Species Of Phosphatidylglycerol Research Articles

Chilling sensitivity of Arabidopsis thaliana with genetically engineered membrane lipids.

Upon transfer of a genetically engineered Escherichia coli gene for glycerol-3-phosphate acyltransferase (plsB) to Arabidopsis thaliana (L.) Heynh., the gene is transcribed and translated into an enzymatically active polypeptide. This leads to an alteration in fatty acid composition of membrane lipids. From these alterations it is evident that the enzyme is located mainly inside the plastids. The amount of saturated fatty acids in plastidial membrane lipids increased. In particular, the fraction of high-temperature melting species of phosphatidylglycerol is elevated. These molecules are thought to play a crucial role in determining chilling sensitivity of plants. An increase in sensitivity could be observed in the transgenic plants during recultivation after chilling treatment. Implications for the hypothesis of phosphatidylglycerol-determined chilling sensitivity are discussed.

The Role of Acyl Lipids in Reconstitution of Lipid-Depleted Light-Harvesting Complex II from Cold-Hardened and Nonhardened Rye

The role of acyl lipids in the in vitro stabilization of the oligomeric form of light-harvesting complex II of winter rye (Secale cereale L. cv Muskateer) grown at 5 or 20 degrees C was investigated. Purified light-harvesting complex II was enzymically delipidated to various extents by treatment with the following lipolytic enzymes: phospholipase C, phospholipase A(2), and galactolipase. Complete removal of phosphatidylcholine had no effect on the stability of the oligomeric form, whereas the removal of phosphatidylcholine plus phosphatidylglycerol caused a decrease in the ratio of oligomeric:monomeric forms from 1.86 +/- 0.17 to 0.85 +/- 0.17 and 3.51 +/- 0.82 to 0.81 +/- 0.29 for purified cold-hardened and nonhardened light-harvesting complex II, respectively, with no change in free pigment content. Incubation of delipidated cold-hardened or nonhardened light-harvesting complex with purified thylakoid phosphatidylglycerol containing trans-Delta(3)-hexadecenoic acid resulted in 48% reconstitution of the oligomeric form on a total chlorophyll basis with an oligomer:monomer of about 1.90. Incubation in the presence of di- 16:0 or di- 18:1 phosphatidylglycerol, phosphatidylcholine, monogalactosyldiacylglyceride, or digalactosyldiacylglyceride caused no oligomerization, but rather a further destabilization of the monomeric form. These lipid-dependent structural changes were correlated with significant changes in the 77K fluorescence emission spectra for purified light-harvesting complex II. We conclude that the stabilization of the supramolecular organization of light-harvesting complex II from rye is specifically dependent upon molecular species of phosphatidylglycerol containing trans-Delta(3)-hexadecenoic acid.

Polar lipids of non-alkaliphilic Halococci

Until recently, only one species of Halococcus has been recognized, namely, H. morrhuae, but a large number of extremely halophilic non-alkaliphilic cocci have now been isolated from hypersaline habitats in Spain and classified into four phenons (A–D); one of the phenon D strains has been classified as a new species, Halococcus saccharolyticus. Examination of the lipids of H. saccharolyticus and four strains of phenons A–C showed the presence in all of them of C 20-C 20 and C 20-C 25 diether molecular species of phosphatidylglycerophosphate (PGP), phosphatidylglycerol (PG) and phosphatidic acid (PA); a monounsaturated isoprenoid C 20-C 20 (phytanyl-phytenyl) species of PGP; a sulfated diglycosyl diphytanylglycerol (S-DGD) with structure 2,3-diphytanyl-1-(6-HSO 3-mannosyl-1-2-glucosyl)-glycerol, which is identical to the S-DGD-1 in Haloferax mediterranei, a phosphoglycolipid (P-TGD) tentatively identified as a phytanylphytenyl -(H 2PO 3-galactosyl-mannosyl-glycosyl)-glycerol, and two unidentified glycolipids present only in traces. No phosphatidylglycerosulfate (PGS) was detected in any of the strains examined. This pattern of lipids appears to be characteristic of the strains of Halococcus from salterns in Spain, but studies of a larger number and variety of Haloccus are necessary to establish this conclusion with certainty.

Partition of parinaroylphosphatidylethanolamines and parinaroylphosphatidylglycerols in immiscible phospholipid mixtures

Partitioning of two parinaroyl phosphatidylethanolamines and two parinaroyl phosphatidylglycerols between solid and fluid phase phospholipids was examined. Fluorescence quantum yields and fluorescence polarization measurements were used to calculate K p s/t, the solid to fluid partition coefficient of each probe (Sklar, L.A., Miljanich, G.P. and Dratz, E.A. (1979) Biochemistry 18, 1707–1716). In the immiscible mixture dipalmitoylphosphatidylcholine and dilinoleylphosphatidylcholine, both 1-palmitoyl-2- trans-parinaroylphosphatidylethanolamine and 1-palmitoyl-2- trans-parinaroylphosphatidylglycerol partitioned preferentially into solid phase lipid with mean K p s/t values (calculated from quantum yields) of 3.4 ± 1.5 and 2.1 ± 0.7, respectively. In contrast, 1-oleoyl-2- cis-parinaroylphosphatidylethanolamine and 1-oleoyl-2- cis-parinaroylphosphatidylglycerol partitioned preferentially into fluid phase lipid in the same model system with mean K p s/t values (calculated from quantum yields) of 0.44 ± 0.26 and 0.16 ± 0.07, respectively. Fluorescence polarization data on the same four parinaroyl phospholipids in mixtures of solid-phase dimyristoylphosphatidyl ethanolamine and fluid-phase dilinoleoylphosphatidylglycerol were similar to those obtained in the immiscible phosphatidylcholine system, demonstrating that the partitioning of these probes is not strongly dependent on head group. Knowledge of the partition properties of these fluorescent probes is relevant to use of these probes in investigation of the phase behavior of Escherichia coli inner membrane lipids, since phosphatidylethanolamine and phosphatidylglycerol species account for approximately 95% of these lipids.

Molecular species profiles of acidic phospholipids in lung fractions of adult and perinatal rabbits

The molecular species of phosphatidylglycerol (PG) and phosphatidylinositol (PI) in pulmonary surfactant and membrane fractions of adult and perinatal rabbit lungs were analyzed by high-performance liquid chromatography of the dinitrobenzoyl derivatives of the diacylglycerols (DGs), derived from the two acidic phospholipids. The PG in both surfactant and membrane fractions of adult lungs consisted mainly of the 16:0/16:0 species, followed in order by 16:0/18:1 and 16:0/18:2 species. In contrast, the prominent molecular species of PI in the membrane fractions were 18:0/20:4 and 16:0/18:1, while surfactant PI consisted mainly of 16:0/18:1 and 16:0/18:2, containing only 3% of 16:0/16:0. In the perinatal rabbit lungs, a compositional change between surfactant PG and PI was found, i.e., an increase in PG and a decrease in PI. The molecular species compositions of PG and PI in the perinatal lungs were generally the same as those observed in the adult lungs. It should, therefore, be noted that the species profiles of surfactant PG and PI, particularly in the content of 16:0/16:0 and 18:0/20:4, are not similar, but distinctly different from each other in both adult and developing lungs. Therefore, the present results strongly suggest two possibilities; (1) both acidic phospholipids which appear in pulmonary surfactant may originate from different pools of CDP-DGs having different molecular species; and /or (2) surfactant PG and PI may be synthesized by individual enzymes having different substrate specificities for different CDP-DGs in alveolar type II cells.

Molecular species of phosphatidylglycerol from leaves of various Citrus species.

Phosphatidylglycerol (PG) is a phospholipid characteristic of chloroplasts of higher plants. Molecular species of PG isolated from leaves of 7 Citrus species were examined and grouped into 5 classes. More than 90% of the total molecules were of the prokaryotic type synthesized in chloroplasts. Fatty acid compositions (sn-1/sn-2) of the major molecular species were 18:1/16:1 (26–47% of the total molecules), 18:1/16:0 (11–35%), and 16:0/16:1 (10–22%), which were all prokaryotic. Molecular species with 18:1 at sn-1 were characteristic of Citrus leaf PG. Unsaturated prokaryotic molecular species of (18:1, 18:2, and 18:3)/(16:0 and 16:1) accounted for 65–82%, and saturated ones of (16:0 and 18:0)/(16:0 and 16:1) for 19–32%.

Effects of water stress on the molecular species composition of polar lipids from Vigna unguiculata L. leaves

Two Vigna unguiculata L. varieties, one drought-sensitive (IT-83D), and one drought-resistant (Epace) were subjected to water stress by withholding watering. At moderate water deficits, leaf polar lipid contents decreased in the sensitive variety and increased in the resistant one. At severe stress, lipid content was sharply reduced in both varieties. The degree of unsaturation in monogalactosyl-diacylglycerol (MGDG) and diglactosyl-diacylglycerol (DGDG) slightly increased in the resistant variety when subjected to moderate water stress, and this was due to an increase in the dilinolenoyl molecular species (18:3/18:3). At severe water deficits, in both varieties, the sharp decrease in dilinolenoyl-MGDG and dilinolenoyl-DGDG was responsible for the breakdown of these two galactolipid classes. All the molecular species of phosphatidylglycerol (PG) containing trans-hexadecenoic acid (16:1t) were severely reduced by drought stress, this reduction being related to a parallel increase in the 16:0-containing molecular species. This phenomenon was more pronounced in the susceptible variety. Whereas in the sensitive variety, phosphatidylcholine (PC) amount per leaf dry weight decreased with drought, in the resistant variety, PC amount increased, at all water potentials. This increase was also accompanied by an augmentation of all the molecular species containing linolenic acid (18:3).

Spontaneous vesiculation of large multilamellar vesicles composed of saturated phosphatidylcholine and phosphatidylglycerol mixtures

The influence of temperature and ionic strength on the vesiculation properties of large multilamellar vesicles containing various proportions of dimyristoylphosphatidylglycerol has been investigated. It is shown that at low ionic strengths preformed large multilamellar vesicles composed of dimyristoylphosphatidylcholine and dimyristoylphosphatidylglycerol (7:3) on incubation at the gel to liquid-crystalline transition temperature (Tc approximately 23 degrees C) spontaneously vesiculate to form predominantly unilamellar systems with a mean diameter of 120 nm. Such vesiculation is not observed for incubations at temperatures appreciably above or below Tc, and is also inhibited by higher ionic strengths. Stable large multilamellar vesicles are formed, however, in systems containing the dioleoyl species of phosphatidylcholine or phosphatidylglycerol and also for dimyristoylphosphatidylcholine/dimyristoylphosphatidylserine mixtures. The vesiculation properties of dimyristoylphosphatidylcholine/dimyristoylphosphatidylglycerol mixtures, therefore, appear to reflect an instability in the region of the Tc driven by surface potential effects which are specific for the glycerol headgroup.

Molecular species of phosphatidylcholine and phosphatidylglycerol in rat lung surfactant and different pools of pneumocytes type II.

It is not yet completely understood how a cell is able to export specific phospholipids, like dipalmitoylphosphatidylcholine (dipalmitoyl-PC), which is secreted by pneumocytes type II, into pulmonary surfactant. The acyl species composition of [3H]PC which was synthesized in type II cells in the presence of [2-3H]glycerol resembled the species composition of PC localized in intracellular pneumocyte membranes. This species pattern was different from the pattern of PC of lamellar bodies, i.e., intracellularly stored surfactant, by a higher proportion of dipalmitoyl-PC mainly at expense of 1-palmitoyl-2-oleoyl-PC. Lamellar body PC in turn showed the same species distribution as surfactant PC. The data suggest that subcellular compartmentation and/or intracellular transfer of PC destined to storage in lamellar bodies, but not secretion of lamellar bodies, involves an enrichment of dipalmitoyl-PC and a depletion of 1-palmitoyl-2-oleoyl-PC. In contrast, the acyl species pattern of phosphatidylglycerol does not seem to undergo gross changes on the path from synthesis to secretion.

Compositional and Thermal Properties of Thylakoid Polar Lipids of Nerium oleander L. in Relation to Chilling Sensitivity

The polar lipid classes from thylakoids of Nerium oleander L. were studied with the aim of relating changes in their composition and thermal behavior with reported changes in the transition temperature of their polar lipids and chilling sensitivity of their leaves. With an increase in growth temperature, the transition temperature of phosphatidylglycerol increased from 16 degrees C to 26 degrees C, and for sulfoquinovosyldiacylglycerol from 19 degrees C to 24 degrees C. Transitions in the other lipid classes were below -10 degrees C for plants grown at both growth temperature. The major changes in the molecular species of phosphatidylglycerol, with increasing growth temperature, were an increase in 1-oleoyl-2-palmitoyl phosphatidylglycerol from 21 to 39% and a decrease in 1-oleoyl-2-trans-3-hexadecanoic phosphatidylglycerol from 51 to 25%. Although the disaturated species increased from 8 to 23%, the maximum was less than that reported for chilling-sensitive plants. There was no change in the sum of the palmitic, hexadeca-trans-3-enoic and stearic acids. Dipalmitoyl sulfoquinovosyldiacylglycerol increased from 12 to 20% and 1-linolenoyl-2-palmitoyl sulfoquinovosyldiacylglycerol decreased from 40 to 30%. It is concluded that the increase in the transition temperature of the polar lipids and the sensitivity of acclimated oleander plants to chilling could not be predicted by the absolute sum of the saturated fatty acids or disaturated molecular species in phosphatidylglycerol. The polar lipid transition appears to be a product of mixing of both high and low melting-point lipids.

Fatty Acid Specificity and Selectivity of the Chloroplast sn-Glycerol 3-Phosphate Acyltransferase of the Chilling Sensitive Plant, Amaranthus lividus

Chilling sensitivity of plants is strongly correlated with the presence of high levels of a species of chloroplast phosphatidylglycerol that contains two saturated fatty acids. The most straightforward synthetic pathway for this lipid would require the primary acylation of sn-glycerol 3-phosphate (G3P) with a saturated fatty acid (palmitic acid) rather than with oleic acid, an unsaturated acid. This selective incorporation would differ markedly from the reported properties of the chloroplast G3P acyltransferases of pea and spinach, two chilling resistant plants and thus we have studied the chloroplast G3P acyltransferase of Amaranthus lividus, a chilling sensitive plant. In contrast to our results and those of others (M. Frentzen et al. 1983 Eur J Biochem 129: 629-636 and previous work) with the pea and spinach enzymes, the amaranthus chloroplast G3P acyltranferase did not select oleic acid donors from a mixture of oleic and palmitic acid donors (either coenzyme A or acyl carrier protein thioesters). Instead the fatty acid composition of the synthesized 1-acyl G3P faithfully reflected the composition of the acyl donor mixture. However, the amaranthus enzyme did strongly select against incorporation of stearic acid. The properties of the amaranthus G3P acyltransferase are consistent with this enzyme having the major role in synthesis of the disaturated phosphatidylglycerol species.

Arrhenius plots and the involvement of thermotropic phase transitions of the thylakoid membrane in chilling impairment of photosynthesis in thermophilic higher plants

Abstract Breaks and discontinuities in Arrhenius plots of physiological and physical properties of thylakoids are not diagnostic of thermotropic lipid phase transitions of the membrane. Bulk lipid transitions, as first inferred by the membrane phase transition hypothesis, do not occur in any higher plant at chilling temperatures. Solidification of some varying, but always minor, fraction of the total membrane lipid does take place. However, the presence of minor domains of solid thylakoid membrane lipid at chilling temperatures is not unique to chilling sensitive plants but is also found in tolerant species. Minor solidification may in some plants, or groups of plants, be controlled by the specific molecular species of phosphatidylglycerol only recently investigated. In plants containing little, or no, phosphatidylglycerol with this positional distribution of fatty acids, other yet unknown constituents of the membrane must fill a similar function, since DSC thermograms indicate minor solidification also in isolated, unperturbed thylakoids from chilling tolerant species. However, chilling induced phase transitions, or other perturbations, of the thylakoid membrane are not the reason for the chilling lability of net photosynthesis in the intact plant. This conclusion follows from detailed comparison between photosynthetic membranes isolated from prechilled plants and the effects of chilling exposure on CO2 fixation of the whole plant. Damage at the level of the thylakoid membrane does occur, although not to the extent where it can account for the proportionally much larger damage to CO2 fixation.

Enzymatic bases for the fatty acid positioning in phospholipids of Brevibacterium ammoniagenes

Positional distribution of fatty acids in phospholipids from Brevibacterium ammoniagenes was analyzed to find that phosphatidylethanolamine consisted mainly of 1-saturated acyl 2-unsaturated acyl species while phosphatidylglycerol consisted mainly of 1-unsaturated acyl 2-saturated acyl species. Three acyltransferase systems were characterized in a membrane preparation—the acylations of glycerophosphate, 1-acyl-glycerophosphate, and 2-acyl-glycerophosphate—which appeared to be catalyzed by different enzymes. The distribution of fatty acids in the phosphatidylethanolamine molecule was not correlated simply with the specificities of these enzymes, but the relatively high specificity for palmitoyl-CoA of the glycerophosphate acyltransferase system to form 2-acyl-glycerophosphate, followed the relatively high specificity for oleoyl-CoA of the 2-acyl-glycerophosphate acyltransferase system, provided a basis for producing the major molecular species of phosphatidylglycerol.

Phosphatidylglycerol and Chilling Sensitivity in Plants

The hypothesis that molecular species of thylakoid phosphatidylglycerol containing two saturated fatty acids (disaturated phosphatidylglycerol) confer chilling sensitivity upon plants was tested by analyzing the fatty acid composition of phosphatidylglycerols isolated from leaves of a range of plants expected to have different sensitivities to chilling temperatures.;Saturated' fatty acids (palmitate plus stearate plus hexadeca-trans-3-enoate) as a proportion of total phosphatidylglycerol fatty acids varied from 51 to 80 mole per cent in the plants analyzed but appeared to be rigidly fixed for a given plant species, being unaffected by leaf maturity or by environment.Hexadeca-trans-3-enoate occurred only at the sn-2 position, whereas C-18 fatty acids occurred only at the sn-1 position of thylakoid phosphatidylglycerol. Therefore, the proportion of disaturated molecular species could be predicted accurately from the total fatty acids of phosphatidylglycerol.Disaturated molecular species accounted for <25% of the total phosphatidylglycerol from leaves of chilling-resistant plants and for 50 to 60% of the phosphatidylglycerol in leaves from some of the most chilling-sensitive plants. However, not all chilling-sensitive plants contained high proportions of disaturated phosphatidylglycerol; solanaceous and other 16:3-plants and C(4) grasses may be important exceptions. Nonetheless, proportions of disaturated phosphatidylglycerol increased concomitantly with increasing chilling sensitivity of plants within a genus.

Production of specifically deuterium labelled dioleoyl phospholipid species in gram quantities: A convenient synthesis of [C[ 11- 2H 2]oleic acid

A relatively straightforward large scale (gram quantity) synthesis of oleic acid specifically labelled with deuterium ( 2H) at the 11 position ([C 11 −2H 2]oleic acid) is described. This synthesis is a modified version of the procedure of Tucker et al. (J. Labelled Compd., 7(1971)137) and involves the coupling of [C 2 −2H 2] nonanal with methyl 9-chlorononanoate via a Wittig reaction. The 2H-labelled nonanal is produced in greater than 75% yield. The coupling reaction results in a 60–70% yield (based on the aldehyde) which contains 95% of the cis (oleic acid) isomer. The subsequent synthesis of 1,2-[C 11 −2H 2] dioleoyl- sn-glycero-3-phosphorylcholine ([C 11 −2H 2]DOPC) yields a compound which exhibits a convenient −2H-NMR quadrupolar splitting (∼ 6 KHz at 20°C). Similarly labelled dioleoyl species of phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylglycerol (PG) and phosphatidic acid (PA) are easily derived from the [C 11- 2H 2]DOPC. The dioleoyl phosphatidylethanolamine ([C 11- 2H 2]DOPE) shows similar bilayer to hexagonal (H 11) transition characteristics as unlabelled DOPE, and this transition can be conveniently monitored by 2H-NMR techniques.

Microsomal Phospholipid Molecular Species Alterations during Low Temperature Acclimation in Dunaliella

A detailed analysis of the low temperature-induced alterations of Dunaliella salina (UTEX 1644) microsomal membrane lipids was carried out. Microsomal membranes were isolated from cells grown at 30 degrees C, from cells shifted to 12 degrees C for 12 hours, and from cells acclimated to 12 degrees C. Fatty acid analyses of the major lipid classes demonstrated significant changes in the fatty acid composition of phosphatidylcholinemine (PE) and phosphatidylglycerol (PG) but not phosphatidylcholine (PC) during the initial 12 hours at low temperature. These changes did not entail enhanced desaturation of linoleic acid. Subsequent to 12 hours, the proportions of linolenic acid increased in all phospholipids.Molecular species analyses of the phospholipids demonstrated that the most immediate changes following a shift to low temperature were limited to several molecular species of PE and PG. The changes observed in PE included a decrease in C(30) species and concomitant increases in C(34) and C(36) species. Compositional changes associated with PG entailed the emergence of a new molecular species (18:1/18:1) not found at 30 degrees C. The retailoring of molecular species resulted in an increase in the number of species having two unsaturated acyl chains and did not reflect a simple enhancement of desaturase activity as suggested by the fatty acid analysis. We conclude that the initial alterations in response to low temperature stress involve discrete changes in certain molecular species. These and further alterations of molecular species following acclimation to low temperature would appear to augment increases in acyl chain desaturation as a means of modifying membrane properties in response to low temperature stress.

Chloroplast Phospholipid Molecular Species Alterations during Low Temperature Acclimation in Dunaliella

The alterations in chloroplast phospholipid acyl chain composition and phospholipid molecular species composition of Dunaliella salina (UTEX 1644) were monitored during acclimation to low temperature. Chlorophyll fluorescence yield, an indicator of chloroplast membrane stability, was used as a physical means of following the acclimation process.Minor alterations in phospholipid acyl chain composition were evident within 36 hours of shifting the cells from 30 to 12 degrees C. Between 36 and 60 hours, pronounced changes in the acyl chain composition of phosphatidylglycerol (PG) were observed. Changes in the acyl chain composition of phosphatidylcholine (PC) did not occur until sometime after 60 hours.Alterations in the phospholipid molecular species during acclimation were also examined. The pattern of change observed in PC molecular species, namely a decrease in species having one saturated chain (16:0) paired with a C(18) acyl chain and a concomitant increase in species having two unsaturated C(18) acyl chains, suggests that molecular species changes augment fatty acid compositional changes as a mean of adapting to low temperature. The molecular species of PG were found to change abruptly between 36 and 60 hours following a shift to low temperature. During this time, a dramatic alteration in the threshold temperature of thermal denaturation of the photosynthetic apparatus, as measured by chlorophyll fluorescence, also occurred. Lipid compositional changes other than those associated with PG were negligible during this time. This strongly suggests that a correlation exists between the molecular species composition of PG and the thermal stability of the photosynthetic membrane.

Effect of pH, mono- and divalent cations on the mixing of phosphatidylglycerol with phosphatidylcholine. A monolayer (π, Δ [formula omitted]) and fluorescence study

The mixing of various molecular species of phosphatidylglycerol and phosphatidylcholine differing in their acyl chain lengths has been studied both in monolayers (π, Δ V), and in water dispersions (fluorescence polarization) with varying pH and ionic strength of the aqueous phase and in the presence of the divalent cations Mg 2+ and Ca 2+. In dilauroylphosphatidylglycerol/dipalmitoylphosphatidylcholine mixtures, both in monolayers and in water dispersions, no phase separation was detected at pH 2.9 where phosphatidylglycerol was protonated. With dipalmitoylphosphatidylglycerol/dipalmitoylphosphatidylcholine mixtures, in monolayers and at the same pH, no phase separation was detected for surface pressures below π = 40 mN · m −1 . In monolayers, and under ionic conditions such that phosphatidylglycerol was ionized (pH 5.6, 10 mM NaCl) miscibility was observed with dilauroylphosphatidylglycerol and dipalmitoylphosphatidylcholine and also with dipalmitoylphosphatidylglycerol and dilauroylphosphatidylcholine. Varying the ionic strength did not alter the miscibility of these lipids. The divalent cations Mg 2+ and Ca 2+ did not modify that of dilauroylphosphatidylglycerol with dilauroylphosphatidylcholine or with dipalmitoylphosphatidylcholine. Both in monolayers and in water dispersions, dipalmitoylphosphatidylglycerol and dilauroylphosphatidylcholine appeared to be at least partly miscible, in the presence of magnesium. Only in the presence of calcium and at high surface pressure might the monolayer data account for phase separation between these two lipids. The data presented demonstrate the existence of strong cohesive forces between phosphatidylcholine and phosphatidylglycerol with a marked influence of the former on the physical state of the latter. From an analysis of the Δ V data, it is suggested that intrafacial hydrogen bonds may play a significant role in stabilizing phosphatidylcholine/phosphatidylglycerol mixtures.

Lipid-phase transition of phosphatidylglycerol in Acholeplasma laidlawii membranes studied with phospholipase A2.

Phospholipase A2 was applied to follow the lipid phase transition of phosphatidylglycerol in the membrane of Acholeplasma laidlawii. The conclusions were identical with those obtained with physicochemical techniques. In addition, it was shown that phosphatidylglycerol undergoes the lipid phase transition in the same temperature range as the bulk of the membrane lipid; phase segregation between various molecular species of phosphatidylglycerol occurs; exchange of this phospholipid between rigid and fluid domains is a slow, temperature-dependent process; and phosphatidylglycerol-protein interactions do occur at temperatures above that of the lipid phase transition.

31P NMR studies of oriented phospholipid multilayers

The motional properties of various well-defined species of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylglycerol, as well as phospholipids from natural sources, were investigated in oriented multibilayer systems employing 31P NMR. Particular hydrocarbon phase transition transition temperature T c. The effective chemical shift anisotropy observed for hydrated phospholipids is relatively insensitive to the occurrence of gel-liquid-crystalline phase transitions, whereas the dipolar broadening experienced by the phosphate phosphorus in the nonproton decoupled spectra increases dramatically below T c. It is shown that the basic features of the results obtained may be explained by a simple model where rapid axial rotation ( τ r ⪡ 10 −5 sec) of the entire phospholipid molecule and rapid lateral diffusion occur above T c, whereas below T c the axial rotation remains, but the lateral diffusion is restricted. A theory is presented that accounts for the angular dependence of the linewidths of the 31P NMR spectra of the oriented lipid systems in the gel and liquid-crystalline phase, using a second-moment formalism.