Structured Phospholipids Research Articles

Enzymatic synthesis of ω-3 fatty acids-based structured phospholipids: A novel solvent-free preparation approach and its catalytic mechanism

ω-3 fatty acids-based phospholipids (ω-3-PLs) exhibit higher bioavailability within organisms and stability compared to polyunsaturated fatty acids in their neutral forms. In this study, ω-3 fatty acids enriched partial acylglycerols (ω-3-AGs) were produced from hydrolysis of algal oil firstly. The effects of hydrolysis processing parameters such as enzyme type, enzyme loading, oil-water ratio, reaction temperature, and time were evaluated. Subsequently, ω-3-PLs were prepared via interesterification of ω-3-AGs with PLs catalyzed by PLA1. When monoacylglycerols (MAGs) reached 60% in partial acylglycerols, the interesterification reaction showed a marked improvement, leading to the achievement of the optimal final ω-3-PLs content of 38.93%. Using molecular docking techniques to speculate on the catalytic mechanism, the results indicate that MAGs exhibit an affinity of up to −6.33 kcal/mol with PLA1, verifying their critical role in the interesterification process.

Novel reaction systems for catalytic synthesis of structured phospholipids.

Phospholipids are distinctive, adaptable molecules that are crucial to numerous biological systems. Additionally, their various architectures and amphiphilic characteristics support their unrivaled crucial functions in scientific and industrial applications. Due to their enormous potential for use in the fields of medicine, food, cosmetics, and health, structured phospholipids, which are modified phospholipids, have garnered increased attention. Traditional extraction methods, however, are pricy, resource-intensive, and low-yielding. The process of enzyme-catalyzed conversion is effective for producing several types of structured phospholipase. However, most frequently employed catalytic procedures involve biphasic systems with organic solvents, which have a relatively large mass transfer resistance and are susceptible to solvent residues and environmental effects due to the hydrophobic nature of phospholipids. Therefore, the adoption of innovative, successful, and environmentally friendly enzyme-catalyzed conversion systems provides a new development route in the field of structured phospholipids processing. Several innovative catalytic reaction systems are discussed in this mini-review, including aqueous-solid system, mixed micelle system, water-in-oil microemulsion system, Pickering emulsion system, novel solvent system, three-liquid-phase system, and supercritical carbon dioxide solvent system. However, there is still a glaring need for a thorough examination of these systems for the enzymatic synthesis of structural phospholipids. In terms of the materials utilized, applicability, benefits and drawbacks, and comparative effectiveness of each system, this research establishes further conditions for the system's selection. To create more effective biocatalytic processes, it is still important to build green biocatalytic processes with improved performance. KEY POINTS: • The latest catalytic systems of phospholipase D are thoroughly summarized. • The various systems are contrasted, and their traits are enumerated. • Different catalytic systems' areas of applicability and limitations are discussed.

Highly effective synthesis of novel structured phospholipid emulsifiers using magnetically recyclable Fe3O4@SiO2/M (M = Zn or Al) composite

It is of great importance to develop a most efficient, recyclable, and ecofriendly process to produce novel structured phospholipid emulsifiers. Herein, innovative medium-chain structured phospholipid (MCSPL) emulsifiers were synthesized through transesterification of soybean lecithins with medium-chain fatty acids (MCFAs) promoted by Zn- or Al-incorporated Fe3O4@SiO2, denoted by Fe3O4@SiO2/M (M = Zn or Al). Resultingly, Fe3O4@SiO2/M (M = Zn or Al) exhibited the most superior reactivity with 97.1% or 88.7% MCFA incorporation to other benchmark catalysts and also had excellent magnetic separability and recyclability. Noticeably, targeted MCSPLs possessed almost more superior emulsifying properties to other phospholipid emulsifiers, and had potential for use as oil–in–water emulsifiers. Conclusively, the present findings demonstrate that transesterification promoted by Fe3O4@SiO2/M (M = Zn or Al) can be a promising approach for green, economic, and highly effective synthesis of novel dual-function phospholipid emulsifiers with bioactive and emulsifying properties in food, pharmaceutical, and cosmetic industries.

Progress & Prospect of Enzyme-Mediated Structured Phospholipids Preparation

In recent years, structured phospholipids (SPLs), which are modified phospholipids (PLs), have attracted more attention due to their great potential for application in the field of pharmacy, food, cosmetics, and health. SPLs not only possess enhanced chemical, physical and nutritional properties, but also present superior bioavailability in comparison with other lipid forms, such as triacylglycerols, which make SPLs become more competitive carriers to increase the absorption of the specific fatty acids in the body. Compared with chemical-mediated SPLs, the process of enzyme-mediated SPLs has the advantages of high product variety, high substrate selectivity, and mild operation conditions. Both lipases and phospholipases can be used in the enzymatic production of SPLs, and the main reaction type contains esterification, acidolysis, and transesterification. During the preparation, reaction medium, acyl migration, water content/activity, substrates and enzymes, and some other parameters have significant effects on the production and purity of the desired PLs products. In this paper, the progress in enzymatic modification of PLs over the last 20 years is reviewed. Reaction types and characteristic parameters are summarized in detail and the parameters affecting acyl migration are first discussed to give the inspiration to optimize the enzyme-mediated SPLs preparation. To expand the application of enzyme-mediated SPLs in the future, the prospect of further study on SPLs is also proposed at the end of the paper.

Acidolysis of phospholipids with medium-chain fatty acids over M-SBA-15 (M = Zn, Al) silicas as efficient solid catalysts.

Efficient and sustainable production of structured phospholipids (SPLs) enriched in medium-chain fatty acids (MCFAs) in a heterogeneous manner is crucial for their potential applications in functional foods and drugs. Herein, for the first time, Zn- and Al-incorporated SBA-15 silicas were prepared by the coprecipitation method and further researched for catalytic synthesis of MCFA-enriched SPLs through acidolysis reaction of natural phospholipids with capric or caprylic acid. The as-prepared Zn- and Al-incorporated SBA-15 samples exhibited superior catalytic activities under mild experimental conditions (50 °C, 6h) to commercial homogeneous Lewis acids and benchmark enzymes. Correspondingly, the capric acid and caprylic acid incorporations were respectively achieved up to ~40.25 ± 0.40% (or 35.08 ± 0.09%) and 37.26 ± 0.38% (or 33.02 ± 0.13%) for Zn- (or Al-) incorporated SBA-15 catalyst. Moreover, various methods such as scanning electron microscopy with energy-dispersive X-ray spectrometry, ultraviolet-visible diffuse reflectance spectroscopy and pyridine-Fourier transform infrared spectroscopy were utilized to characterize the two catalysts in order to elucidate the possible structure-performance relationship. Accordingly, the above-mentioned satisfactory results are most probably due to the well-ordered mesostructures and large amounts of active Lewis acid sites existing in the investigated materials. Noticeably, the two catalysts featured good separation and excellent recyclability as well. The Zn- and Al-incorporated SBA-15 catalysts studied in this work might shed light on novel, sustainable and economic alternatives for effective SPL production to diminish the applications of conventional homogeneous catalysts and biocatalysts in food industries. © 2022 Society of Chemical Industry.

Efficient Synthesis of Structured Phospholipids Containing Short-Chain Fatty Acids over a Sulfonated Zn-SBA-15 Catalyst.

Catalytic production of structured phospholipids (SPLs) containing short-chain fatty acids (SCFAs) in an efficient heterogeneous manner is of great importance from the standpoint of food engineering. Herein, a bifunctionalized sulfonated Zn-SBA-15 catalyst was studied for SPL synthesis through interesterification of soybean lecithin with ethyl propionate or methyl butyrate. Various characterization techniques such as pyridine Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet-visible diffuse reflectance spectroscopy were conducted to determine the physicochemical properties, so as to build the possible structure-reactivity relationship of the catalyst. In screening tests with commercial Amberlyst-15 or other SBA-15-type materials, the as-prepared sample showed promising catalytic performance probably owing to its mesoporous structure and cooperative role of Brönsted and Lewis acid sites. Notably, the sample was easily separated and recycled without obvious deactivation. In general, the investigated catalyst was regarded as one of the promising alternatives to otherwise expensive biocatalysts for SCFA-containing SPL production.

Characteristics and emulsifying properties of structured phospholipids from palm pressed fiber and omega-3 fatty acid concentrates from by-products of fish processing by enzymatic acidolysis.

The synthesis of structured phospholipids (SPLs) containing ω-3 fatty acids was carried out through enzymatic acidolysis reactions using lipase from Rhizomucor miehei between palm pressed fiber phospholipids (PPF PL) with four ω-3 fatty acid concentrates as different acyl sources. The purity of SPLs increased compared to original PPF PLs. The degree of ω-3 fatty acid incorporation to the SPLs was different that depended on the sources of acyl. The highest degree of incorporation was in PE (phosphatidylethanolamine). The phenomenon of acyl migration of EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) was found from the sn-1 to the sn-2 position of the PE. This acyl migration occurred at all four SPLs. Modification of PLs made better emulsifying properties for oil in water emulsion system, compared to PPF PL. The increase in the HLB (hydrophilic-lipophilic balance) value, EAI (emulsifying activity index), and ESI (emulsion stability index) of SPLs compared to PPF PL was supposed to relate to an increase in polarity. The composition of more polar PLs (PC/phosphatidylcholine, PE, PG/phosphatidylglycerol, and PA/phosphatidic acid) in the four SPLs is higher than that of PPF PL. The sources of acyl also affected the emulsifying properties of four SPLs.

Efficient Production of Medium-Chain Structured Phospholipids over Mesoporous Organosulfonic Acid-Functionalized SBA-15 Catalysts

It is highly desirable that efficient recoverable heterogeneous catalysts should be developed to replace the costly biocatalysts used in producing structured phospholipids (SPLs) with medium-chain fatty acids (MCFAs). Thus, mesoporous propyl and phenyl sulfonic acid-functionalized SBA-15 materials synthesized via surface modification methods were investigated for the soybean lecithin interesterification with methyl caprate or caprylate. The physicochemical properties of the synthesized solid acids were deeply studied by small-angle X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared and pyridine adsorption, etc. to build the possible structure–performance relationships. The results revealed that amounts of organosulfonic acid groups were successfully grafted onto the SBA-15 support, and most of the surface acid sites contained in the as-prepared organic–inorganic hybrid samples were assigned as strong Brӧnsted acid sites. Notably, the functionalized SBA-15 materials exhibited promising catalytic behaviors in producing MCFA-enriched SPLs under mild conditions (40 °C, 6 h) when compared with commercial Amberlyst-15 and typical phospholipases or lipases, mostly due to their high surface area, ordered structure and adequate Brӧnsted acid sites. Besides, the as-prepared materials could be easily recycled five times without obvious deactivation. This work might shed light on alternative catalysts for SPL production instead of the costly enzymes.

Dead-end complex, lipid interactions and catalytic mechanism of microsomal glutathione transferase 1, an electron crystallography and mutagenesis investigation

Microsomal glutathione transferase 1 (MGST1) is a detoxification enzyme belonging to the Membrane Associated Proteins in Eicosanoid and Glutathione Metabolism (MAPEG) superfamily. Here we have used electron crystallography of two-dimensional crystals in order to determine an atomic model of rat MGST1 in a lipid environment. The model comprises 123 of the 155 amino acid residues, two structured phospholipid molecules, two aliphatic chains and one glutathione (GSH) molecule. The functional unit is a homotrimer centered on the crystallographic three-fold axes of the unit cell. The GSH substrate binds in an extended conformation at the interface between two subunits of the trimer supported by new in vitro mutagenesis data. Mutation of Arginine 130 to alanine resulted in complete loss of activity consistent with a role for Arginine 130 in stabilizing the strongly nucleophilic GSH thiolate required for catalysis. Based on the new model and an electron diffraction data set from crystals soaked with trinitrobenzene, that forms a dead-end Meisenheimer complex with GSH, a difference map was calculated. The map reveals side chain movements opening a cavity that defines the second substrate site.

Synthesis and Identification of AceDoxyPC, a Protectin-Containing Structured Phospholipid, Using Liquid Chromatography/Mass Spectrometry.

Fatty acids have many health benefits in a great variety of diseases ranging from cardiovascular to cerebral diseases. For instance, docosahexaenoic acid (DHA), which is highly enriched in brain phospholipids, plays a major role in anti-inflammatory or neuroprotective pathways. Its effects are thought to be due, in part, to its conversion into derived mediators such as protectins. 1-Lyso,2-docosahexaenoyl-glycerophosphocholine (LysoPtdCho-DHA) is one of the physiological carrier of DHA to the brain. We previously synthesized a structured phosphatidylcholine to mimic 1-lyso,2-docosahexaenoyl-glycerophosphocholine, named AceDoPC® (1-acetyl,2-docosahexaenoyl-glycerophosphocholine), that is considered as a stabilized form of the physiological LysoPtdCho-DHA and that is neuroprotective in experimental ischemic stroke. Considering these, the current study aimed at enzymatically oxygenate DHA contained within AceDoPC® to synthesize a readily structured oxidized phospholipid containing protectin DX (PDX), thereafter named AceDoxyPC (1-acetyl,2-PDX-glycerophosphocholine). Identification of this product was performed using liquid chromatography/tandem mass spectrometry. Such molecule could be used as a bioactive mediator for therapy against neurodegenerative diseases and stroke.

Specific uptake of DHA by the brain from a structured phospholipid, AceDoPC®

Docosahexaenoic acid (DHA; 22:6 ω-3) is highly enriched in the brain and is required for proper brain development and function. Its deficiency has been shown to be linked with the emergence of neurological diseases. Dietary ω-3 fatty acid supplements including DHA have been suggested to improve neuronal development and enhance cognitive functions. Findings suggested that DHA is better incorporated into the brain when esterified at the sn- 2 position of a lysophosphatidylcholine (LysoPC-DHA). AceDoPC® is a structured phospholipid or acetyl-LysoPC-DHA. As previously shown for LysoPC-DHA, AceDoPC® is a specific and preferred carrier of DHA to the brain. When AceDoPC® was injected to rats that were subjected to an ischemic stroke, it prevents the extension of brain lesions. Regarding the essential role of DHA for cerebral functions, targeting the brain with specific carriers of DHA might provide novel therapeutic approaches to neurodegenerative diseases.

AceDoPC, a structured phospholipid to target the brain with docosahexaenoic acid

AceDoPC ® is a structured phospholipid or acetyl-LysoPC-DHA made to prevent docosahexaenoic acyl migrating from the sn -2 to sn -1 position of the phospholipid, however keeping the main physical-chemical properties of LysoPC-DHA. As previously shown for LysoPC-DHA, AceDoPC ® allows DHA crossing a re-constituted blood-brain barrier with higher efficiency than non-esterified DHA or PC-DHA. When injected to blood of rats, AceDoPC ® is processed within the brain to deliver DHA to phosphatidyl-choline and -ethanolamine. When injected to rats following the induction of an ischemic stroke, AceDoPC ® prevents the extension of brain lesions more efficiently than DHA. Overall, these properties make AceDoPC ® a promising phospholipid carrier of DHA to the brain.

Enzymatic synthesis and modification of structured phospholipids: recent advances in enzyme preparation and biocatalytic processes.

Phospholipids (PLs) containing specific polar head groups and fatty acids, artificially synthesized from a complex mixture of natural PLs, have considerable industrial applications. The biocatalytic approaches to synthesizing structured PLs are of great interest because the enzymes used show high selectivity and performance under mild conditions, leading to the generation of products that cannot easily be obtained by chemical catalysis. Although the limited supply of phospholipases (e.g., phospholipase D) has thus far been an obstacle to the widespread use of enzymatic processing, recent advances in enzyme preparation have opened up various applications for PL modification. In this review, attempts to increase the productivity and utility of microbial phospholipases and lipases are presented. We also summarize recent developments in enzyme-catalyzed modification of PLs, focusing particularly on the relevant reactions, bioreactor design, and novel proof-of-concept experiments.

Efficient Docosahexaenoic Acid Uptake by the Brain from a Structured Phospholipid.

Docosahexaenoic acid (DHA) is the main essential omega-3 fatty acid in brain tissues required for normal brain development and function. An alteration of brain DHA in neurodegenerative diseases such as Alzheimer's and Parkinson's is observed. Targeted intake of DHA to the brain could compensate for these deficiencies. Blood DHA is transported across the blood-brain barrier more efficiently when esterified at the sn-2 position of lyso-phosphatidylcholine. We used a structured phosphatidylcholine to mimic 2-docosahexaenoyl-lysoPC (lysoPC-DHA), named AceDoPC (1-acetyl,2-docosahexaenoyl-glycerophosphocholine), that may be considered as a stabilized form of the physiological lysoPC-DHA and that is neuroprotective in experimental ischemic stroke. The aim of the present study was to investigate whether AceDoPC is a relevant delivery form of DHA to the brain in comparison with other forms of the fatty acid. By combining in vitro and in vivo experiments, our findings report for the first time that AceDoPC is a privileged and specific carrier of DHA to the brain, when compared with DHA-containing PC and non-esterified DHA. We also show that AceDoPC was hydrolyzed, in part, into lysoPC-DHA. Ex vivo autoradiography of rat brain reveals that DHA from AceDoPC was localized in specific brain regions playing key roles in memory, thoughts, and cognitive functions. Finally, using molecular modeling approaches, we demonstrate that electrostatic and lipophilic potentials are distributed very similarly at the surfaces of AceDoPC and lysoPC-DHA. Our findings identify AceDoPC as an efficient way to specifically target DHA to the brain, which would allow potential preventive and therapeutic approaches for neurological diseases.

Characterization of the Biophysical Properties of Novel Saturated Bis(monoacylglycero)phosphate Analogues

Bis(monoacylglycero)phosphate (BMP18:1) is an uniquely structured anionic phospholipid found in enriched concentrations in the internal membranes of the lysosome and late endosome.1 BMP18:1, differs from typical phospholipids, possessing two glycerol moieties each with a single oleoyl acyl-chain as well as an atypical sn-1:sn-1′ stereoconfiguration. It has been suggested that the unusual structure of BMP18:1 plays a role in lipid and protein trafficking, as well as glycosphingolipid degradation.2,3 Dimyristoyl-BMP (BMP14:0) and dipalmitoylphosphatidylcholine (DPPC) undergo a phase transition from the gel to liquid crystalline phase at 42 °C, whereas the phosphatidylcholine with myristoyl acyl-chains, dimyristoylphosphatidylcholine (DMPC), undergoes a gel to liquid crystalline phase transition at 23 °C. It is therefore of interest to investigate the thermotropic phase behavior of saturated BMP analogues. Temperature dependent 2H-NMR was used to characterize analogues of BMP with lauroyl, myristoyl, palmitoyl, or stearoyl acyl-chains. First moment (M1) analyses of 2H-NMR spectra can be used to monitor the gel to liquid crystalline phase transition. The phase transition temperature for each BMP analogue was found to be higher than the phosphatidylcholine consisting of the corresponding acyl-chain. BMP18:0 was studied under three different buffer conditions to determine the effects of pH and ionic strength on the phase transition.1. Kobayshi et al., J. Biol. Chem., 2002, 277, 32157.2. Gruenberg, Curr. Opin. Cell Biol., 2003, 15, 382.3. Schulze, Kolter, and Sandhoff, BBA, 2009, 1793, 674.

Nanoscale Structured Phospholipid Polymer Brush for Biointerface

To prepare the biomaterial surface having both lubricity and biocompatibility, we aimed to prove the mechanism of the resistance of friction and protein adsorption with grafting polymer. We prepared poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) grafted layer using an atom transfer radical polymerization (ATRP) method, which had the advantage of controlling surface structures on nanoscale. From the results of surface characterization, it was confirmed that the thickness of the PMPC grafted layer was 4-10 nm and the conformation of the PMPC grafted layer was brushlike. We investigated the friction properties in air and in water with an atomic force microscopy (AFM). The friction coefficients of the PMPC brush layers were decreased dramatically in water and the resistance of friction depended on the thickness of the PMPC brush layer. We also investigated the protein adhesion properties by measuring the force-distance curves using the AFM cantilever immobilized with a bovine serum albumin (BSA). The adhesion force between the BSA and the PMPC brush layers were markedly reduced and the resistance of the BSA adhesion depended on the thickness of the PMPC brush layer. For resisting both friction and protein adsorption in water, it was a key factor to keep the thick hydrated layer made by the elongated hydrophilic PMPC brush chains.

Continuous production of structured phospholipids in a packed bed reactor with lipase from Thermomyces lanuginosa

AbstractThe possibilities of producing structured phospholipids between soybean phospholipids and caprylic acid by lipase‐catalyzed acidolysis were examined in continuous packedbed enzyme reactors. Acidolysis reactions were performed in both a solvent system and a solvent‐free system with the commercially immobilized lipase from Thermomyces lanuginosa (Lipozyme TL IM) as catalyst. In the packed bed reactors, different parameters for the lipase‐catalyzed acidolysis were elucidated, such as solvent ratio (solvent system), temperature, substrate ratio, residence time, water content, and operation stability. The water content was observed to be very crucial for the acidolysis reaction in packed bed reactors. If no water was added to the substrate during reactions under the solvent‐free system, very low incorporation corporation of caprylic acid was observed. In both solvent and solvent‐free systems, acyl incorporation was favored by a high substrate ratio between acyl donor and phospholipids, a longer residence time, and a higher reaction temperature. Under certain conditions, the incorporation of around 30% caprylic acid can be obtained in continuous operation with hexane as the solvent.

Enzymatic synthesis of structured lipids.

Structured lipids (SLs) are defined as lipids that are modified chemically or enzymatically in order to change their structure. This review deals with structured triacylglycerols (STGs) and structured phospholipids (SPLs). The most typical STGs are MLM-type STGs, having medium chain fatty acids (FAs) at the 1- and 3-positions and a long chain fatty acid at the 2- position. MLM-type STGs are synthesized by: 1) 1,3-position-specific lipase-catalyzed acyl exchange of TG with FA or with FA ethylester (FAEt); 2) 1,3-position-specific lipase-catalyzed acylation of glycerol with FA, giving symmetric 1,3-diacyl-sn-glycerol, followed by chemical acylation at the sn-2 position, and; 3) 1,3-position-specific lipase-catalyzed deacylation of TG, giving 2-monoacylglycerol, followed by reacylation at the 1- and 3-positions with FA or with (FAEt). Enzymatic preparation of SPLs requires: 1) acyl group modification, and 2) head group modification of phospholipids. Acyl group modification is performed using lipases or phospholipase A2-mediated transesterification or ester synthesis to introduce arbitrary fatty acid to phospholipids. Head group modification is carried out by phospholipase D-catalyzed transphosphatidylation. A wide range of compounds can be introduced into the polar head of phospholipids, making it possible to prepare various SPLs.

Biologically addressable monolayer structures formed by templates of sulfur-bearing molecules

We demonstrate that the combined application of Langmuir-Blodgett and self-assembly techniques allows the fabrication of patterns with contrasting surface properties on gold substrates. The process is monitored using fluorescence microscopy and surface plasmon spectroscopy and microscopy. These structures are suitable for the investigation of biochemical processes at surfaces and in ultrathin films. Two examples of such processes are shown. In the first example, the structures are addressed through the binding of a monoclonal antibody to a peptide. This demonstrates the formation of self-assembled monolayers by cysteine-bearing peptides on gold, and the directed binding of proteins to the structured layers. A high contrast between specific and unspecific binding of proteins is observed by the patterned presentation of antigens. Such films possess considerable potential for the design of multichannel sensor devices. In the second example, a structured phospholipid layer is produced by controlled self-assembly from vesicle solution. The structures created--areas of phospholipid bilayer, surrounded by a matrix of phospholipid monolayer--allow formation of a supported bilayer which is robust and strongly bound to the gold support, with small areas of free-standing bilayer which very closely resemble a phospholipid cell membrane.

Further studies of the role of surfactant in premature rupture of the membranes

OBJECTIVE: The purpose of this study was to assess the hypothesis that surface-active phospholipid (i.e., amniotic surfactant) plays a major role in maintaining the mechanical integrity of the chorioamniotic sac. STUDY DESIGN: Three studies were designed using chorioamniotic sacs from normal term deliveries. First, it was demonstrated how the extreme hydrophobicity (and lubricity) of amniotic and chorionic epithelium could be greatly reduced by incubating the membrane with bile salts, which react with surface-active phospholipid. Second, hydrophobic probes were used under epifluorescence microscopy to identify any structured surface-active phospholipid. Third, electron microscopy was used to investigate the ultrastructure, by means of a novel fixation procedure that does not destroy hydrophobic interfaces. RESULTS: Both morphologic studies confirmed planar structures of oligolamellar surface-active phospholipid running parallel to the membrane that contained lamellar bodies. CONCLUSION: These sheets of surface-active phospholipid could be very cohesive within the planes, thus improving tensile strength while promoting shearing between planes to provide the type of lubrication afforded by graphite whose ultrastructure they closely resemble. (AM J OBSTET GYNECOL 1994;170:195-201.)