Individual Phospholipid Molecular Species Research Articles

Cardiac lipidomic profiles in mice undergo changes from fetus to adult

AimsLipids are essential cellular components with many important biological functions. Disturbed lipid biosynthesis and metabolism has been shown to cause cardiac developmental abnormality and cardiovascular diseases. In this study, we aimed to investigate the composition and the molecular profiles of lipids in mammalian hearts between embryonic and adult stages and uncover the underlying links between lipid and cardiac development and maturation. Materials and methodsWe collected mouse hearts at the embryonic day 11.5 (E11.5), E15.5, and the age of 2 months, 4 months and 10 months, and performed lipidomic analysis to determine the changes of the composition, molecular species, and relative abundance of cardiac lipids between embryonic and adult stages. Additionally, we also performed the electronic microscopy and RNA sequencing in both embryonic and adult mouse hearts. Key findingsThe relative abundances of certain phospholipids and sphingolipids including cardiolipin, phosphatidylglycerol, phosphatidylethanolamine, and ceramide, are different between embryonic and adult hearts. Such lipidomic changes are accompanied with increased densities of mitochondrial membranes and elevated expression of genes related to mitochondrial formation in adult mouse hearts. We also analyzed individual molecular species of phospholipids and sphingolipids, and revealed that the composition and distribution of lipid molecular species in hearts also change with development. SignificanceOur study provides not only a lipidomic view of mammalian hearts when developing from the embryonic to the adult stage, but also a potential pool of lipid indicators for cardiac cell development and maturation.

Lipid profiling of barley root in interaction with Fusarium macroconidia

Fusarium is the major causal agent of Fusarium head blight (FHB) in several cereal crops. Macroconidia, the asexual form of Fusarium, can infect the roots and aerial parts of plants. The response of cereal to attacks by Fusarium has been investigated at transcriptomic and metabolomic level, but there are no reports of root lipidomic assays carried out during Fusarium-root interaction. In order to determine how root phospholipids contribute to that interaction, we performed a lipidomics-based ESI-MS/MS assay coupled with a statistical analysis. It was found that phospholipid and galactolipid levels were not modified during early pathogen response, although some individual phospholipid molecular species did undergo significant changes. In plants exposed to macroconidia there was a rapid and transient increase in the phosphatidylcholine (36:4-PC) molecular species, in comparison with the control. By contrast, there was a decrease in lysophosphatidylcholine (16:0-, 18:2- and 18:3-LPC) levels. Furthermore, a phospholipase assay and the measurement of endogenous phytohormone levels through the use of fluorescent lipids and liquid chromatography-tandem mass spectrometry, revealed an increase in phospholipase A (PLA) activity, as well as in the endogenous amounts of Jasmonic acid (JA) and Salicylic acid (SA). The results indicate that barley root is able to modulate the glycerolipid fatty acid composition during the early response to Fusarium, suggesting a particular pathogen-sensing mechanism that could be useful to understand the role of lipids in plant-pathogen interactions.

Uncovering the lipidic basis for the preparation of functional nicotinic acetylcholine receptor detergent complexes for structural studies.

This study compares the lipid composition, including individual phospholipid molecular species of solubilized nAChR detergent complexes (nAChR-DCs) with those of the bulk lipids from their source, Torpedo californica (Tc) electric tissue. This lipidomic analysis revealed seventy-seven (77) phospholipid species in the Tc tissue. Analysis of affinity-purified nAChR-DCs prepared with C-12 to C-16 phospholipid analog detergents alkylphosphocholine (FC) and lysofoscholine (LFC) demonstrated that nAChR-DCs prepared with FC12, LFC14, and LFC16 contained >60 phospholipids/nAChR, which was more than twice of those prepared with FC14, FC16, and LFC12. Significantly, all the nAChR-DCs lacked ethanolamine and anionic phospholipids, contained only four cholesterol molecules, and a limited number of phospholipid molecular species per nAChR. Upon incorporation into oocytes, FC12 produce significant functionality, whereas LFC14 and LFC16 nAChR-DCs displayed an increased functionality as compared to the crude Tc membrane. All three nAChR-DCs displayed different degrees of alterations in macroscopic activation and desensitization kinetics.

Differential changes in galactolipid and phospholipid species in soybean leaves and roots under nitrogen deficiency and after nodulation.

The availability of nitrogen (N) to plants has a profound impact on carbohydrate and protein metabolism, but little is known about its effect on membrane lipid species. This study examines the changes in galactolipid and phospholipid species in soybean as affected by the availability of N, either supplied to soil or obtained through Bradyrhizobium japonicum nodulation. When N was limited in soil, the content of galactolipids, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacyglycerol (DGDG), decreased drastically in leaves, while a smaller decrease of DGDG was observed in roots. In both leaves and roots, the overall content of different phospholipid classes was largely unchanged by N limitation, although some individual phospholipid molecular species did display significant changes. Nodulation with Bradyrhizobium of soybean grown in N-deficient soil resulted in a large increase in levels of plastidic lipid classes, MGDG, DGDG, and phosphatidylglycerol, along with smaller increases in non-plastidic phospholipids in leaves. Nodulation also led to higher levels of phospholipids in roots without changes in root levels of MGDG and DGDG. Overall, N availability alters lipid content more in leaves than roots and more in galactolipids than phospholipids. Increased N availability leads to increased galactolipid accumulation in leaves, regardless of whether N is supplied from the soil or symbiotic fixation.

Oxidative lipidomics of hyperoxic acute lung injury: mass spectrometric characterization of cardiolipin and phosphatidylserine peroxidation

Reactive oxygen species have been shown to play a significant role in hyperoxia-induced acute lung injury, in part, by inducing apoptosis of pulmonary endothelium. However, the signaling roles of phospholipid oxidation products in pulmonary endothelial apoptosis have not been studied. Using an oxidative lipidomics approach, we identified individual molecular species of phospholipids involved in the apoptosis-associated peroxidation process in a hyperoxic lung. C57BL/6 mice were killed 72 h after exposure to hyperoxia (100% oxygen). We found that hyperoxia-induced apoptosis (documented by activation of caspase-3 and -7 and histochemical terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling staining of pulmonary endothelium) was accompanied by nonrandom oxidation of pulmonary lipids. Two anionic phospholipids, mitochondria-specific cardiolipin (CL) and extramitochondrial phosphatidylserine (PS), were the two major oxidized phospholipids in hyperoxic lung. Using electrospray ionization mass spectrometry, we identified several oxygenation products in CL and PS. Quantitative assessments revealed a significant decrease of CL and PS molecular species containing C(18:2), C(20:4), C(22:5), and C(22:6) fatty acids. Similarly, exposure of mouse pulmonary endothelial cells (MLEC) to hyperoxia (95% oxygen; 72 h) resulted in activation of caspase-3 and -7 and significantly decreased the content of CL molecular species containing C(18:2) and C(20:4) as well as PS molecular species containing C(22:5) and C(22:6). Oxygenated molecular species were found in the same two anionic phospholipids, CL and PS, in MLEC exposed to hyperoxia. Treatment of MLEC with a mitochondria-targeted radical scavenger, a conjugate of hemi-gramicidin S with nitroxide, XJB-5-131, resulted in significantly lower oxidation of both CL and PS and a decrease in hyperoxia-induced changes in caspase-3 and -7 activation. We speculate that cytochrome c driven oxidation of CL and PS is associated with the signaling role of these oxygenated species participating in the execution of apoptosis and clearance of pulmonary endothelial cells, thus contributing to hyperoxic lung injury.

Imaging of lipid species by MALDI mass spectrometry

Recent developments in MALDI have enabled direct detection of lipids as intact molecular species present within cellular membranes. Abundant lipid-related ions are produced from the direct analysis of thin tissue slices when sequential spectra are acquired across a tissue surface that has been coated with a MALDI matrix. The lipid-derived ions can often be distinguished from other biomolecules because of the significant mass defect that these ions present due to the large number of covalently bound hydrogen atoms in hydrophobic molecules such as lipids. Collisional activation of the molecular ions can be used to determine the lipid family and often structurally define the molecular species. Specific examples in the detection of phospholipids, sphingolipids, and glycerolipids are presented with images of mouse brain and kidney tissue slices. Regional distribution of many different lipid molecular species and Na+ and K+ attachment ions often define anatomical regions within the tissues.

Circulating ether‐lipids as an early marker of POAG

Abstract Purpose Neuronal tissues such as the retina contain high amounts of particular phospholipids named “ether‐lipids”. Since abnormal blood levels of ether‐lipids have been associated with several neurological disorders, we wanted to check whether ether‐lipid levels were modified and associated with the severity of POAG. Methods Blood samples were collected from 41 healthy subjects and 64 POAG patients. Following lipid extraction from erythrocytes, total phospholipids including ether‐lipids were isolated using silica cartridges. The fatty acid profile of phospholipids was determined using capillary column gas chromatography (GC). The individual molecular species of phospholipids and ether‐lipids were quantified by tandem liquid chromatography‐mass spectrometry. Results The levels of ether‐lipids were significantly decreased in glaucoma patients and especially the choline ether‐lipid sub‐class. The Mean Deviation (MD) value from Humphrey perimetry was negatively correlated to erythrocyte levels of total choline ether‐lipids (r²=0.99). The linear regression model predicted that total choline ether‐lipid levels started to decrease about 20 years prior to clinical symptoms. Conclusion Although the mechanisms responsible for the reduction of erythrocyte levels of ether‐lipids in POAG patients remains unclear, the known functions of ether‐lipids in the protection against oxidative stress make these results very consistent with the pathogenesis of glaucoma.

Lipidomics of cellular and secreted phospholipids from differentiated human fetal type II alveolar epithelial cells

Maturation of fetal alveolar type II epithelial cells in utero is characterized by specific changes to lung surfactant phospholipids. Here, we quantified the effects of hormonal differentiation in vitro on the molecular specificity of cellular and secreted phospholipids from human fetal type II epithelial cells using electrospray ionization mass spectrometry. Differentiation, assessed by morphology and changes in gene expression, was accompanied by restricted and specific modifications to cell phospholipids, principally enrichments of shorter chain species of phosphatidylcholine (PC) and phosphatidylinositol, that were not observed in fetal lung fibroblasts. Treatment of differentiated epithelial cells with secretagogues stimulated the secretion of functional surfactant-containing surfactant proteins B and C (SP-B and SP-C). Secreted material was further enriched in this same set of phospholipid species but was characterized by increased contents of short-chain monounsaturated and disaturated species other than dipalmitoyl PC (PC16:0/16:0), principally palmitoylmyristoyl PC (PC16:0/14:0) and palmitoylpalmitoleoyl PC (PC16:0/16:1). Mixtures of these PC molecular species, phosphatidylglycerol, and SP-B and SP-C were functionally active and rapidly generated low surface tension on compression in a pulsating bubble surfactometer. These results suggest that hormonally differentiated human fetal type II cells do not select the molecular composition of surfactant phospholipid on the basis of saturation but, more likely, on the basis of acyl chain length.

Quantitative determination of phospholipid compositions by ESI-MS: effects of acyl chain length, unsaturation, and lipid concentration on instrument response

Electrospray ionization-mass spectrometry (ESI-MS) is a very promising tool for the analysis of phospholipid compositions, but is hampered by the fact that not all molecular species are detected with equal efficiency. We studied this and other issues that need to be taken into account to obtain truly quantitative compositional data. The key findings were as follows: First, the instrument response for both saturated and unsaturated phospholipid species decreased with increasing acyl chain length. This effect became increasingly prominent with increasing overall lipid concentration. Second, the degree of acyl chain unsaturation also had a significant effect on instrument response. At the highest concentration studied (10 pmol/microl), polyunsaturated species gave 40% higher intensity than the fully saturated ones. The effect of unsaturation diminished and nearly disappeared with progressive dilution. Third, the instrument response for the different head group classes varied markedly depending on the infusion solvent used. Notably, inclusion of ammonia in the infusion solvent eliminated sodium adduct formation in the positive ion mode, thus greatly simplifying the interpretation of the spectra. The fact that instrument response is dependent on many structural features, overall lipid concentration, solvent composition, and instrument settings makes it necessary to include several internal standards for each phospholipid class to obtain accurate data. Preferably, both unsaturated and saturated standards should be used. Finally, we quantified the major phospholipid classes of BHK cells using ESI-MS. The data agreed closely with those obtained with thin-layer chromatography and phosphorus analysis. This study indicates that quantitative compositional data can be obtained with ESI-MS, provided that proper attention is paid to experimental details, particularly the choice of internal standards.

Quantitation of individual phospholipid molecular species by UV absorption measurements

To validate the utility of on-line measurements of UV absorption for the direct quantitation of individual phospholipid molecular species isolated by reverse-phase HPLC, we synthesized 37 different individual molecular species of diacyl choline glycerophospholipids. UV absorbance response factors (integrate UV absorbance/nmole phospholipid) were calculated for all diacyl, alkenylacyl, and alkylacyl species by injecting varying amounts of the purified molecular species in the 2-100 nmole range and integrating the UV absorbance at 203 nm. There was excellent agreement between the results of the quantitation of individual molecular species determined by measurements of phospholipid mass in HPLC fractions with that based on measurements of total integrated UV absorption and the use of absorbance response factors. The on-line quantitation of individual phospholipid molecular species by UV absorption measurement should prove useful as an adjunct to other techniques of phospholipid quantitation, as a means to assist in the identification of individual molecular species in complex biologic mixtures, and as a stand-alone approach to phospholipid quantitation to facilitate studies of the metabolism of individual species particularly when coupled with radiolabeling techniques.

Phospholipid profiles in the oral yeast Candida

Individual molecular species of phospholipids can now be readily detected using fast atom-bombardment mass spectrometry (FAB MS). The aim was to obtain detailed information on individual molecular species of Candida phospholipids using FAB MS. Lipids were extracted from Candida isolates and prepared for FAB MS analysis in negative-ion mode. Each isolate yielded several hundred anion peaks. The major anion peaks consistent with the presence of phospholipids included those of mass/charge (m/z) 836, 743, 715, 744 and 834 tentatively identified as phosphatidylethanolaminePE(43:5), phosphatidylglycerolPG(34:3), PG(32:3), PE(36:1) and PE(43:5). Major peaks consistent with the presence of car☐ylate anions were of m/z 241, 253, 255, 277, 279, 281, 283, and 307 putatively identified asC 15:0, C 16:1, C 16:0, C 18:3, C 18:2, C 18:1, C 18:0 andC 20:2 which also support the putative identifications of phospholipids. Such phospholipid profiles differ from those published for other microorganisms analysed by FAB MS. Quantitative differences were observed between different candidal species. Candida albicans may be readily differentiated from C. glabrata on the basis of its car☐ylate anions. Within species, there are quantitative differences in phospholipid profiles. Thus, Candida has a unique combination of phospholipid analogues with potential chemosystematic significance.

Phospholipid molecular species of Bacteroides

The fatty acid composition, and types of polar lipid (PL) present, have been well‐studied in Bacteroides. Nothing is known, however, of the detailed structures of individual phospholipid and molecular species. The aim of this study was to determine molecular weights and putative identities of individual phospholipid molecular species present in Bacteroides. Thirteen culture collection strains were harvested, washed and freeze‐dried. Polar lipids were extracted and separated by conventional fast atom bombardment mass spectrometry (FAB MS). For each strain, hundreds of polar lipid peaks were seen. Nineteen major anions in the range m/z 209–299 were separated. The most intense of these was consistent with the expected presence of the C15:0 anion. Other anions were attributable to saturated, mono‐unsaturated, di‐unsaturated, tri‐unsaturated and hydroxy‐carboxylate ions. Twenty‐two major anion peaks were recorded in the range m/z 505–722. These were consistent with the presence of analogues of phosphatidic acid (PA), phosphatidylethanolamine (PE) and phosphatidylglycerol (PG). The most intense peaks included those consistent with the presence of PE(30:0), PG(29:1), PG(30:1), PG(28:1), PE(31:0), PE(OH‐30:0), PG(31:1) and PE(OH‐31:0). This combination of PL molecular species is unique to Bacteroides and has not been reported in other organisms so far examined.

Phospholipid molecular species composition of developing fetal guinea pig brain.

Adequate accumulation of polyunsaturated essential fatty acids, in particular docosahexaenoic acid (22:6n-3), into membrane phospholipids is critical for optimal fetal brain development. This process is maximal during the period of rapid neurite outgrowth, neuritogenesis, which precedes the major growth phase, myelination. There is no information about differential changes during gestation to individual brain phospholipid molecular species which contain 22:6n-3. Such details of brain development would be concealed by total fatty acid analysis of isolated phospholipid classes. We have detailed phosphatidylcholine (PC) and phosphatidylethanolamine (PE) molecular species compositions in developing fetal guinea pig brain. Total brain PC concentration increased substantially between 40 and 68 (term) d of gestation, corresponding to myelination, while PE increased in a biphasic manner between 25-35 d, which was coincident with onset of neuritogenesis, and 40-68 d. Fetal brain development was accompanied by complex changes in the concentration of individual phospholipid molecular species. During early gestation (25-40 d) 22:6n-3 was enriched in both PC and PE sn-1 16:0 molecular species. However, between 40 d and term there was no further increase in brain PC 22:6n-3 content, while brain PE was significantly enriched in both PE18:1/22:6 and PE18:0/22:6. We hypothesize that accumulation of 22:6n-3 into sn-1 18:1 and 18:0 species represents establishment of a 22:6n-3-containing membrane PE pool which may be turned over more slowly than sn-1 16:0 species. Identification of specific changes in membrane phospholipids which are associated with defined events in brain development may provide a basis for assigning functional roles to individual molecular species.

Plasmalogen phospholipid hydrolysis during hypoxic injury of rabbit proximal tubules

We have identified and quantified the major species of arachidonate-containing phospholipids in proximal tubules by high performance liquid chromatographic and gas chromatographic analyses. Arachidonate was found to comprise 53% of the total mass of fatty acids esterified at the sn-2 position of ethanolamine phospholipids, and 51% of that amount resides in three plasmenylethanolamine species containing the vinyl ethers of palmitaldehyde, oleylaldehyde or stearylaldehyde at the sn-1 position. Choline phospholipids contained 21% arachidonylated species and 33% of that amount resides in a single plasmenylcholine species containing the vinyl ether of palmitaldehyde at the sn-1 position. Ten minutes of hypoxia did not cause a significant change in the total phospholipid mass of ethanolamine or choline phospholipids; however, phosphate analysis of the individual phospholipid molecular species containing esterified arachidonic acid in isolated proximal tubules demonstrated a 24% reduction in the mass of the plasmenylethanolamine molecular species with the vinyl ether of oleylaldehyde at the sn-1 position and a 35% reduction in the mass of plasmenylcholine species with palmitaldehyde at the sn-1 position. These studies underscore the pathophysiological importance of plasmalogen phospholipid hydrolysis and suggest that activation of PLA2s, which utilize endogenous proximal tubule plasmalogen substrates, may play an important role in the early generation of arachidonic acid and accompanying phospholipid catabolism during hypoxic cell injury.

Recycling of docosahexaenoic acid in rat retinas during n-3 fatty acid deficiency.

About 50% of the fatty acids in retinal rod outer segments is docosahexaenoic acid [22:6(n-3)], a member of the linolenic acid [18:3(n-3)] family of essential fatty acids. Dietary deprivation of n-3 fatty acids leads to only modest changes in 22:6(n-3) levels in the retina. We investigated the mechanism(s) by which the retina conserves 22:6(n-3) during n-3 fatty acid deficiency. Weanling rats were fed diets containing 10% (wt/wt) hydrogenated coconut oil (no n-3 or n-6 fatty acids), linseed oil (high n-3, low n-6), or safflower oil (high n-6, less than 0.1% n-3) for 15 weeks. The turnover of phospholipid molecular species and the turnover and recycling of 22:6(n-3) in phospholipids of the rod outer segment membranes were examined after the intravitreal injection of [2-3H]glycerol and [4,5-3H]22:6(n-3), respectively. Animals were killed on selected days, and rod outer segment membranes, liver, and plasma were taken for lipid analyses. The half-lives (days) of individual phospholipid molecular species and total phospholipid 22:6(n-3) were calculated from the slopes of the regression lines of log specific activity versus time. There were no differences in the turnover rates of phospholipid molecular species among the three dietary groups, as determined by the disappearance of labeled glycerol. Thus, 22:6(n-3) is not conserved through a reduction in phospholipid turnover in rod outer segments. However, the half-life of [4,5-3H]22:6(n-3) in the linseed oil group (19 days) was significantly less than in the coconut oil (54 days) and safflower oil (not measurable) groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dietary cholesterol on phosphatidylcholines and phosphatidylethanolamines in bile and gallbladder mucosa in the prairie dog

Humans with cholesterol gallstones have been reported to have alterations in the molecular species of phospholipids in bile. Both decreases in phospholipids with linoleic acid and increases in those with arachidonic acid have been found. The purpose of this study was to investigate the effect of a lithogenic diet (0.34% cholesterol) on the relative abundance of individual molecular species of phospholipids in the biliary tract of the prairie dog. In hepatic bile, cholesterol feeding resulted in increases in phospholipid species containing arachidonate and decreases in the major species containing its precursor, linoleate. In gallbladder bile of both control and cholesterol-fed animals, phospholipid species containing linoleate were significantly less abundant than in hepatic bile, suggesting that linoleoyl species were selectively absorbed by the gallbladder epithelium. This apparent uptake was significantly increased by cholesterol feeding. Phosphatidylcholines and phosphatidylethanolamines containing arachidonate were also significantly increased in the gallbladder mucosa of the cholesterol-fed animals. These increases in arachidonate-containing phospholipids in the gallbladder mucosa may contribute to the increase in gallbladder prostaglandin synthesis that precedes gallstone formation in this animal model.

Differential methylation patterns in molecular species of phosphatidylethanolamine derivatives in rat liver membranes

The appearance of individual molecular species of phospholipids in the complete sequence of the transmethylation of phosphatidylethanolamine (PE) was examined in rat liver microsomes incubated with S- adenosyl- l -|methyl- 14 C|methionine Reverse-phase HPLC analysis of phosphatidylcholine (PC), phosphatidyl- N, N-dimethylethanolamine (dimethyl-PE), or phosphatidyl- N-monomethylethanolamine (monomethyl-PE) showed that radioactivity was present in the same six principal molecules; a first group is constituted by 16:0/22:6, 16:0/20:4 and 16:0/18:2 and a second one by the homologous molecules with 18:0 instead of 16:0 at the sn-1 position of glycerol. In PC, 16:0/22:6 (23% of total radioactivity) was preponderant, and 18:0/20:4 was the lowest. The ratios cpm in PC/nmol in PE were in the order: 16:0/22:6 > 16:0/18:2 > 16:0/20:4 followed by the corresponding 18:0 molecules. On the other hand, in intermediate phospholipids, incorporation of methyl groups was most marked in 18:0/20:4 (24–27% of total). 16:0/22:6 and 16:0/18:2 were low in comparison to their relative values in PC. The ratio (18:0/20:4)/16:0/22:6) was 4.5–5.6-times higher in monomethyl-PE and dimethyl-PE than in PC. These differences were found consistently, regardless of incubation time of microsomes (2.5–60 min) and of S- adenosyl- l-methionine (AdoMet) concentration (3 or 100 μM). In liver membranes, it would therefore seem that there is a different selectivity in methyl group transfer, depending upon whether the first two steps or the third step of the reaction are considered. Side reactions, such as deacylation/reacylation, are unlikely to account for this difference, which could rather be related to the enzyme itself.

Phospholipid metabolism in roots and microsomes of sunflower seedlings: Inhibition of choline phosphotransferase activity by boron

The action of boron on phospholipid composition and synthesis in roots and microsomes from sunflower seedlings has been studied. The fatty acid composition and relative amounts of individual molecular species of phospholipids in roots and microsomes were very similar. In both the content of phospholipids was decreased and the relative levels of their component fatty acids changed by treatment with 50 ppm of boron. This concentration of boron in the culture medium was found to inhibit the in vivo [1- 14C] acetate incorporation into root lipids and that of [Me- 14C] choline into phosphatidylcholine of root microsomes. Cytidine-5-diphospho (CDP)-[Me- 14C] choline incorporation into phosphatidylcholine of isolated microsomes was also inhibited by 50 ppm of boron when present in the growth medium of seedlings. These results indicate that the decrease in phosphatidylcholine labelling from [ 14C] choline observed when root microsomes were treated with boron would be caused by a decrease in CDP-choline phosphotransferase activity.

Separation of phospholipids and individual molecular species of phospholipids by high-performance liquid chromatography.

Isocratic high-performance liquid chromatography methods are described for separating the major classes of phospholipids and for isolating the individual molecular species of phospholipids. Fractionation of a total lipid extract of rat liver on a silica column resulted in quantitative recoveries of all major phospholipids with preservation of their fatty acid composition. Rat liver phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidylserine were then each chromatographed on a C18 reverse phase column to isolate individual molecular species. Component peaks were identified by their fatty acid composition and quantitated by phosphorus determination. Using this method we found that for each of these phospholipids from 30 to 35 different molecular species can be routinely identified and reproducibly quantitated. A characteristic elution sequence of molecular species permitted their identification based upon their retention times on a reverse phase column.

47] Lipids of invertebrate photoreceptors

Publisher Summary This chapter discusses the lipids of invertebrate photoreceptors. Rhodopsin is an integral protein in the photoreceptor membrane (rod outer segment, ROS) for vertebrates and the microvillar membrane for invertebrates. Because of the strong hydrophobic nature of rhodopsin and the apparent bilayer character of the membranes, the properties of the rhodopsin should be partly dependent on the physical and chemical nature of the membrane environment and in particular on the membrane's lipid constituents. Separation procedures for individual molecular species of phospholipids are established. By adapting or modifying these methods, tlie lipid composition of microvillar membrane of octopus photoreceptor cells are discussed in this chapter.