Sialoglycolipids

In the sixties, however, sialoglycolipids were found in the tissues of some invertebrates, the sea urchins Arbacia punctuata,64 Pseudocentrotus depressus,6S and Strongylocentrotus intermedius.66 These compounds were soon found in other species belonging to the phylum Echinodermata, and their systematic study began. 

The authors assumed that this glycolipid creates ionogenic centers in cellular membranes, similar to those that appear because of the presence of a sialic acid in sialoglycolipids.262... 

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... 

Later, from the eggs of S. intermedins, two sialoglycolipids were isolated that had the same type of structure as the sialoglycolipid from the gonads, but they contained only N-glycolylneuraminic acid, and, in one of them, this acid was sulfated.289,290... 

In the spermatozoa of the sea urchin Anthocidaris crassipina, nine sialoglycolipids were found, two of which were isolated and their structures established from the results of acid hydrolysis, methylation, and periodate oxidation.139 The major component of the glycolipid mixture is a disialo-glycolipid, NeuAc-(2- 8)-NeuAc-(2- 6)-Glc-Cer. The least-polar, minor component has the structure of a monosialoglycolipid, NeuAc-(2 - 6)-Glc-Cer. In these compounds, glucose is again the only neutral monosaccharide, and the sialic acid is attached to it at 0-6. 

From the S. nudus gonads, mono- and di-sialoglycolipids were isolated as well.291 Their structures are similar to those of the sialoglycolipids from A. crassipina. 

The second major sialoglycolipid from E. cordatum was the most acidic. Its carbohydrate chain contained one sialic acid residue and one glucosyl residue, as well as a sulfate group at C-8 of the sialic acid.141 This was the first example found in Nature of a sialoglycolipid containing a sulfated sialic acid. The structure proposed for the glycolipid is as follows. 

Sulfated sialoglycolipids have also been found as the major sialoglycolipid components in the gonads of another sea urchin species, E. parma, belonging... 

The position of the bond between the sialic acids was determined by g.l.c.-m.s. of the acetates of partially methylated sialic acid derivatives obtained after methanolysis of the methylated sialoglycolipid, and was confirmed by the periodate-oxidation data. The (2- 9) bond between... 

Thus, the sialoglycolipids from E. retifera and A. amurensis starfish, which are closely related, contain an amino sugar, absent from the sialoglycolipids of other species of echinoderm, and possess the same trisaccharide chain-structure for the asialo derivative. They differ, however, in the type of sialic acids, and their location in the carbohydrate chain. 

From the whole starfish were isolated three monosialoglycolipids whose carbohydrate chains contain glucose, galactose, arabinose, and N-glycolyl-neuraminic acid. From the results of partial hydrolysis with acid, methanoly-sis, methylation, and Cr03 oxidation, the following structures have been proposed for these sialoglycolipids. 

The more-polar sialoglycolipid is a disialoglycolipid having a linear octasac-charide chain. Both N-acetylneuraminic acid residues are situated inside the chain and glycosylated at 0-4 by galactosyl residues.207... 

The lipid moiety of the sialoglycolipids from the hepatopancreas of P. pectinifera includes a-hydroxy fatty acids, among which, the C22, C23, and C24 acids account for >90% of the mixture, and compounds whose major... 

Therefore, from the starfish P. (A) pectinifera of the order of Spinulosa, unique sialoglycolipids not encountered in other species of animals have been isolated. At present, it is impossible to decide whether this type of structure is characteristic for the sialoglycolipids of starfish belonging to this order for such a decision to be made, it will be necessary to investigate further the other starfish species of Spinulosa. 

As in the case of the gangliosides in vertebrates, the sialoglycolipids in sea urchins are cell-surface antigens. A study of antigenic specificity for two disialoglycolipids (from the eggs of S. intermedius) whose structures differ in only one respect, that a sulfate group is present on the sialic acid... 

Similarly to the gangliosides of higher animals, the sialoglycolipids in sea urchins seem to take part in growth control. For the S. intermedius embryos, the exposure of sialoglycolipids at the cell surface has been shown to depend on the cell density in the incubation medium in sparse embryos, they are much more exposed than in the dense ones.290 This phenomenon seems to be similar to the fact, known for mammalian cells, that the synthesis of glycolipids depends on cell contact.12-13... 

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