Fatty Acyl Chain Composition Research Articles

Differences in membrane unsaturated fatty acids and electron spin resonance in different types of myeloid leukemia cells

The fatty acid composition and some physical properties of intact cells and isolated plasma membranes of two types of mouse myeloid leukemia cell clone grown in culture have been examined. One clone type, MGI +D +, can be induced by the macrophage and granulocyte-inducing protein (MGI) to differentiate into mature macrophages and granulocytes. The other clone type, MGI +D −, could not be induced to differentiate into mature cells. A two-fold increase in the ratio of saturated fatty acid to unsaturated fatty acid was found in the MGI +D − compared to the MGI +D + clones. The MGI +D − clones produced an unusual polyunsaturated C 20:5 fatty acid at 28°C, whereas the MGI +D + clones did not grow at this temperature. The cells and their isolated plasma membranes were studied by electron spin resonance. The motion of the 5-nitroxide stearate spin label was found to be higher in the intact cells and in the membranes of MGI +D − clones than of the MGI +D + clones. The cells of MGI +D + clones showed a similar freedom of motion to normal myeloblasts from the bone marrow. The results indicate that myeloid leukemia cells which differ in their competence to be induced to differentiate into mature cells have different physical properties of their plasma membranes and that this is correlated with their fatty acid acyl chain composition.

Asymmetric distribution of phosphatidylethanolamine fatty acyl chains in the membrane of vesicular stomatitis virus

The membrane of vesicular stomatitis virus (VSV) contains two distinct pools of phosphatidylethanolamine molecules which reside in the inner and outer phospholipid monolayers, respectively. 36% of the total membrane phosphatidylethanolamine is found in the outer monolayer while 64% is found in the inner. The two pools of VSV phosphatidylethanolamine can be distinguished operationally by the fact that only outer phosphatidylethanolamine is reactive in intact virions with the membrane-impermeable reagent trinitrobenzenesulfonate (TNBS). We have made use of this property to separate inner from outer VSV phosphatidylethanolamine and to determine the fatty acyl chain compositions of the two phosphatidylethanolamine pools separately. The results show that compared to outer phosphatidylethanolamine, inner phosphatidylethanolamine molecules contain a significantly higher proportion of unsaturated fatty acyl chains. Furthermore, whereas the proportion of unsaturated fatty acyl chains was found to be quite similar at the 1 and 2 glycerol carbon atoms in inner phosphatidylethanolamine, a marked dissimilarity was observed in outer phosphatidylethanolamine; outer phosphatidylethanolamine was enriched in saturated fatty acyl chains at the 1 position and in unsaturated fatty acyl chains at the 2 position. The differential fatty acyl chain composition of inner compared to outer phosphatidylethanolamine indicates that rapid, random transmembrane migration (flip-flop) of phosphatidylethanolamine does not occur in the VSV membrane. The nature of the fatty acyl chain asymmetry observed in VSV phosphatidylethanolamine does not support the view that the

Studies on Tetrahymena membranes in vivo manipulation of membrane lipids by [formula omitted] glycerol-feeding in Tetrahymena pyriformis

1. 1. Tetrahymena pyriformis NT-I cells were grown in the medium supplemented with 1-O- hexadecyl glycerol which is the precursor for alkyl ether-containing phospholipids; choline phosphoglyceride and 2-aminoethylphosphonolipid, and alterations in the plasma membrane and microsome lipid composition were examined. No incorporation of supplemented 1-O- hexadecyl glycerol was seen in ethanolamine phosphoglyceride. 2. 2. The hexadecyl glycerol fed membranes contain more polyunsaturated fatty acids than do the native membranes. However, the level of oleic acid (C 18 : 1) drops strikingly in the phospholipids of plasma and microsome membranes. 3. 3. The hexadecyl glycerol-feeding induced a remarkable alteration in the polar headgroup composition of plasma membrane, especially a large increase in 2-amino-ethylphosphonolipid with a compensatory decrease in ethanolamine phosphoglyceride of plasma membranes. 4. 4. The fatty acyl chain composition of phospholipids, especially ethanolamine phosphoglyceride, of the hexadecyl glycerol-fed plasma membranes and microsomes was found to be significantly different from that of the native membranes. 5. 5. These results may indicate that marked alterations in polar headgroup as well as fatty acyl chain composition of membranes induced by glyceryl ether-feeding would be required for maintaining proper membrane fluidity.

Studies on Tetrahymena membranes : Modification of surface membrane lipids by replacement of tetrahymanol by exogenous ergosterol in Tetrahymena pyriformis

Tetrahymena pyriformis WH-14 cells were grown in the medium supplemented with ergosterol (1 mg/100 ml) and the effects of replacement of tetrahymanol by ergosterol upon the lipid composition in the surface membranes (cilia and pellicles) were examined. 1. 1.|By scanning and freeze-etch electron microscopy it was suggested that exogenous ergosterol would be inserted into the lipid regions in the surface membranes. Although freeze-etched faces of filipin-treated membranes containing the native tetrahymanol showed a random distribution of 85-Å protein particles, the ergosterol-replaced membranes after the same polyene treatment revealed the marked ultrastructural alterations on the fracture faces. 2. 2.|The replacement of tetrahymanol in membranes by ergosterol induced a profound alteration in the phospholipid class composition and a marked increase in phosphatidylethanolamine with a compensatory decrease in phosphatidylcholine and 2-aminoethylphosphonolipid. 3. 3.|There are significant and quantitative but not qualitative changes in the fatty acid composition of total lipids from the ergosterol-replaced membranes. There are also increases in saturated and decreases in unsaturated fatty acids. Phosphatidylethanolamine acyl chains particularly become more saturated, as compared with two other phospholipids, in ergosterol-replaced pellicles. This increase in saturation is due to an appreciable increase in C 14 : 0, C 16 : 0 and iso-C 17 : 0, and a decrease in C 18 : 1( Δ 9 ), C 18 : 2(Δ 9, 12) and C 18 : 3(Δ 6, 9, 12 ). 4. 4.|These results suggest that profound alterations in phospholipids as well as in their fatty acyl chains are required to modify the overall membrane lipid composition for the maintenance of proper membrane fluidity. Our data would also support the thesis that polar head groups are involved in the membrane lipid organization and that sterols interact selectively with phospholipid molecules containing the appropriate fatty acyl chain composition in biological membranes.

Effects of Phospholipid Acyl Chain Fluidity, Phase Transitions, and Cholesterol on (Na+ + K+)-stimulated Adenosine Triphosphatase

A soluble delipidized (Na + K)-stimulated ATPase was obtained from rabbit kidney outer medulla by the use of sodium deoxycholate. The activity of this enzyme was stimulated 20-fold to an activity of 100 to 120 µmoles of Pi per mg of protein per hour by either phosphatidylserine or phosphatidylglycerol. The effect of the fluidity of the hydrocarbon region of the phospholipid bilayers on this re-activation of (Na + K)-ATPase was systematically examined. Fatty acyl chains of known length and varying saturation were substituted on the phosphatidylglycerol moiety and the influence of temperature on the degree of re-activation was investigated. Discontinuities in Arrhenius plots of (Na + K)-ATPase activity were found and compared with the gel-to-liquid-crystalline transitions of these substituted phosphatidylglycerols as measured in a differential scanning calorimeter. The temperature at which the Arrhenius plot discontinuities occurred were from 1° to 8° lower than the initial rise of the main endothermic peak for the series: dimyristoyl-, dipalmitoyl-, and distearoylphosphatidylglycerols. Dioleoyl-phosphatidylglycerol which does not undergo a phase transition within the experimental temperature range was found to activate at much lower concentrations than the saturated phosphatidylglycerols, and the Arrhenius plot did not show discontinuities. In contrast, bovine brain phosphatidylserine with a heterogeneous fatty acyl chain composition showed an Arrhenius plot discontinuity which was 2° higher than the midpoint of the broad endothermic peak. The relation between the discontinuities in the Arrhenius plots of the enzyme activity and the lipid phase transitions is discussed. It is suggested that some of the discontinuities represent the completion of melting (upper limit for a broad endothermic transition), whereas others represent the beginning of melting (lower limit). For completely liquid membranes, the slopes of the Arrhenius plots are parallel and give an activation energy of approximately 15 Cal per mole. The influence of membrane fluidity was also studied by examining the effects of cholesterol at constant temperature (37°). In agreement with the above findings, cholesterol, which is known to reduce the fluidity of phospholipid fatty acyl chains, inhibits phospholipid-stimulated (Na + K)-ATPase activity. The inhibition is complete, however, only with saturated phospholipids. Partial inhibition is obtained with unsaturated phospholipids. These results are discussed in relation to phase transitions in phospholipid bilayers and biomembranes and the activity of membrane-bound enzymes. A role of cholesterol in controlling the activity of membrane-bound enzymes is suggested. Implications for protein-lipid interactions in membranes are also considered.

Selective membrane toxicity of the polyene antibiotics: studies on lecithin membrane models (liposomes).

In the absence of sterol, amphotericin B at 5 x 10(-6) M caused maximum marker release from the saturated dipalmitoyl lecithin liposomes, minimum release from the unsaturated dioleoyl lecithin liposomes, and an in-between response from egg lecithin liposomes. Nystatin at 2.5 to 4.0 x 10(-5) M induced appreciable marker release from all three types of sterol-free liposomes. The amphotericin B- and nystatin-induced permeability changes in dipalmitoyl lecithin liposomes were drastically suppressed by the incorporation of cholesterol or stigmasterol (with identical Delta5 sterol nuclei), but were unaffected by the incorporation of ergosterol or 5,7-cholestadien-3beta-ol (with identical Delta5,7 sterol nuclei). The nystatin sensitivity of dioleoyl lecithin liposomes remained low after the incorporation of cholesterol or stigmasterol, but was greatly enhanced by the incorporation of ergosterol or 5,7-cholestadien-3beta-ol. Digitonin, a compound known to interact specifically with membrane sterol, induced marker release from liposomes in proportion to the amount of either cholesterol or ergosterol incorporated; epicholesterol did not sensitize to digitonin. These results lead to the following conclusions: (i) polyene-induced permeability alteration in model membrane systems is effected by the composition of membrane phospholipid fatty acyl chains; (ii) the distribution of double bonds in the sterol nucleus is related to the selective toxicity of the polyenes toward natural sterol-containing membranes; and (iii) polyenes differ in membrane selectivity.

The lipids of paramyxoviruses: A comparative study of Sendai and Newcastle disease viruses

The lipids of two paramyxoviruses, NDV-B1 and Sendai virus (propagated in ovo), were analyzed by thin-layer and gas-liquid chromatography. Both viruses had relatively large amounts of phosphatidylethanolamine and phosphatidylserine and relatively small amounts of sphingomyelin and lecithin. Analysis of fatty acid methyl esters revealed that Sendai virus had 50% more unsaturated acids than did NDV, whereas long-chain saturates accounted for 40% of the total fatty acids of the NDV envelope. Glycolipids were detected in both viruses; in the case of NDV, these were hydrolyzed and the sugars characterized by gas-liquid chromatography. Galactose, mannose, and glucose were present in molar ratios of 7:1:1, and the glycolipids were tentatively identified as ceramide hexosides. It is suggested that changes in polar groups and acyl chains of viruses propagated in homolog membranes are determined by structural proteins of the viral envelope. Differences in fatty acyl chain composition and to a lesser extent, polar groupings, may account for the pleomorphism and other biological properties of lipid-containing viruses.