Lipid composition of marine and estuarine invertebrates: porifera and cnidaria

Coral Lipids

Reef-building corals, recognized as cornerstone species in marine ecosystems, captivate with their unique duality as both symbiotic partners and autotrophic entities. Beyond their ecological prominence, these corals produce a diverse array of secondary metabolites, many of which are poised to revolutionize the domains of pharmacology and medicine. This exhaustive review delves deeply into the multifaceted world of coral-derived lipids, highlighting both ubiquitous and rare forms. Within this spectrum, we navigate through a myriad of fatty acids and their acyl derivatives, encompassing waxes, sterol esters, triacylglycerols, mono-akyl-diacylglycerols, and an array of polar lipids such as betaine lipids, glycolipids, sphingolipids, phospholipids, and phosphonolipids. We offer a comprehensive exploration of the intricate biochemical variety of these lipids, related fatty acids, prostaglandins, and both cyclic and acyclic oxilipins. Additionally, the review provides insights into the chemotaxonomy of these compounds, illuminating the fatty acid synthesis routes inherent in corals. Of particular interest is the symbiotic bond many coral species nurture with dinoflagellates from the Symbiodinium group; their lipid and fatty acid profiles are also detailed in this discourse. This exploration accentuates the vast potential and intricacy of coral lipids and underscores their profound relevance in scientific endeavors.

Functionally diverse front-end desaturases are widespread in the phylum Annelida

Aquatic single-cell organisms have long been believed to be unique primary producers of omega-3 long-chain (≥C20) polyunsaturated fatty acids (ω3 LC-PUFA). Multiple invertebrates including annelids have been discovered to possess methyl-end desaturases enabling key steps in the de novo synthesis of ω3 LC-PUFA, and thus potentially contributing to their production in the ocean. Along methyl-end desaturases, the repertoire and function of further LC-PUFA biosynthesising enzymes is largely missing in Annelida. In this study we examined the front-end desaturase gene repertoire across the phylum Annelida, from Polychaeta and Clitellata, major classes of annelids comprising most annelid diversity. We further characterised the functions of the encoded enzymes in selected representative species by using a heterologous expression system based in yeast, demonstrating that functions of Annelida front-end desaturases have highly diversified during their expansion in both terrestrial and aquatic ecosystems. We concluded that annelids possess at least two front-end desaturases with Δ5 and Δ6Δ8 desaturase regioselectivities, enabling all the desaturation reactions required to convert the C18 precursors into the physiologically relevant LC-PUFA such as eicosapentaenoic and arachidonic acids, but not docosahexaenoic acid. Such a gene complement is conserved across the different taxonomic groups within Annelida.

Coral Lipidome: Molecular Species of Phospholipids, Glycolipids, Betaine Lipids, and Sphingophosphonolipids

Coral reefs are the most biodiversity-rich ecosystems in the world's oceans. Coral establishes complex interactions with various microorganisms that constitute an important part of the coral holobiont. The best-known coral endosymbionts are Symbiodiniaceae dinoflagellates. Each member of the coral microbiome contributes to its total lipidome, which integrates many molecular species. The present study summarizes available information on the molecular species of the plasma membrane lipids of the coral host and its dinoflagellates (phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), ceramideaminoethylphosphonate, and diacylglyceryl-3-O-carboxyhydroxymethylcholine), and the thylakoid membrane lipids of dinoflagellates (phosphatidylglycerol (PG) and glycolipids). Alkyl chains of PC and PE molecular species differ between tropical and cold-water coral species, and features of their acyl chains depend on the coral's taxonomic position. PS and PI structural features are associated with the presence of an exoskeleton in the corals. The dinoflagellate thermosensitivity affects the profiles of PG and glycolipid molecular species, which can be modified by the coral host. Coral microbiome members, such as bacteria and fungi, can also be the source of the alkyl and acyl chains of coral membrane lipids. The lipidomics approach, providing broader and more detailed information about coral lipid composition, opens up new opportunities in the study of biochemistry and ecology of corals.

Sticholysin recognition of ceramide-phosphoethanolamine

Actinoporins are pore-forming toxins produced by sea anemones. They exert their activity by binding to the membranes of target cells. There, they oligomerize, forming cation-selective pores, and inducing cell death by osmotic shock. In the early days of the field, it was shown that accessible sphingomyelin (SM) in the bilayer is required for the activity of actinoporins. While these toxins can also act on membranes composed solely of phosphatidylcholine (PC) with a high amount of cholesterol (Chol), consensus is that SM acts as a lipid receptor for actinoporins. It has been shown that the 2NH and 3OH moieties of SM are essential for actinoporin recognition. Hence, we wondered if ceramide-phosphoethanolamine (CPE) could also be recognized. Like SM, CPE has the 2NH and 3OH groups, and a positively charged headgroup. While actinoporins have been observed to affect membranes containing CPE, Chol was always also present, with the recognition of CPE remaining unclear. To test this possibility, we used sticholysins, produced by the Caribbean Sea anemone Stichodactyla helianthus. Our results show that sticholysins can induce calcein release on vesicles composed only of PC and CPE, in absence of Chol, in a way that is comparable to that induced on PC:SM membranes.

Jellyfish from Fisheries By-Catches as a Sustainable Source of High-Value Compounds with Biotechnological Applications

The world’s population growth and consequent increased demand for food, energy and materials together with the decrease of some natural resources have highlighted the compelling need to use sustainably existing resources and find alternative sources to satisfy the needs of growing and longer-aging populations. In this review, we explore the potential use of a specific fisheries by-catch, jellyfish, as a sustainable source of high-value compounds. Jellyfish are often caught up with fish into fishing gear and nets, then sorted and discarded. Conversely, we suggest that this by-catch may be used to obtain food, nutraceutical products, collagen, toxins and fluorescent compounds to be used for biomedical applications and mucus for biomaterials. These applications are based on studies which indicate the feasibility of using jellyfish for biotechnology. Because jellyfish exhibit seasonal fluctuations in abundance, jellyfish by-catches likely follow the same pattern. Therefore, this resource may not be constantly available throughout the year, so the exploitation of the variable abundances needs to be optimized. Despite the lack of data about jellyfish by-catches, the high value of their compounds and their wide range of applications suggest that jellyfish by-catches are a resource which is discarded at present, but needs to be re-evaluated for exploitation within the context of a circular economy in the era of zero waste.

Structural foundations of sticholysin functionality

Actinoporins constitute a family of α pore-forming toxins produced by sea anemones. The soluble fold of these proteins consists of a β-sandwich flanked by two α-helices. Actinoporins exert their activity by specifically recognizing sphingomyelin at their target membranes. Once there, they penetrate the membrane with their N-terminal α-helices, a process that leads to the formation of cation-selective pores. These pores kill the target cells by provoking an osmotic shock on them. In this review, we examine the role and relevance of the structural features of actinoporins, down to the residue level. We look at the specific amino acids that play significant roles in the function of actinoporins and their fold. Particular emphasis is given to those residues that display a high degree of conservation across the actinoporin sequences known to date. In light of the latest findings in the field, the membrane requirements for pore formation, the effect of lipid composition, and the process of pore formation are also discussed.

Novel Caryophyllane-Related Sesquiterpenoids with Anti-Inflammatory Activity from Rumphella antipathes (Linnaeus, 1758)

Two previously undescribed caryophyllane-related sesquiterpenoids, antipacids A (1) and B (2), with a novel bicyclo[5.2.0] core skeleton, and known compound clovane-2β,9α-diol (3), along with rumphellolide L (4), an esterified product of 1 and 3, were isolated from the organic extract of octocoral Rumphella antipathes. Their structures, including the absolute configurations were elucidated by spectroscopic and chemical experiments. In vivo anti-inflammatory activity analysis indicated that antipacid B (2) inhibited the generation of superoxide anions and the release of elastase by human neutrophils, with IC₅₀ values of 11.22 and 23.53 μM, respectively, while rumphellolide L (4) suppressed the release of elastase with an IC₅₀ value of 7.63 μM.

Properties of a New Food Supplement Containing Actinia equina Extract

Marine species represent a great source of biologically active substances; Actinia equina (AE), an Anthozoa Cnidaria belonging to the Actinidiae family, have been proposed as original food and have already been included in several cooking recipes in local Mediterranean shores, and endowed with excellent nutraceutical potential. The aim of this study was to investigate some unexplored features of AE, through analytical screening and an in-vitro and in-vivo model. An in-vitro study, made on RAW 264.7 stimulated with H₂O₂, showed that the pre-treatment with AE exerted an antioxidant action, reducing lipid peroxidation and up-regulating antioxidant enzymes. On the other hand, the in-vivo study over murine model demonstrated that the administration of AE extracts is able to reduce the carrageenan (CAR)-induced paw edema. Furthermore, the histological damage due to the neutrophil infiltration is prevented, and this highlights precious anti-inflammatory features of the interesting food-stuff. Moreover, it was assessed that AE extract modulated nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) and The nuclear factor erythroid 2-related factor 2 (Nrf-2) pathways. In conclusion, our data demonstrated that thanks to the antioxidant and anti-inflammatory properties, AE extract could be used as a new food supplement for inflammatory pathology prevention.

Biotechnological Applications of Scyphomedusae

As people across the world live longer, chronic illness and diminished well-being are becoming major global public health challenges. Marine biotechnology may help overcome some of these challenges by developing new products and know-how derived from marine organisms. While some products from marine organisms such as microalgae, sponges, and fish have already found biotechnological applications, jellyfish have received little attention as a potential source of bioactive compounds. Nevertheless, recent studies have highlighted that scyphomedusae (Cnidaria, Scyphozoa) synthesise at least three main categories of compounds that may find biotechnological applications: collagen, fatty acids and components of crude venom. We review what is known about these compounds in scyphomedusae and their current biotechnological applications, which falls mainly into four categories of products: nutraceuticals, cosmeceuticals, biomedicals, and biomaterials. By defining the state of the art of biotechnological applications in scyphomedusae, we intend to promote the use of these bioactive compounds to increase the health and well-being of future societies.

Comparative lipidomic analysis of phospholipids of hydrocorals and corals from tropical and cold-water regions

To expand our knowledge of lipid and fatty acid (FA) biosynthesis in marine cnidarians, polar lipidomes of hydrocorals were studied for the first time and then compared with those of soft corals from tropical and boreal regions. The structure and content of FAs and molecular species of ethanolamine, choline, serine, and inositol glycerophospholipids (PE, PC, PS, and PI, respectively), and ceramide aminoethylphosphonate (CAEP) in tropical hydrocorals (Millepora platyphylla, M. dichotoma) and the cold-water hydrocoral Allopora steinegeri were determined by chromatography and mass spectrometry. All soft corals and cold-water hydrocorals are characterized by a considerable amount of C₂₀ polyunsaturated FAs (PUFAs) elongated into C₂₂ PUFAs. In the Millepora species, the high level of 22:5n-6 and 22:6n-3 against the background of the extremely low level of C₂₀ PUFAs may be explained by a high activity of rare Δ4 desaturase. In contrast to hydrocorals, soft corals are able to elongate and further desaturate C₂₂ PUFAs into C₂₄ PUFAs. Allopora and soft corals use C₂₀ PUFAs mainly for the synthesis of PE and PC. The molecular species of PS of soft corals concentrate C₂₄ PUFAs, while in Allopora and Millepora the PS molecules are mainly based on 22:4n-6 and 22:5n-6 acyl groups, respectively. Short acyl groups (C₁₄) dominate the CAEP molecules of Allopora. In all the animals compared, most molecular species of PE and PC are ether lipids, but diacyl molecular species dominate PI. Hydrocorals and tropical soft corals contain diacyl and ether PS molecules, respectively, whereas cold-water soft corals contain a mixture of these PS forms. The high similarity of the alkyl/acyl compositions indicates a possible biosynthetic relationship between PS and PI in hydrocorals. The data obtained in our study will provide a resource to further investigate the lipid metabolism in marine invertebrates.

Fatty acid biomarkers of symbionts and unusual inhibition of tetracosapolyenoic acid biosynthesis in corals (octocorallia)

Seven zooxanthellae-free species of octocorals (the genera Acanthogorgia, Acabaria, Chironephthya, Echinogorgia, Menella, Ellisella, and Bebryce) and two zooxanthellate octocorals (the genera Paralemnalia and Rumphella) were examined to elucidate their fatty acid (FA) composition. Arachidonic (about 40% of the total FA) and palmitic acids were predominant in all the species studied. Seven furan FA (F-acids) (up to 9.7%) were identified in the azooxanthellate octocorals. The main F-acids were 14,17-epoxy-15-methyldocosa-14,16-dienoic and 14,17-epoxy-15,16-dimethyldocosa-14,16-dienoic acids. In all specimens of Bebryce studeri, C(25-28) demospongic FA (about 20%) were identified. These FA reflect the presence of a symbiotic sponge in B. studeri and can be used as the specific markers for other corals. A significant difference (P < 0.01) between azooxanthellate and zooxanthellate corals was found for odd-chain and methyl-branched saturated FA, 18:1n-7, and 7-Me-16:1n-10; that indicated the presence of an advanced bacterial community in azooxanthellate corals. The zooxanthellate species were distinguished by significant amounts of 18:3n-6, 18:4n-3, and 16:2n-7 acids, which are proposed as the markers of zooxanthellae in soft corals. Contrary to the normal level of 24:5n-6 (9.4%) and 22:4n-6 (0.6%), unexpected low concentrations of 24:5n-6 (0.4%) accompanied by a high content of 22:4n-6 (up to 11.9%) were detected in some specimens. The presence of an unknown factor in octocorals, specific for n-6 PUFA, which inhibited elongation of 22:4n-6 to 24:4n-6, is conjectured.

Comparison of fatty acid compositions of azooxanthellate Dendronephthya and zooxanthellate soft coral species

Ten zooxanthellae-free Dendronephthya species , twelve zooxanthellate soft coral species of the genera Sarcophyton, Lobophytum, Cladiella, Lytophyton, Cespitularia, and Clavularia, and the hermatypic coral Caulastrea tumida were examined for the first time to elucidate the fatty acid (FA) composition of total lipids. In Dendronephthya species, the main FAs were 20:4n-6, 24:5n-6, 16:0, 18:0, 7-Me-16:1n-10, and 24:6n-3 which amounted on the average to 26.0, 12.7, 12.1, 6.0, 4.8, and 4.0% of the total FA contents, respectively. For zooxanthellate soft corals, the main FAs were 16:0 (25.7%), 20:4n-6 (18.2%), 24:5n-6 (6.2%), and 18:4n-3 (5.6%), as well as 16:2n-7, which amounted up to 11.8% in Sarcophyton aff. crassum. Corals with zooxanthellae had low contents of 24:6n-3. The significant difference (p<0.01) between azooxanthellate and zooxanthellate soft corals was indicated only for 12 of 46 FAs determined. The principal components analysis confirmed that 7-Me-16:1n-10, 17:0, 18:4n-3, 18:1n-7, 20:4n-6, 22:5n-6, 24:5n-6, and 24:6n-3 are useful for chemotaxonomy of Dendronephthya. The azooxanthellate soft corals studied were distinguished by the absence of significant depth-dependent and species-specific variations of FA composition, low content of 16:2n-7, an increased proportion of bacterial FAs, predominance of n-6 FAs connected with active preying, and a high ability for biosynthesis of tetracosapolyenoic FAs.

Polar and Neutral Lipid Composition in the Pelagic Tunicate Pyrosoma atlanticum

Structure and functioning of colonial pyrosomes are largely undescribed and their lipid characteristics have received limited attention. The aim of this paper is to fill this gap on one of the dominant species Pyrosoma atlanticum. Lipid content is tightly coupled to size and weight. Lipid composition shows a large dominance of structural polar lipids. Neutral lipids were dominated by sterols with low levels of acylglycerols and free fatty acids. Phospholipids show a dominance of PC with intermediate percentages of PE and DPG. Other constituents (PS, PI, LPC, sphingolipids) were present at lower levels. Fatty acid composition of DAG and TAG showed a dominance of saturated acids (16:0, 14:0), DHA and intermediate levels of MUFA. Phospholipids were dominated by DHA with values exceeding 30% of total FA in all categories except for PI, where lower percentages occurred. Saturated acids were second in abundance with MUFA showing intermediate concentrations. Sterols were dominated by 24-methylcholesta-5,22E-dien-3beta-ol with more than 22% of the total sterol. Cholesterol (cholest-5-en-3beta-ol) represented only 12 % of the total while 24-methylcholesta-5,24(28)E-dien-3beta-ol accounted for 11% of the total sterols. The low levels of triacylglycerols and free fatty acids, coupled with high concentrations of glycolipids and phytoplankton-derived degraded chloropigments, is evidence of a direct link with the digestive activity and substantiate the idea of a high physiological turnover as an alternative to large lipid accumulation. The fatty acid and sterol profiles are consistent with a diverse phytoplankton diet, and a strong contribution of phospholipid classes to energy needs, including locomotion.

Lipid class and fatty acid composition of the boreal soft coral Gersemia rubiformis

Total lipid, phospholipid, and FA composition and distribution of FA between polar lipids (PL) and neutral lipids (NL) were investigated in the boreal soft coral Gersemia rubiformis from the Bering Sea. The total lipids were mostly hydrocarbons and waxes (33.7%) and PL (33.1%). The content of monoalkyldiacylglycerols (9.7%) exceeded the content of TAG (6.7%). PC and PE constituted 31.4% and 25.6% of total phospholipids, respectively. Principal FA were 16:0, 16:1n-7, 18:0, 18:1n-9, 18:1n-7, 20:1n-7, 20:4n-6, 20:4n-3, 20:5n-3, 22:5n-3, 22:6n-3, 24:5n-6, and 24:6n-3. Most n-6 PUFA (52% of total FA) were associated with the PL fraction; this was especially true for arachidonic and tetracosapentaenoic acids. The NL were enriched with mono-, di-, trienoic, and n-3 PUFA. The variation in EPA levels in both NL and PL suggests an origin of this acid from lipids of diatoms consumed by the corals.

Lipid compounds of freshwater sponges: family Spongillidae, class Demospongiae

More than 100 novel, unusual and rare fatty acids, lipids and sterols have been isolated from freshwater sponges. The structures, biogenesis, synthesis and bioactivity of some lipid compounds of freshwater sponge species are reviewed.

Multibranched polyunsaturated and very-long-chain fatty acids of freshwater Israeli sponges

Very-long-chain and multibranched polyunsaturated fatty acids of three freshwater sponges, Ephydatia syriaca, Nudospongilla sp., and Cortispongilla barroisi, were studied by silver TLC, GC-MS, UV, IR, HRMS, and NMR methods. One hundred and eighty-five conventional fatty acids were identified by GC-MS, out of which five were new multibranched polyunsaturated fatty acids. The freshwater sponges belonging to the family Spongillidae (class Demospongia) were shown to contain novel di-, tri-, and tetramethyl substituted dienoic, tetraenoic, and hexaenoic fatty acids. The compounds gave positive results in a brine shrimp toxicity assay.

Sphingophosphonolipids, phospholipids, and fatty acids from Aegean jellyfish Aurelia aurita

The goal of this study is to elucidate and identify several sphingophosphonolipids from Aurelia aurita, an abundant but harmless Aegean jellyfish, in which they have not previously been described. Total lipids of A. aurita were 0.031-0.036% of fresh tissue, and the lipid phosphorus content was 1.3-1.7% of total lipids. Phosphonolipids were 21.7% of phospholipids and consisted of a major ceramide aminoethylphosphonate (CAEP-I; 18.3%), as well as three minor CAEP (II, III, IV) methyl analogs at 1.3, 1.1, and 1.0%, respectively. The remaining phospholipid composition was: phosphatidylcholine, 44.5%, including 36.2% glycerylethers; phosphatidylethanolamine, 18.6%, including 4.5% glycerylethers; cardiolipin, 5.6%; phosphatidylinositol, 2.6%; and lysophosphatidylcholine, 5.0%. In CAEP-I, saturated fatty acids of 14-18 carbon chain length were 70.8% and were combined with 57.3% dihydroxy bases and 23.4% trihydroxy bases. The suite of the three minor CAEP methyl analogs were of the same lipid class based on the head group, but they separated into three different components because of their polarity as follows: CAEP-II and CAEP-III differentiation from the major CAEP-I was mainly due to the increased fatty acid unsaturation and not to a different long-chain base, but the CAEP-IV differentiation from CAEP-I, apart from fatty acid unsaturation, was due to the increased content of hydroxyl groups originated from both hydroxy fatty acids and trihydroxy long-chain bases. Saturated fatty acids were predominant in total (76.7%), polar (83.0%), and neutral lipids (67.6%) of A. aurita. The major phospholipid components of A. aurita were comparable to those previously found in a related organism (Pelagia noctiluca), which can injure humans.

Lipids of gelatinous Antarctic zooplankton: Cnidaria and Ctenophora

Cnidaria (Calycopsis borchgrevinki, Diphyes antarctica, Stygiomedusa gigantea, Atolla wyvillei, Dimophyes arctica) and Ctenophora (Beroe cucumis, B. forskalii, Pleurobrachia pileus, Bolinopsis infundibulum) were collected near Elephant Island, South Shetland Islands, during January and February 1997 and 1998. Total lipid was low in all zooplankton (0.1-5 mg g wet mass) and included primarily polar lipids (59-96% of total lipid). Triacylglycerols were 0-26% of total lipids, and wax esters were 0-11% in all species. Cholesterol was the major sterol in all Cnidaria (50-63% of total sterols) whereas in most ctenophores it was lower at 26-45%. These cholesterol levels are consistent with a combined carnivorous and phytoplanktivorous diet in the ctenophores, with the carnivorous diet more dominant in the Cnidaria. Other sterols included primarily trans-dehydrocholesterol, desmosterol, 24-methylcholest-5,22E-dien-3beta-ol, 24-nordehydrocholesterol, and 24-methylenecholesterol. Total stanols were 0-6% in all zooplankton. Eicosapentaenoic acid and docosahexaenoic acid were the major polyunsaturated fatty acids (PUFA) in all samples (7-25% of total fatty acids) except for A. wyvillei in which docosapentaenoic acid was 10% of total fatty acids. The PUFA 18:5n-3 was not detected in 1997 samples, but constituted 0.2-0.8% in most 1998 samples. Monounsaturated fatty acids included primarily 18:1n-9c, 16:1n-7c, and 18:1n-7c. The principal saturated fatty acids in all samples were 16:0, 18:0, and 14:0. These data are the first for many of these zooplankton species and the first sterol data for most species. The use of the signature lipid approach has enabled examination of aspects of trophodynamics not obtainable by conventional techniques.

The membrane lipids of the marine ciliated protozoan Parauronema acutum

The membrane lipid composition of the marine ciliated protozoan Parauronema acutum was characterized. Phospholipids of P. acutum comprised 75% of the total lipids and consisted of phosphatidyl ethanolamine (33%), phosphatidyl choline and its phosphono analog (24%), phosphatidyl inositol (12%), phosphatidyl serine (8%), an unidentified phosphonolipid (18%) and small amounts of sphingomyelin, phosphatidic acid and lysophospholipid. Neutral sphingolipids comprised 15% of the total ciliate lipids and consisted of two major glycosphingolipids and six minor glycosphingolipids. These contained two kinds of long chain bases, one of which was sphingosine and either glucose or galactose or mixtures of both. The fatty acids of the total lipids of P. acutum consisted primarily of palmitic acid (13%), oleic acid (6%), linoleic acid (25%), alpha-linolenic aid (12%) plus highly unsaturated fatty acids of the omega - 3 family including all-cis 6,9,12,15-octatetraenoic acid (9%), all-cis 5,8,11,14,17-eicosapentaenoic acid (10%) and all-cis 4,7,10,13,16,19,22-docosa-hexaenoic acid (5%). Individual lipids had their own specific fatty acid patterns.

Phospholipid fatty acid composition of gorgonians of the genus Pseudopterogorgia: identification of tetracosapolyenoic acids

The phospholipid fatty acid composition of the Caribbean gorgonians Pseudopterogorgia acerosa (Pallas), Pseudopterogorgia americana (Gmelin), Pseudopterogorgia bipinnata (Verrill) and Pseudopterogorgia rigida (Bielschowsky) is described for the first time. The main phospholipids identified were phosphatidylethanolamine, phosphatidylcholine and phosphatidylserine. All four gorgonians presented a similar phospholipid fatty acid composition. The main fatty acids were 16:0, 18:3(n-6), 18:4(n-3), 20:4(n-6), 22:6(n-3), 24:5(n-6) and 24:6(n-3). In all of the studied Pseudopterogorgia gorgonians, high amounts of the tetracosapolyenoic fatty acids 24:5(n-6) and 24:6(n-3) were identified. In the four gorgonians studied, n-6 polyunsaturated fatty acids predominated. These results suggest that the occurrence of tetracosapolyenoic fatty acids in the Gorgoniidae is more general than previously recognized.

New branched-chain fatty acids from the Senegalese gorgonian Leptogorgia piccola (white and yellow morphs)

Fatty acids from total lipids of the gorgonian Leptogorgia piccola (white and yellow morphs), collected from the same area at two different periods with regard to the average water temperature, were studied. More than fifty fatty acids were identified as methyl esters and N-acyl pyrrolidides by gas chromatography and gas chromatography/mass spectrometry. Three new, branched-chain unsaturated fatty acids were identified in addition to the unusual 7-methyl-6-hexadecenoic acid, namely 10-methyl-6-hexadecenoic, 7,9-dimethyl-6-hexadecenoic, and 10-methyl-6,9-heptadecadienoic acids. Also 6,9-heptadecadienoic acid was identified. The fatty acid patterns of specimens harvested in colder waters were quite different from those harvested in warmer waters in that the former contained high amounts of methylene-interrupted polyunsaturated acids, including tetracosapolyenoic acids, especially 6,9,12,15,18-24:5 (up to 15.8% of the total acid mixture) and 6,9,12,15,18,21-24:6 (up to 5.3%). Arachidonic acid was, nevertheless, a major component in all the fatty acid mixtures studied (13.6-20.5%). Based on gas chromatography/Fourier transform infrared experiments, the double bonds were assigned the (Z) configuration. Several fatty aldehydes and their dimethyl acetals were also detected, of which the most abundant was octadecanal.

Identification, isolation and characterization of tetracosapolyenoic acids in lipids of marine coelenterates

Several tetracosapolyenoic acids (TPA) were detected in lipids of different marine coelenterates. Two of these acids were isolated and their structures were confirmed by chemical and spectral methods as all-cis-6,9,12,15,18-tetracosapentaenoic and all-cis-6,9,12,15,18,21-tetracosahexaenoic acid. Their distribution among lipids of a number of species of different classes of coelenterates from the northern and tropical seas, among neutral and polar lipids of these organisms was investigated. Significant quantities of TPA were found in all of the Octacorallia species studied. In some cases the sum of TPA reaches the level of 20% of total lipid fatty acids. The fatty acid composition of different coelenterates is also discussed.

Identification of the new 18-hexacosenoic acid in the sponge Thalysias juniperina

The phospholipid fatty acids from the sponge Spheciospongia cuspidifera were studied revealing the presence of the rare 10-octadecenoic acid (10-18:1) and a new 2-methoxyhexadecenoic acid. The phospholipid fatty acids from Thalysias juniperina were also studied revealing the presence of the hitherto unreported 18-hexacosenoic acid (18-26:1). These results tend to indicate that the biosynthetic pathway from 10-18:1 to 18-26:1 may be operative in nature. The phospholipid mixture from the sponges was also analyzed by 31P-NMR and shown to mainly consist of phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, and phosphatidylglycerol. Phosphatidylcholine was not found in the sponges analyzed in this work.

Lipid phase transitions in membranes involving intrinsic periodic curvature

A conformation of the lipid bilayer of membranes is proposed, with periodic curvature corresponding to the minimal surface structure of cubic lipid phases. Evidence is given indicating that activities of lipid synthesis/modification enzymes embedded in the membrane are controlled by the lateral "packing-pressure", so that the lipid bilayer is close to a transition from the lamellar (L alpha) type of conformation to this periodically curved conformation. Such a phase transition mechanism is assumed to be involved in numerous cooperative membrane functions.

Phospholipid studies of marine organisms: 14. Ether lipids of the sponge Tethya aurantia

The novel unesterified alkyl glycerol monoethers, (2S)-1-(hexadecyloxy)-2,3-propanediol (1), (2S)-1-(16-methylheptadecyloxy)-2,3-propanediol (2) and (2S)-1-(15-methylheptadecyloxy)-2,3-propanediol (3) were isolated from the marine sponge Tethya aurantia and were characterized by spectroscopic methods. These three saturated ethers as well as a series of alk-1'-enyl glycerol monoethers were also encountered in the phospholipids of the same sponge after reduction with LiAlH4. Incorporation experiments with dissociated cells of T. aurantia indicated that [1-14C]-hexadecanol was incorporated into the unesterified alkyl glycerol monoethers.