian membranes, future work should experimentally assess the validity of the PFI utilizing membranes from mammals and a variety of other species and tissues at their respective physiological temperatures.     

Fluidity of natural membranes and phosphatidylserine and ganglioside dispersions: Effects of local anesthetics,cholesterol and protein

The microviscosity of artificial lipid membranes and natural membranes was measured by the fluorescence polarization technique employing perylene as the probe. Lipid dispersions composed of brain gangliosides exhibited greater microviscosity than phosphatidylserine (268 cP vs 173 cP, at 25 °C). Incorporation of cholesterol (30–50%) increased the microviscosity of lipid phases by 200–500 cP. Cholesterol's effect on membrane fluidity was completely reversed by digitonin but not by amphotericin B. Incorporation of membrane proteins into lipid vesicles gave varying results. Cytochrome b₅ did not alter membrane fluidity. However, myelin proteolipid produced an apparent increase in microviscosity, but this effect might be due to partitioning of perylene between lipid and protein binding sites since the latter have a higher fluorescence anisotropy than the lipid. The local anesthetics tetracaine and butacaine increased the fluidity of lipid dispersions, natural membranes and intact ascites tumor cell membranes. The effect of the anesthetics appears to be due to an increased disordering of lipid structure. The fluidity of natural membranes at the 25 °C varied as follows:polymorphonuclear leukocytes, 335 cP; bovine brain myelin, 270 cP; human erytherocyte, 180 cP; rat liver microsomes, 95 cP; rat liver mitochondria, 90 cP. In most cases the microviscosity of natural membranes reflects their cholesterol : phospholipid ratio. The natural variations in fluidity of cellular membranes probably reflect important fuctional requirements. Similarly, the effects of some drugs which alter membrane permeability may be the result of their effects on membrane fluidity.     

Renal cortical brush-border and basolateral membranes: Cholesterol and phospholipid Composition and relative turnover

Summary A new procedure for the rapid isolation of renal cortical brush-border and basolateral membranes from the same homogenate is described. Brush-border membranes isolated using Mg²⁺-EGTA precipitation were enriched 18-fold for leucine aminopeptidase and had a recovery of 32.5%. Basolateral membrane fractions were isolated using a discontinuous sucrose gradient and showed an enrichment of 10.7-fold and recovery of 12.8% using (Na⁺, K⁺)-ATPase as a marker enzyme. Lipid analysis using two-dimensional TLC separation of phospholipids and gas liquid chromatography for cholesterol showed marked differences in the lipid composition of the brush-border and basolateral membranes. The brush-border membrane had increased sphingomyelin, phosphatidylserine, ethanolamine plasmalogens, and an increased cholesterol-to-phospholipid and sphingomyelin-to-phosphatidylcholine ratio compared to the basolateral membrane. The relative turnover of total membrane and individual phospholipid species using a double isotope ratio method was carried out. Phospholipids were labeled with either phosphorus 32 and 33 or acetate (³H, 1-¹⁴C). The relative turnover of phospholipid species and cholesterol differed strikingly. Phosphatidylcholine showed a high turnover, phosphatidylethanolamine and phosphatidylinositol had intermediate values and sphingomyelin, phosphatidylserine and cholesterol had low relative turnover rates. The order of phospholipid class relative turnover was independent of the labeled precursor used. The brush-border membrane had a significantly reduced relative turnover rate for total membrane phospholipids, sphingomyelin and cholesterol compared to the basolateral membrane. These data show marked differences in the lipid composition and relative turnover rates of the phospholipid species of the brush-border and basolateral membranes. They provide a biochemical basis for the recently reported differences in brush-border and basolateral membrane fluidity and suggest independent cellular regulation of brush-border and basolateral membrane lipids.     

Ontogeny of proximal colon basolateral membrane lipid composition and fluidity in the rabbit.

Basolateral membranes from rabbit proximal colon were prepared from isolated colonocytes throughout postnatal maturation, using a modification of published techniques. In suckling (14-20 day) and post-weaning/mature (35-49 day) animals, membranes were purified approx. 10-fold, based upon the enrichment of ouabain-sensitive, sodium-potassium dependent adenosine triphosphatase activity. Membrane lipid analyses demonstrated age-dependent increases in total cholesterol and the cholesterol/phospholipid molar ratio, as well as decreases in phosphatidylethanolamine content and the fatty acid unsaturation index. Fluidity of basolateral membranes and membrane liposomes, determined from fluorescence anisotropy measurements using the lipid probes 1,6-diphenyl-1,3,5-hexatriene and DL-12-(9-anthroyl)stearic acid, demonstrated significant, ontogenic decreases in fluidity; and, additional studies showed that fluidity changes occurred early in the weaning period (by day 24 postnatally). Arrhenius plots of liposome anisotropies suggested a bilayer lipid thermotropic transition temperature of 22 degrees C in sucklings 26 degrees C in mature rabbits. These findings demonstrate that ontogeny of colonic basolateral membranes is associated with significant modulations in lipid composition and fluidity.     

Lipid composition and fluidity of liver plasma membranes from rats with chronic dietary iron overload

Liver plasma membranes isolated from rats with chronic dietary iron overload showed a large modification of their phospholipid fatty acid composition. Specifically, a significant decrease in polyunsaturated fatty acids and a parallel increase in saturated fatty acids was observed. This pattern was consistent with thein vivo occurrence of lipoperoxidative reactions in the liver plasma membranes. However, neither change in the cholesterol/phospholipid molar ratio nor in the lipid/protein ratio was detected. Direct measurement of the plasma membrane fluidity state by electron spin resonance spectrometry did not reveal any difference between control and iron-treated rats. These findings indicate that chronic dietary iron overload can induce lipid peroxidation of rat liver plasma membranes, but this event does not bring about modification in the physical state of the membrane.     

The response of multilamellar liposomes to freezing and thawing

The use of liposomes as a model system for investigating the mechanism of freezing injury was investigated. Modification of the liposome phospholipid and cholesterol content allows a correlation to be made between the composition of a membrane system and its response to the stresses of freezing and thawing. The data on phase transitions are contradictory in the sense that liposomes become more sensitive to freezing injury following treatments which both increase or decrease phase transition temperature. In contrast the effect of cholesterol in sensitizing membranes to the stresses of freezing and thawing appears to be more fundamental. Direct cryomicroscope observations of liposomes during slow cooling indicate that they are osmotically active at low temperatures and upon thawing morphological alterations to the membranes occur. The response of liposomes following cooling at a range of rates to ?196 °C and the effects of cryoprotective additives are similar to those observed with many cell types. These results indicate that liposomes are a valid model for investigating the biochemistry of membrane damage induced by the stresses of freezing and thawing.     

Membrane lipids and morphology of brain cortex synaptosomes isolated from hibernating Yakutian ground squirrel

Synaptosomes were isolated from Yakutian ground squirrel brain cortex of summer and winter hibernating animals in active and torpor states. Synaptosomal membrane cholesterol and phospholipids were determined. The seasonal changes of synaptosomal lipid composition were found. Synaptosomes isolated from hibernating Yakutian ground squirrel brain cortex maintained the cholesterol sphingomyelin, phosphatidylethanolamine, lysophosphatidylcholine, cardiolipin, phosphatidylinositol and phosphatidylserine contents 2.5, 1.8, 2.6, 1.8, 1.6, and 1.3 times less, respectively, and the content of phosphatidylcholine twice as much as the one in summer season. The synaptosomal membrane lipid composition of summer animals was shown to be markedly different from that as hibernating ground squirrels and non-hibernating rodents. It is believed that phenotypic changes of synaptosomal membrane lipid composition in summer Yakutian ground squirrel are the important preparation step for hibernation. The phosphatidylethanolamine content was increased in torpor state compared with winter-active state and the molar ratio of cholesterol/phospholipids in synaptosomal membrane of winter torpor ground squirrels was lower than that in active winter and summer animals. These events were supposed to lead to increase of the synaptosomal membrane fluidity during torpor. Synaptosomes isolated from torpor animals have larger sizes and contain a greater number of synaptic vesicles on the synaptosomal profile area. The synaptosomal membrane lipid composition and synaptosome morphology were involved in phenotypic adaptation of Yakutian ground squirrel to hibernation.     

Fluidity of natural membranes and phosphatidylserine and ganglioside dispersions. Effect of local anesthetics, cholesterol and protein.

The microviscosity of artificial lipid membranes and natural membranes was measured by the fluorescence polarization technique employing perylene as the probe. Lipid dispersions composed of brain gangliosides exhibited greater microviscosity than phosphatidylserine (268 cP vs 173 cP, at 25 degrees C). Incorporation of cholesterol (30-50%) increased the microviscosity of lipid phases by 200-500 cP. Cholesterol's effect on membrane fluidity was completely reversed by digitonin but not by amphotericin B. Incorporation of membrane proteins into lipid vesicles gave varying results. Cytochrome b5 did not alter membrane fluidity. However, myelin proteolipid produced an apparent increase in microviscosity, but this effect might be due to partitioning of perylene between lipid and protein binding sites since tha latter have a higher fluorescence anisotropy than the lipid. The local anesthetics tetracain and butacaine increased the fluidity of lipid dispersions, natural membranes and intact ascites tumor cell membranes. The effect of anesthetics appears to be due to an increased disordering of lipid structure. The fluidity of natural membranes at 25 degrees C varied as follows: polymorphonuclear leukocytes, 335 cP; bovine brain myelin, 270 cP; human erythrocyte, 180 cP; rat liver microsomes, 95 cP; rat liver mitochondria, 90 cP. In most cases the microviscosity of natural membranes reflects their cholesterol: phospholipid ratio. The natural variations in fluidity of cellular membranes probably reflect important functional requirements. Similarly, the effects of some drugs which alter membrane permeability may be the result of their effects on membrane fluidity.     

Differential temperature acclimatization responses in the membrane phospholipids of Posthodiplostomum minimum and its second intermediate host, Lepomis macrochirus

The effects of temperature change on phospholipid content in metacercariae of Posthodiplostomum minimum and their second intermediate hosts, Lepomis macrochirus, were examined to gauge similarities in the homeoviscous adaptation of host and parasite membranes to environmental thermal change. Heart, liver, and muscle tissues from individual L. macrochirus responded to environmental temperature declines with a decrease in the ratio of phosphatidylethanolamine (PE) to phosphatidylcholine (PC). Increases in membrane PE concentration increase membrane fluidity, maintaining fish membrane function as environmental temperature declines. However, the metacercariae of P. minimum exhibit changes in cholesterol levels, total lipid levels, and lipid composition (PE/PC) that contrast the normal changes for homeoviscous membrane adaptation exhibited by their fish intermediate hosts. The parasites seem to rely on their hosts for homeoviscous adaptation within normal developmental temperature ranges, pooling both cholesterol and PE as energetic stores for development and ontological transitions signaled by elevated temperatures.     

Lipid composition of the isolated rat intestinal microvillus membrane

1. Rat intestinal microvillus plasma membranes were prepared from previously isolated brush borders and the lipid composition was analysed. 2. The molar ratio of cholesterol to phospholipid was greatest in the membranes and closely resembled that reported for myelin. 3. Unesterified cholesterol was the major neutral lipid. However, 30% of the neutral lipid fraction was accounted for by glycerides and fatty acid. 4. Five phospholipid components were identified and measured, including phosphatidylethanolamine, phosphatidylcholine, phosphatidylserine, sphingomyelin and lysophosphatidylcholine. Though phosphatidylethanolamine was the chief phospholipid, no plasmalogen was detected. 5. In contrast with other plasma membranes in the rat, the polar lipids of the microvillus membrane were rich in glycolipid. The cholesterol:polar lipid (phospholipid+glycolipid) ratio was about 1:3 for the microvillus membrane. Published data suggest that this ratio resembles that of the liver plasma membrane more closely than myelin or the erythrocyte membrane. 6. The fatty acid composition of membrane lipids was altered markedly by a single feeding of safflower oil. Membrane polar lipids did not contain significantly more saturated fatty acids than cellular polar lipids. Differences in the proportion of some fatty acids in membrane and cellular glycerides were noted. These differences may reflect the presence of specific membrane glycerides.     

Lipid topology and physical properties of the outer mitochondrial membrane of the yeast, Saccharomyces cerevisiae

The outer membrane of yeast mitochondria was studied with respect to its lipid composition, phospholipid topology and membrane fluidity. This membrane is characterized by a high phospholipid to protein ratio (1.20). Like other yeast cellular membranes the outer mitochondrial membrane contains predominantly phosphatidylcholine (44% of total phospholipids), phosphatidylethanolamine (34%) and phosphatidylinositol (14%). Cardiolipin, the characteristic phospholipid of the inner mitochondrial membrane (13% of total phospholipids) is present in the outer membrane only to a moderate extent (5%). The ergosterol to phospholipid ratio is higher in the inner (7.0 wt%) as compared to the outer membrane (2.1 wt.%). Attempts to study phospholipid asymmetry by selective degradation of phospholipids of the outer leaflet of the outer mitochondrial membrane failed, because isolated right-side-out vesicles of this membrane became leaky upon treatment with phospholipases. Selective removal of phospholipids of the outer leaflet with the aid of phospholipid transfer proteins and chemical modification with trinitrobenzenesulfonic acid on the other hand, gave satisfactory results. Phosphatidylcholine and phosphatidylinositol are more or less evenly distributed between the two sides of the outer mitochondrial membrane, whereas the majority of phosphatidylethanolamine is oriented towards the intermembrane space. The fluidity of mitochondrial membranes was determined by measuring fluorescence anisotropy using diphenylhexatriene (DPH) as a probe. The lower anisotropy of DPH in the outer as compared to the inner membrane, which is an indication for an increased lipid mobility in the outer membrane, was attributed to the higher phospholipid to protein and the lower ergosterol to phospholipid ratio. The data presented here show, that the outer mitochondrial membrane, in spite of its close contact to the inner membrane, is distinct not only with respect to its protein pattern, but also with respect to its lipid composition and physical membrane properties.     

Correction of abnormal lipid fluidity and composition of rat ileal microvillus membranes in chronic streptozotocin-induced diabetes by insulin therapy

Diabetes was induced in rats by administration of streptozotocin. After 90-120 days, one group of chronic diabetic animals was treated with insulin for chronic diabetic animals was treated with insulin for 10 days. The lipid fluidity and composition of microvillus membranes prepared from ileal enterocytes of control, diabetic, and insulin-treated diabetic animals were determined. Lipid fluidity, as assessed by steady-state fluorescence polarization techniques using the probes 1,6-diphenyl-1,3,5-hexatriene, DL-2-(9-anthroyl)stearic acid and DL-12-(9-anthroyl)stearic acid, was decreased in membranes of diabetic animals compared to membranes of control and insulin-treated diabetic membranes. The differences in fluidity resulted from an increased cholesterol content and cholesterol/phospholipid molar ratio in membranes of diabetic animals. The activities of sucrase and alkaline phosphatase were also found to be higher in membranes of diabetic animals. Insulin treatment, however, failed to significantly influence the enzymatic activities of these membranes. These studies, therefore, demonstrate that alterations in the lipid fluidity, lipid composition, and certain enzymatic activities exist in microvillus membranes of enterocytes prepared from chronic streptozotocin-induced diabetic rats. Administration of insulin for 10 days to these animals restored membrane fluidity and lipid composition but not enzymatic activities to control membrane levels.     

Age-Related Differences in Synaptosomal Peroxidative Damage and Membrane Properties

Young, adult, and old rats were used to study the effect of age on the integrity and functioning of brain synaptosomes. An evaluation was made of the differences in lipid composition, membrane fluidity, Na+, K(+)-ATPase activity, and susceptibility to in vitro lipid peroxidation. There was an age-related increase in synaptosomal free fatty acids, with no modification in acyl chain composition, and a decrease in membrane phospholipids which increased the cholesterol/phospholipid mole ratio. With altered lipid composition, there was a corresponding age-dependent decrease in membrane fluidity, a reduction of Na+, K(+)-ATPase activity, and an overall greater susceptibility to in vitro lipid peroxidation. Furthermore, lipid peroxidation promoted strong modifications of the membrane fluidity, lipid composition, and Na+,K(+)-ATPase activity just as aging did, thus indicating a possible contribution of oxidative damage to ageing processes. The cases studied revealed that the greater responsiveness of old membranes to in vitro lipid peroxidation resulted in the highest degree of membrane alteration, indicating that all pathological states known to promote a peroxidative injury can have even more dramatic consequences when they take place in old brain.     

Changes in the lipid content of boar sperm plasma membranes during epididymal maturation

Plasma membranes of boar sperm from caput, corpus and cauda of the epididymis were purified by differential- and sucrose-density equilibrium centrifugation and were found to yield a single band at a density of 1.13 g/cm3. This fraction was enriched in acid and alkaline phosphatase, 5'-nucleotidase and (Na+ + K+)-ATPase activities, whereas it contained minimal amounts of hyaluronidase and N-acetylglucosaminidase and no succinic acid dehydrogenase activities. The plasma membrane of caput, corpus and cauda sperm had the same phospholipid/protein and cholesterol/phospholipid ratios but yielded different amounts of protein and individual lipid classes. Several changes in the plasma membrane were observed during transit of sperm through the epididymis. Within the phospholipid class a decrease in the percentage of phosphatidylethanolamine, phosphatidylserine and phosphatidylinositol was detected accompanied by an increase in amount of phosphatidylcholine, sphingomyelin and polyphosphoinositides. In the other lipid classes there was a decrease in the amount of free fatty acid and the major glycolipid. The amount of cholesterol decreased, while the amount of desmosterol and cholesterol sulfate increased. There was an increase in the amount of diacylglycerol. In addition, the changes in the fatty acid composition of the total membrane lipid and each phospholipid were determined. The above changes in the lipid composition of the plasma membrane during epididymal maturation may help to explain the decreased resistance to cold shock and changes in membrane fluidity of sperm during transit in the epididymis.     

Factors contributing to the distribution of cholesterol among phospholipid vesicles

The distribution of cholesterol between vesicles of different lipid composition at equilibrium has been determined. Small, sonicated unilamellar vesicles and large unilamellar vesicles were incubated at a defined temperature, and aliquots were then obtained at selected times for analysis. Inclusion of a small amount of phosphatidylserine or phosphatidylinositol in the membrane does not appreciably affect the distribution of cholesterol at equilibrium by these measurements. A membrane in the gel state is a poor acceptor of cholesterol. The length of the hydrocarbon chain on the phospholipid may also play a role. Bovine brain sphingomyelin dramatically slows the kinetics of cholesterol transfer, and the equilibrium distribution of cholesterol among vesicles containing sphingomyelin is therefore not observable in these experiments. Data obtained with vesicles containing phosphatidylethanolamine indicate a preference of cholesterol for vesicles composed of phosphatidylcholine compared to vesicles consisting primarily of phosphatidylethanolamine, at equilibrium. Experiments with a chaotropic agent indicate that the nature of the surface of the phosphatidylethanolamine bilayer, and its hydration, are important factors in the distribution of cholesterol among membranes in which phosphatidylethanolamine is present. These data suggest that membrane lipid content may play a role in the distribution of cholesterol among the membranes of a cell.     

Plasma membrane changes associated with rat liver regeneration

The lipid composition and fluidity of plasma membranes have been studied at different stages of liver regeneration (4, 15 and 24 h after surgery). The phospholipid and fatty acid composition is not modified, whereas the cholesterol/phospholipid ratio is lower with respect to control membranes. The modification of the physical properties of the membranes has been studied directly by EPR analysis and indirectly by temperature dependence and cooperativity of some membrane-bound enzymes (Mg2+-ATPase, (Na+ + K+)-ATPase and 5'nucleotidase). Surgical operation or anaesthesia alone causes an early increase in fluidity; such an effect appears to be markedly reduced at a later stage. There seems to be a marked effect of regeneration on plasma membrane fluidity 15 h after partial hepatectomy when several parameters--surface fluidity, cholesterol/phospholipid ratio, and 5'-nucleotidase activity in the presence of concanavalin A -- are modified and indicate an increase in membrane fluidity. It is suggested that this modification of membrane properties could be related to the proliferative process.     

Effect of freezing and cold storage on phospholipids in developing soybean cotyledons

Freezing of plant tissue adversely affects lipid composition. Immature soybean cotyledons (Glycine max L. Merr.) var. “Harosoy 63” were frozen with liquid N₂, dry ice, or stored in a freezer (−20 C) before lipid extraction. The effects of freezing temperature, thawing rate, and cold storage on the lipid composition of frozen tissue revealed significantly higher levels of phosphatidic acid, and diminished levels of phosphatidylcholine, phosphatidylethanolamine, and N-acylphosphatidylethanolamine from the control. Regardless of freezing temperature, phosphatidic acid levels increased from 4.7 mole% to nearly 50 mole% of the total phospholipid when frozen tissues were stored 10 days at −20 C. During the same period, N-acylphosphatidylethanolamine decreased from 54.1 mole% to 6.6 mole% phospholipid. At least 8 mole% of the phosphatidic acid increase occurred during slow thawing of the frozen tissues. In autoclaved samples, phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine, and N-acylphosphatidylethanolamine levels were not different from the control. Labeling of the lipid-glycerol with ³H, and fatty acids with ¹⁴C, demonstrated the degradation product was primarily phosphatidic acid. Apparently enzymic destruction of the phospholipids occurred during freezing, cold storage, and thawing.     

Physical properties, lipid composition and enzyme activities of hepatic subcellular membranes from chick embryo after ethanol treatment.

Exposure of chick embryos to ethanol resulted in significant alterations to the lipid composition of various different hepatic subcellular membranes. A marked decrease in cholesterol levels and an increase in the phospholipid content of microsomes and mitochondria was observed. Ethanol also affected the fatty acid profiles, mainly by decreasing the percentage of oleic acid in phosphatidylcholine and phosphatidylethanolamine in the mitochondria and phosphatidylethanolamine in the microsomes. In spite of these changes ethanol only induced alterations in the fluidity of the mitochondrial membranes, which showed a more rigid core, in contrast to the phospholipid-head region, which was not affected. In accordance with the changes observed in the physical state of the membrane, the enzymes involved in the microsomal electron-transport systems were not modified by ethanol, while cytochrome oxidase activity decreased by 50% compared to the activity in the mitochondria from control chick embryos. These findings establish that during the chick-embryo developmental period the mitochondria are more sensitive to ethanol than are the microsomes.