Glycolipids occurrence

Pseudo-glycolipids. The interest for glycolipids is connected with their occurrence in biological systems, as well as their physicochemical properties, the two viewpoints being sometimes correlated. For example in membranes, lipid rafts are sub-domains which contain liquid-ordered phases.73... 

The mesogenic structures of glycolipids are due to the occurrence, on the same molecule, of a hydrophilic and a hydrophobic moiety often referred to as head and tail respectively. As a result, glycolipids are able to self-organize into a large variety of mesophases also called liquid crystals (Fig. 2) [ 10]. Supramolecular assemblies of mesogenic compounds can be caused by a rise in temperature (thermotropic liquid crystals) or by the addition of water (lyotropic liquid crystals) they result from different responses of the carbohydrate and the alkyl chain to temperature or solvent (water), respectively. 

The occurrence of 3-deoxy-D-manno-octulosonic acid in lipopoly-saccharides has prompted its synthesis,537 together with the D-gal-octo158 and the D-gluco analogs.157 Although gas-liquid chromatography was successfully used to analyze the products of these syntheses, it has been reported that methanolysis of a bacterial endotoxin lipopolysaccharide failed to yield 3-deoxy-D-manno-octulosonic acid, presumably because of the lability of the latter to acid.381 However, Kasai and Nowotny have reported four peaks for the O-trimethylsilyl derivatives of 3-deoxy-D-manno-octulosonic acid obtained by methanolysis of the glycolipid from a Salmonella minnesota mutant.538 Reduced 3-deoxy-D-manno-octulosonic acid and its methyl ester have also been analyzed successfully as their acetates.339,539... 

Echinoderms constitute a peculiar phylum of invertebrates belonging to the most highly organized animals, the Deuterostomia, including, also, all the phyla of chordates. Among the invertebrates, echinoderms are the richest in glycolipids, and differ from all of the other marine invertebrate phyla in that they contain sialoglycolipids.79 This conforms to the data of Warren, who studied the occurrence of sialic acids in Nature, and found that all of the vertebrates have them, but, of the invertebrates, only the echinoderms practically all of the Protostomia contain no sialic acids.274... 

The major purpose of the present study was to describe, and to quantify, the widespread occurrence of natural complement-fixing autoantibodies against numerous simple glycolipids. We show that every individual rabbit and human serum tested had complement-fixing autoantibodies against glycolipids that are widely distributed in circulating blood cells and other tissues. 

Numerous studies of specificities of anti-glycolipid antibodies produced by immunizing rabbits have been reported (8,9), and some discrepancies have been noted between laboratories (9). The widespread occurrence of natural antibodies might cause confusion in analyzing specificities produced by experimental immunization. Because of this we have purified both immune and natural anti-glycolipid antibodies from rabbit sera, and we have compared their specifities against the same, and different, glycolipids. 

Acylneuraminic acids have been found so far only in mammalians and in some bacteria, but never in plants. They are widespread occurrence as components of glycoproteins and glycolipids both in invertebrates and in vertebrates, in cells and in body fluids [4]. 

This chapter focuses on the occurrence and the physicochemical properties of glycolipids in Nature. Owing to space limitations, the presented overview must be incomplete, and, thus, mainly publications of the past 15 years are included. However, all review articles cited herein inform the interested reader about earlier work. Although lipopolysaccharides (LPS), lipoara-binomannan (LAM), lipomannan, lipoglycans, and lipoteichoic acids are not understood as glycolipids per definition, their occurrence and properties are also described in this chapter. GPI-anchored lipids is a main topic ofO Chap. 7.4. 

Occurrence. D-Lyxose (7), a rare sugar, has been detected in glycolipids from Mycobacterium phlei. The pentose is substituted by an acyl group at position 2 and in some instances, at both positions 2 and 4. It is difficult to distinguish d-lyxose from D-arabinose, and thus, a wider distribution in Mycobaterium should be... 

Plant lipids are of two main types structural and storage. The structiu lipids are present as constituents of various membranes and protective surface layers and make up about 7 per cent of the leaves of higher plants. The surface lipids are mainly waxes, with relatively minor contributions from long-chain hydrocarbons, fatty acids and cutin. The membrane lipids, present in mitochondria, the endoplasmic reticulmn and the plasma membranes, are mainly glycolipids (40-50 per cent) and phosphoglyc-erides. Plant storage lipids occur in fruits and seeds and are, predominantly, triacyl-glycerols. Over 300 different fatty acids have been isolated from plant tissues, but only about seven are of common occurrence. The most abundant is a-linolenic acid the most common saturated acid is palmitic acid and the most common monounsaturated acid is oleic acid. 

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