| Abstrakt: |
The sulfated polysaccharides that occur in the tunic of ascidians differ markedly in molecular weight and chemical composition. A high molecular weight fraction (F-1), which has a high galactose content and a strong negative optical rotation, is present in all species. Several structural differences were observed among the F-1 fractions obtained from three species of ascidians that were studied in detail. Large numbers of α-L-galactopyranose residues sulfated at position 3 and linked glycosidically through position 1→4 are present in F-1 from all three ascidians. However, α-L-galactopyranose units, 1→3-linked and partially sulfated at position 4, comprise about half of the sugar units in the central core of F-1 from Ascidian nigra. In addition, L-galactopyranose nonreducing end units occur in F-1 from Styela plicataand A. nigra, but comprise only a minor fraction of F-1 from Clavelinasp. The combination of these various component units gives a complex structure for F-1 from S. plicataand A. nigra, whereas F-1 from Clavelinasp. possesses a simpler structure. The structures of these ascidian glycans are unique among all previously described sulfated polysaccharides, since they are highly branched (except that from Clavelinasp), sulfated at position 3, and contain large amounts of L-galactose without its D-enantiomorph. These data show unusual examples of polyanionic glycans with structural function in animal tissues. |
