Phospholipids and biomembranes

The fatty acid and aldehyde composition of the major phospholipids of mouse brain

Phospholipid classes were separated from mouse brain lipid extracts by preparative thin-layer chromatography (TLC). Methyl esters were prepared from the intact phospholipids by direct transesterification at room temperature in the presence of silica gel by using 0.5M: NaOH-methanol in order to prevent interference by aldehydes or derivatives. Dimethyl acetal derivatives of phosphoglyceride alkenyl ethers (alkenyl moiety with a double bond in 1,2-position relative to oxygen linkage) were prepared, using 5% concentrated HCl in methanol, followed by preparative TLC for isolation.The major phospholipids present were ethanolamine phosphoglycerides (EPG) 39.8%, choline phosphoglycerides (CPG) 39.7%, serine phosphoglycerides (SPG) 15.0%, and sphingomyelin (Sph) 5.4%. One-fifth of the total phospholipids (PL) were in the form of plasmalogens, mainly EPG. Choline and serine plasmalogens were present in trace quantities. The major aldehyde components of the plasmalogens were 16ratio0, 18ratio0, and 18ratio1.The EPG were rich in long-chain poly-unsaturated fatty acids, including 28.8% of 22ratio6 and 17.0% of 20ratio4, but contained only 7.2% of 16ratio0. In contrast, the CPG contained 39.6% of 16ratio0, and 31.0% of 18ratio1 with a small content of polyunsaturated fatty acids. The SPG exhibited a still different pattern containing 38.2% of 18ratio0, 23.2% of 18ratio1, 24.3% of 22ratio6, 2.9% of 16ratio0, and 3.8% of 20ratio4.

Mitochondrial glycerol-3-phosphate acyltransferase-deficient mice have reduced weight and liver triacylglycerol content and altered glycerolipid fatty acid composition

Microsomal and mitochondrial isoforms of glycerol-3-phosphate acyltransferase (GPAT; E.C. 2.3.1.15) catalyze the committed step in glycerolipid synthesis. The mitochondrial isoform, mtGPAT, was believed to control the positioning of saturated fatty acids at the sn-1 position of phospholipids, and nutritional, hormonal, and overexpression studies suggested that mtGPAT activity is important for the synthesis of triacylglycerol. To determine whether these purported functions were true, we constructed mice deficient in mtGPAT. mtGPAT(-/-) mice weighed less than controls and had reduced gonadal fat pad weights and lower hepatic triacylglycerol content, plasma triacylglycerol, and very low density lipoprotein triacylglycerol secretion. As predicted, in mtGPAT(-/-) liver, the palmitate content was lower in triacylglycerol, phosphatidylcholine, and phosphatidylethanolamine. Positional analysis revealed that mtGPAT(-/-) liver phosphatidylethanolamine and phosphatidylcholine had about 21% less palmitate in the sn-1 position and 36 and 40%, respectively, more arachidonate in the sn-2 position. These data confirm the important role of mtGPAT in the synthesis of triacylglycerol, in the fatty acid content of triacylglycerol and cholesterol esters, and in the positioning of specific fatty acids, particularly palmitate and arachidonate, in phospholipids. The increase in arachidonate may be functionally significant in terms of eicosanoid production.

Application of pressure perturbation calorimetry to lipid bilayers

Pressure perturbation calorimetry (PPC) is a new method that measures the heat consumed or released by a sample after a sudden pressure jump. The heat change can be used to derive the thermal volume expansion coefficient, alpha(V), as a function of temperature and, in the case of phase transitions, the volume change, DeltaV, occurring at the phase transition. Here we present the first report on the application of PPC to determine these quantities for lipid bilayers. We measure the volume changes of the pretransition and main transition of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and the thermal expansivity of the fluid phase of DMPC and of two unsaturated lipids, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and 1,2-dioleoyl-sn-glycero-3-phosphocholine. The high sensitivity of PPC instrumentation gives accurate data for alpha(V) and DeltaV even upon the application of relatively low pressures of approximately 5 bar.

Effect of growth temperature on the positional distribution of eicosapentaenoic acid and trans hexadecenoic acid in the phospholipids of a Vibrio species of bacterium

Phosphatidylethanolamine (PE) and phosphatidylglycerol (PG) were isolated from a Vibrio species of bacterium, known to produce eicosapentaenoic acid (20:5n-3) and trans-hexadecenoic acid (16:1n-7), and subjected to phospholipase A2 degradation to determine the positional distribution of component fatty acids. At the two growth temperatures studied (20 and 5 degrees C), both 20:5n-3 and trans 16:1 n-7 were located mainly at position sn-2 in PE. Increases in the proportions of 20:5n-3 and trans 16:1n-7 in position sn-2 with decreasing growth temperature were balanced mainly by decreases in the level of iso-15:0. In PG, trans 16:1n-7 was located predominantly in position sn-1, although the difference between the two positions was not as great as in PE. Eicosapentaenoic acid was preferentially located in position sn-2 of PG, particularly at 5 degrees C when it comprised 29.9% of the total fatty acids in this position. It is concluded that trans 16:1n-7/20:5n-3 is not a major molecular species of phospholipid in this species of Vibrio and that changes in the levels of molecular species of PE containing iso-15:0 may feature in thermal acclimation.

Characterization of three choline transport activities in Rhizobium meliloti: modulation by choline and osmotic stress

Choline has both a nutritional and osmoregulatory role in Rhizobium meliloti (T. Bernard, J. A. Pocard, B. Perroud, and D. Le Rudulier, Arch. Microbiol. 143:359-364, 1986). In view of this fact, choline transport was studied in R. meliloti 102F34 to determine how the rate of choline uptake is modulated. The effects of the cultural conditions on the kinetics of transport are presented. A high-affinity activity and a low-affinity activity were found in cells grown in minimal medium. The addition of 0.3 M NaCl or other osmolytes to the medium resulted in a marked decrease in the high-affinity activity, whereas the low-affinity activity remained fairly constant. Furthermore, results from osmotic upshock and downshock experiments indicate that the response of the cell to high osmolarity is rapid; hence, the mechanism of regulation by salt likely does not involve gene induction. A second high-affinity transport activity was induced by choline itself. Like the constitutive low-affinity transport activity, this activity was not greatly altered when the cells were grown in media of elevated osmotic strength. We conclude that although all three kinetically distinct transport systems are efficient at low osmolarity, only the induced high- and low-affinity activities are important for osmoregulation. The characteristics of the three transport activities from R. meliloti are compared with those from other bacterial species that use choline for growth and/or osmoregulation.

Lipid shape as a determinant of lipid composition in Clostridium butyricum. The effects of incorporation of various fatty acids on the ratios of the major ether lipids

The lipid composition of Clostridium butyricum is strongly influenced by the aliphatic chain compositions of the membrane lipids. Growth on cis-monounsaturated fatty acids in the absence of biotin was shown to affect the relative proportions of phosphatidylethanolamine, plasmenylethanolamine, and the glycerol acetal of plasmenylethanolamine most strongly, with smaller effects on the acidic lipids, phosphatidylglycerol and cardiolipin. The ratio of the glycerol acetal of plasmenylethanolamine to total phosphatidylethanolamine in cells grown on a series of fatty acids is shown to decrease in the following order; cis-vaccenic acid greater than or equal to oleic acid = C19-cyclopropane fatty acid greater than linoleic acid greater than petroselinic acid greater than elaidic acid greater than 14-methylhexadecanoic acid (anteiso-C17) greater than 12-methyltridecanoic acid (iso-C14). All fatty acids were extensively incorporated into the lipid acyl, alkenyl, and alkyl chains. There was considerable chain-elongation of the iso-C14 to iso-C16. The results are consistent with the hypothesis that the membrane lipid composition is strongly influenced by lipid shape and that the observed changes in lipid composition serve to stabilize the bilayer arrangement of the cell membrane.

Inhibition of the antidiuretic hormone hydroosmotic response by phospholipids and phospholipid metabolites

Phospholipid metabolities and phospholipids containing arachidonic acid (AA) inhibited the antidiuretic hormone (ADH)-induced increase in transepithelial water flow in the toad urinary bladder, but had no effect on basal water flow when added to the serosal bathing solution. Other fatty acid-substituted phospholipid metabolites had no effect on osmotic water movement in the presence or absence of ADH. Indomethacin attenuated the inhibitory effects of the AA containing phospholipid metabolities (PMAA), suggesting that the PMAA response required AA release and prostaglandin (PG) formation. PMAA increased PGE formation as measured by radioimmunoassay. PG have been reported to inhibit ADH-stimulated water flow by inhibiting adenylcyclase. PGE2 (10(-8) M) had no effect on cyclic AMP-stimulated water flow, whereas exogenous AA and PMAA attenuated the hydroosmotic response to added cyclic AMP. Indomethacin only partially reversed the inhibition by AA of the cyclic AMP-associated water movement, suggesting that the inhibition by AA and PMAA may involve other metabolites of AA than PG. PG and the AA cascade have been implicated as cellular modulators of the ADH hydroosmotic response. The present results offer additional support to the theory that this system may regulate the intracellular events that are transduced following receptor activation by ADH.

Modification of microsomal lipid composition and electron transport enzyme activities in isovalerate-supplemented cells of novel Tetrahymena ISO

Tetrahymena ISO cells, which have an unusually high level of iso odd-numbered fatty acids, were grown medium supplemented with various concentrations of isovalerate. There was a marked increase in the total proportion of iso odd-numbered fatty acids in supplemented whole cells (28.9 leads to 70.3%) and microsomes (37.7 leads to 84%), with a corresponding decrease in normal fatty acids, although no significant alteration of phospholipid composition was observed during 11 hr isovalerate-supplementation. Microsomal palmitoyl-CoA and stearoyl-CoA desaturase activities in isovalerate-supplemented cells decreased by 45.7% and 30.6% during 11 hr, respectively. NADH-cytochrome c reductase and NADH-ferricyanide reductase activities as well as the content of cytochrome b560ms, which is similar to mammalian microsomal cytochrome b5, were reduced in microsomes from 11 hr-supplemented cells, whereas NADPH-cytochrome c reductase activity was constant. It is suggested that the alteration of the cross-sectional area of lipid molecules in the bilayer, which results from the replacement of normal fatty acids with iso- 15:0 and iso- 17:1, would result in the decline of palmitoyl- and stearoyl-CoA desaturation in the isovalerate-supplemented cells, in order to maintain membrane fluidity at a functional level.

Distribution of long chain polyenoic acids among phospholipids of mouse testis

Fatty acid composition of phospholipid (PL) classes was measured in mouse testis. Among the long-chain polyenoic acids (LCPA), 22:6 was found in highest concentration in phosphatidylethanolamine (PE), whereas percentages of 20:4 and 22:5 were not different in PE than in phosphatidycholine. Each PL class had a unique fatty acid composition which was also different from that of triglycerides and cholesteryl esters. Differential metabolisms of 22:5 and 22:6 suggest different roles for these fatty acids in mouse testis. Tissue-specific functions of LCPA in mouse spermatogenesis may be divided between 22:5 and 22:6.

Acyl-CoA synthetase activity of rat liver microsomes. Substrate specificity with special reference to very-long-chain and isomeric fatty acids

1. A fatty acid-depleted rat liver microsomal fraction has been used for the measurement of acyl-CoA synthetase (acid : CoA ligase (AMP-forming), EC 6.2.1.3) activity. The assay was based on measurement of the reaction product AMP by high-performance liquid chromatography (HPLC). The synthetase activity (V') revealed an optimum at 12 : 0 with saturated fatty acids as substrate, and at 14 : 1 with mono-unsaturated fatty acids. The apparent Michaelis constant, on the other hand, showed no systematic dependence on the fatty acid chain-length. 2. The mono-unsaturated fatty acids from 14 : 1 to 22 : 1 gave higher activities than the corresponding saturated fatty acids, and the relative differences were greatest with the very-long-chain fatty acids eicosaenoic (20 : 1 (11) (cis)) and docosaenoic acid (22 : 1 (11) (cis)). The synthetase activity with saturated and mono-unsaturated fatty acids was found to correlate to their capacity factor (k') on reversed phase chromatography (HPLC). This finding may indicate that the observed chain-length dependence of the activity largely reflects the partition of the fatty acids between a hydrophobic and a hydrophilic phase. In general, the position of the double bond and the cis/trans configuration had little effect on the V' values except for 22 : 1 (11)(cis) which revealed a 2-fold higher activity tha 22 : 1 (13) (cis). 3. The polyunsaturated fatty acid 22 : 6 (all cis) ;was notably found to be a much better substrate than other C22 fatty acids. 4. The present study does not support the idea of more than a single ATP-dependent acyl-CoA synthetase in the rat liver microsomal fraction.

Fluorescence quenching in model membranes. 3. Relationship between calcium adenosinetriphosphatase enzyme activity and the affinity of the protein for phosphatidylcholines with different acyl chain characteristics

The dependence of function and lipid binding affinity of an integral transport protein on the fatty acyl chain characteristics of a membrane-forming phospholipid have been determined. When a newly developed fluorescence quenching technique [London, E., & Feigenson, G. W. (1981) Biochemistry (first paper of three in this issue); London, E., & Feigenson, G. W. (1981) Biochemistry (preceding paper in this issue)] is used for examining lipid-protein interactions in membranes, the Ca2+ ATPase from rabbit sarcoplasmic reticulum is found to bind with equal affinity a large variety of phosphatidylcholines used to reconstitute the protein into enzymatically active vesicles, regardless of fatty acyl chain length or details of unsaturation. In parallel with the lipid binding studies, we have measured the sensitivity of the catalytic activity of the Ca2+ ATPase to the fatty acyl chain characteristics of the phosphatidylcholine membranes in which the enzyme was reconstituted. The enzyme appears to be sensitive only to the effective fatty acyl chain length, which determines the thickness of the bilayer in which the protein is inserted and displays little sensitivity to such details of unsaturation as degree, position, and isomeric type. Both ATP hydrolyzing and Ca2+ transporting activities of the enzyme were similarly affected by bilayer thickness, and maximum activity was observed in membranes of intermediate thickness. These observations are reconciled in a number of possible models for the manner in which this integral protein interacts with membranes of varying thickness. A freeze-thaw method was used to reconstitute the Ca2+ ATPase, and the vesicles so obtained have been characterized by gel permeation chromatography, density gradient centrifugation, and electron microscopy, (thin section). Convenient methods are described for (a) rapidly separating reconstituted Ca2+ ATPase from unincorporated protein simultaneously in a large number of small samples, giving good recovery of fractionated vesicles without significant dilution, and (b) measuring leakiness to Ca2+ of reconstituted vesicles. Additionally, the gel and liquid-crystal phase transition temperature and bilayer thickness have been determined respectively by differential thermal analysis and low-angle X-ray diffraction for some of the synthetic phosphatidylcholines, which range in chain length from 12 to 24 carbon atoms.

Properties and biosynthesis of cyclopropane fatty acids in Escherichia coli

The lipid phase transition of Escherichia coli phospholipids containing cyclopropane fatty acids was compared with the otherwise homologous phospholipids lacking cyclopropane fatty acids. The phase transitions (determined by scanning calorimetry) of the two preparations were essentially identical. Infection of E. coli with phage T3 inhibited cyclopropane fatty acid formation over 98%, whereas infection with mutants which lack the phage coded S-adenosylmethionine cleavage enzyme had no effect on cyclopropane fatty acid synthesis. These data indicate that S-adenosylmethionine is the methylene in cyclopropane fatty acid synthesis.

The structure of oriented sphingomyelin bilayers

X-ray diffraction from oriented bilayers of sphingomyelin gave up to 14 orders of diffraction of a lamellar repeat of 68.5 A on the merididan and up to eight reflections, including a strong reflection at 4.2 A, on the equator. The diffraction spacings did not change when the sphingomyelin bilayers were exposed to different humidities. A direct analysis of the low resolution X-ray data, using deconvolution is presented. A comparison of the Patterson functions of sphingomyelin with those of phosphatidylcholine and phosphatidylethanolamine suggests that the molecular structure of sphingomyelin in oriented bilayers resembles the structure of both phosphatidylcholine and phosphatidylethanolamine. Molecular model calculations for sphingomyelin bilayers have also been performed. Electron density profiles of sphingomyelin bilayers at resolution of about 6 A and about 2.5 A are presented. Our results indicate that the phosphorylcholine head group of sphingomyelin is in the plane of the membrane and at right angles to the hydrocarbon chains, the hydrocarbon chains are nearly parallel to each other, and there is only a limited, if any, interdigitation of the hydrocarbon chains of the adjacent sphingomyelin molecules in the bilayer.

Membrane lipid biosynthesis in Acholeplasma laidlawii B: incorporation of exogenous fatty acids into membrane glyco- and phospholipids by growing cells

The extent of incorporation of a wide variety of exogenous saturated, unsaturated, branched-chain, and cyclopropane fatty acids into the membrane lipids of Acholeplasma laidlawii B was systematically studied. Within each fatty acid class the extent of incorporation generally increased markedly with increasing chain length, reached a maximum, and then declined progressively but less sharply with further increases above that chain length giving maximal direct incorporation. Certain shorter-chain members of each fatty acid class underwent complete or partial conversion to longer-chain homologues before utilization for complex lipid biosynthesis. The degree and extent of chain elongation and direct incorporation and the characteristic dependence of each of these processes on fatty acid chain length and structure correlated well with the physical properties (melting temperatures) of the exogenous fatty acids. The in vivo specificity of the enzyme systems responsible for the incorporation of exogenous fatty acids was such that the fluidity and physical state of the membrane lipids were maintained within a definite, albeit a relatively wide, range. We also observed that the neutral glycolipids typically have similar fatty acid compositions, which are somewhat different from those of the major phosphatides, which also exhibit similar fatty acid spectra. The phosphorylated glycolipid glycerophosphoryldiglucosyl diglyceride, however, always maintained a unique fatty acid composition quite different from that of the diglucosyl diglyceride from which it is presumably derived. These characteristic differences in fatty acid composition appear to function to minimize differences in phase transition temperatures, thus producing a more physicochemically homogeneous mixture of membrane lipids than would result from a nonspecific incorporation of fatty acids.

Modification of fatty acid composition of rat heart lipids by feeding cod liver oil

Modification of the fatty acid composition of cardiac phospholipids and neutral lipids was studied in rats fed a diet containing 10% cod liver oil. The results reflect the dynamic state of esterified fatty acids in neutral lipids and phospholipids of heart muscle. In cardiac neutral lipids there was a moderate but significant increase in exogenous fatty acids, 20:1(n--9), 22:1(n--11), 20:5(n--3) and 22:6(n--3), in animals fed cod liver oil, and a relative decrease in endogenous fatty acids, 16:0, 18:2(n--6 and 20:4(n--6). Increased dietary availability of 22: 6(n--3) resulted in a major increase in the content of this fatty acid in phospholipids and replacement of 18:2(n--6) and 20:4(n--6). The 22:6(n--3) was able to replace one third of 18:2(n--6): further increase in 22: 6n--3) was accompanied by a decrease in 18:0. An inverse relationship between (n--6) and (n--3) polyene fatty acids in cardiac phospholipids suggests a replacement of (n--6) acids by (n--3) fatty acids.

Diet-induced changes in the fatty acid composition of mouse hepatocyte plasma membranes

Hepatocyte plasma membranes were isolated from the livers of mice fed either a low fat diet or high fat diets containing polyunsaturated or saturated fat. The combined rate and isopycnic ultracentrifugation technique which was used produced highly purified hepatocyte plasma membrane fractions. The efficacy of the procedure was checked by electron microscopy and the assay to marker enzymes for the different subcellular organelles. Mice were maintained on a low fat diet until 60-70 days of age, when they were fed high fat diets containing polyunsaturated fat. The hepatocyte plasma membrane lipids of mice fed the polyunsaturated fat diet for 4 wk contained increased proportions of the major dietary unsaturated fatty acid, linoleic acid, and increased proportions of arachidonic acid. The proportion of linoleic and arachidonic acids decreased with continued feeding of the polyunsaturated fat diet. The hepatocyte plasma membrane lipids of mice fed the saturated fat diet contained increased proportions of oleic acid.

Intramolecular disorder and its relation to mesophase structure in lipid/water mixtures

NMR spin-half pair dipolar echo measurements are reported for the lamellar (dispersions and multibilayer stacks) and hexagonal phases of potassium palmitate/2H2O mixtures. In the lamellar Lbeta and Lgamma (gel) phases the alkyl chains are rigid and perfectly ordered, while in the lamellar Lalpha and hexagonal phases they are flexible and disordered. In particular, the measurements show that in the fluid lamellar Lalpha phase the chain is "bent" at the C9-C10 segment; but is "straight" in the hexagonal phase.

The effects of isovalerate supplementation on growth and fatty acid composition of Tetrahymena pyriformis W

Cultures of Tetrahymena pyriformis W respond to isovalerate supplementation by an increase in odd-numbered saturated, unsaturated and alpha-hydroxy iso-fatty acids and by a decrease in even-numbered normal fatty acids in the glycerolipids and sphingolipids. Supplementation, however, did not alter the relative amount of unsaturated fatty acids found in the polar lipids. The unsaturated acids 17 : 1(i) and 19 : 1(i) were isolated from cells grown with [1-14C]isovalerate and found to have a higher specific activity than the monoenes of the normal series. Isotopic and gas-chromatographic analyses also indicated the presence of dienoic and trienoic acids of the iso-acid series. The iso-fatty acid content was elevated with isovalerate levels up to 5.0 mM and an inhibition of growth was noted. At higher concentrations of the short chain precursor, no further increase in total cellular iso-acids was detected although growth inhibition was more pronounced. The alpha-hydroxy iso-fatty acids of the sphingolipids, however, were elevated in a fashion that paralleled the external concentration of isovalerate; thus, the amount of alpha-hydroxy iso-acids and the degree of growth inhibition show a direct relationship. The increase in alpha-hydroxy iso-acid content of the sphingolipids was at the expense of the saturated normal and iso-acid components. The impact on the physiology of the cells can be envisaged as the result of changes in membrane fluidity due to the presence of high levels of iso-fatty acids without an accompanying reduction in unsaturated acids.

Freezing and melting of lipid bilayers and the mode of action of nonactin, valinomycin, and gramicidin

An abrupt loss of effectiveness of the presumed carriers, nonactin and valinomycin, in mediating ion conductance occurred at the same temperature as the membrane fluidity, judged visually, was lost. By contrast, the effects of the presumed channel-former, gramicidin, were the same on solid and liquid membranes. Taken together, these findings imply that freezing the membrane primarily reduces the mobility of these antibiotics with little effect on their solubility.

Fatty Acid Requirements of the Kazan 5 and Reiter Strains of Treponema pallidum

The fatty acid requirements of two avirulent treponemes were investigated by using a “lipid-poor” albumin-thioglycolate medium. The Kazan 5 and the Reiter stains of Treponema pallidum required a pair of fatty acids for growth. One member of the pair was saturated and the other was unsaturated. The saturated fatty acids could contain either an odd or even number of carbon atoms, but a chain length of at least 14 carbon atoms was necessary. Unsaturated fatty acids with one, two, or three double bonds were satisfactory if they contained 15 or more carbon atoms. The pair of fatty acids could be replaced with a single 18-carbon monounsaturated fatty acid if it was in the trans configuration rather than the naturally occurring cis form.

Metabolic turnover of the polar lipids of Mycoplasma laidlawii strain B

The fatty acyl groups of the membrane polar lipids of Mycoplasma laidlawii B were radioactively labeled by growth in the presence of (14)C-palmitic, oleic, or linoleic acids. No loss of radioactivity from any of the polar lipids occurred during incubation of radiolabeled cells in growth medium containing various nonradioactive fatty acids, although growth and lipid biosynthesis continued throughout the incubation period. The metabolism of the glucose and phosphate moieties was also studied in a similar fashion by utilizing growth in (14)C-glucose or (32)P-inorganic phosphate to radioactively label these groups. As before, no loss of radioactivity from any of the polar lipids occurred during subsequent growth in medium containing unlabeled glucose or phosphate. The results establish that the glyco- and phospholipids of M. laidlawii B are metabolically stable in actively growing cells. The absence of metabolic turnover is discussed in terms of proposed relationships between lipid metabolism and function in this organism.

Surface area of human erythrocyte lipids: reinvestigation of experiments on plasma membrane

Ratios of the lipid monolayer area to the erythrocyte surface area are 2:1 at low surface pressures and approach 1: 1 at collapse pressures. Un saturated phospholipids in cholesterol-phospholipid complexes of membrane ex tracts resemble their saturated derivatives at collapse pressures. Area ratio and phospholipid area data are related by an equation that tests hypothetical values for molecular areas used in membrane models.