Cholesterol interactions with tetracosenoic acid phospholipids in model cell membranes: role of the double-bond position

Phases and phase transitions of the phosphatidylcholines

LIPIDAT (http://www.lipidat.chemistry.ohio-state.edu) is an Internet accessible, computerized relational database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior and molecular structures. Here, a review of the data subset referring to phosphatidylcholines is presented together with an analysis of these data. This subset represents ca. 60% of all LIPIDAT records. It includes data collected over a 43-year period and consists of 12,208 records obtained from 1573 articles in 106 different journals. An analysis of the data in the subset identifies trends in phosphatidylcholine phase behavior reflecting changes in lipid chain length, unsaturation (number, isomeric type and position of double bonds), asymmetry and branching, type of chain-glycerol linkage (ester, ether, amide), position of chain attachment to the glycerol backbone (1,2- vs. 1,3-) and head group modification. Also included is a summary of the data concerning the effect of pressure, pH, stereochemical purity, and different additives such as salts, saccharides, amino acids and alcohols, on phosphatidylcholine phase behavior. Information on the phase behavior of biologically derived phosphatidylcholines is also presented. This review includes 651 references.

Cholesterol's interfacial interactions with sphingomyelins and phosphatidylcholines: hydrocarbon chain structure determines the magnitude of condensation

Cholesterol's interfacial interaction with different sphingomyelins and phosphatidylcholines has been investigated using a Langmuir film balance. The average molecular area of cholesterol/sphingomyelin (SM) or cholesterol/phosphatidylcholine (PC) mixed monolayers was determined as a function of film composition from the force-area isotherms measured at 24 degrees C. In contrast to previous results [Lund-Katz, S., Laboda, H. M., McLean, L. R., & Phillips, M. C. (1988) Biochemistry 27, 3416-3423], little difference was observed in equimolar cholesterol's "condensing effect" of SMs compared to PCs when their phase state was similar and when their hydrocarbon structural differences were minimized. For PCs, this meant that one acyl chain had to be long and capable of assuming an extended conformation and thus configurationally similar to the long-chain base of SM. This condition facilitated strong van der Waals attractive interactions with cholesterol's planar steroid ring and was satisfied when the sn-1 acyl chain of PC was either myristate or palmitate. Under these conditions, the structural requirements of the sn-2 chain of PC were mitigated. For instance, at equimolar cholesterol, almost no difference was observed in the apparent molecular area condensations of 1-palmitoyl-2-oleoyl-PC and 1-palmitoyl-2-arachidonoyl-PC at surface pressures between 10 and 40 mN/m. In contrast, the apparent molecular area condensations of dioleoyl-PC and diarachidonoyl-PC were substantially reduced under identical experimental conditions. The results are discussed in terms of the relative importance of phospholipid/sphingolipid hydrocarbon and headgroup structure in determining the extent of interaction with cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of an essential fatty acid deficiency on the phospholipid composition in anterior pituitary membranes

The effects of an essential fatty acid deficient diet were investigated on the phospholipid fatty acids of several membrane fractions of the rat anterior pituitary, the secretion of which is known to be partly dependent on the membrane phospholipidic constituents. In standard dietary conditions, arachidonic acid (20:4n-6) and its elongation product, adrenic acid (22:4n-6), were the two main polyunsaturated fatty acids in all fractions studied. In rats deprived of EFA for 6 weeks after weaning, the levels of both 20:4n-6 and 22:4n-6 were not changed in microsomal + plasma membrane and nuclear fractions, whereas they were decreased in heavy mitochondrial and light mitochondrial fractions. The present data suggest a mechanism of compensation between membrane fractions which may preferentially preserve 20:4n-6 and 22:4n-6 in discrete membrane fractions.

Phospholipid studies of marine organisms: 26. Interactions of some marine sterols with 1-stearoyl-2-oleoyl phosphatidylcholine (SOPC) in model membranes

The thermotropic behavior of multilamellar vesicles (MLV) composed of different mole fractions of various marine sterols and 1-stearoyl-2-oleoyl phosphatidylcholine (SOPC) was examined by differential scanning calorimetry (DSC), and was compared to pure SOPC as well as their mixtures with cholesterol. The marine sterols investigated were capable of interacting with the phospholipid bilayers. Upon addition of marine sterols, the apparent transition temperature (Tm) of SOPC decreased significantly. Desmosterol (cholesta-5,24-dien-3 beta-ol) had the least interaction with SOPC, as reflected by the larger delta H values of its mixtures with the phospholipid. Fucosterol (24-ethylcholesta-5,24(28)-dien-3 beta-ol) showed a non-linear trend as the mole percent of the sterol increased. Mixtures of sutinasterol (24R-24-ethyl-26,26-dimethylcholesta-7,25(27)-dien-3 beta-ol) with SOPC had similar enthalpy values to cholesterol. The shape of the SOPC/marine sterol endotherm and their delta H values were not identical when liposomes prepared by dialysis were compared to MLV.

Cholesterol does not remove the gel-liquid crystalline phase transition of phosphatidylcholines containing two polyenoic acyl chains

Homoacid (single-acid) phosphatidylcholines containing two linoleate (18:2), arachidonate (20:4), or docosahexaenoate (22:6) chains were dispersed in water to form multilamellar vesicles. The influence of cholesterol on the gel to liquid phase transitions was studied by differential scanning calorimetry (DSC). The pure dipolyenoic phosphatidylcholines exhibited very broad endothermic transitions (widths of 28 to 38 C degrees at scanning rates of 5 C degrees/min) in the temperature range of about -80 degrees C to -30 degrees C. The mixing of cholesterol into the phospholipids in proportions up to 50 mol% had little effect on the temperatures, widths or enthalpy changes associated with the phase transitions. The data suggest that cholesterol does not interfere with the packing of these lipids in the gel state, possibly because the packing is already irregular or because the solubility of cholesterol in these lipids is low, or both.