Pavão M S, Albano R M, Lawson A M, Mourão P A
Departamento de Bioquímica, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Brazil.
J Biol Chem. 1989 Jun 15;264(17):9972-9.
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 alpha-L-galactopyranose residues sulfated at position 3 and linked glycosidically through position 1----4 are present in F-1 from all three ascidians. However, alpha-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 plicata and A. nigra, but comprise only a minor fraction of F-1 from Clavelina sp. The combination of these various component units gives a complex structure for F-1 from S. plicata and A. nigra, whereas F-1 from Clavelina sp. 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 Clavelina sp), 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.
海鞘被囊中存在的硫酸化多糖在分子量和化学组成上有显著差异。所有物种中都存在一种高分子量组分（F-1），其半乳糖含量高且具有强烈的负旋光性。对三种海鞘详细研究后发现，其F-1组分存在一些结构差异。所有三种海鞘的F-1中都存在大量在3位硫酸化且通过1→4糖苷键连接的α-L-吡喃半乳糖残基。然而，在黑瘤海鞘的F-1中心核心中，1→3连接且在4位部分硫酸化的α-L-吡喃半乳糖单元约占糖单元的一半。此外，皱瘤海鞘和黑瘤海鞘的F-1中存在L-吡喃半乳糖非还原端单元，但在棒海鞘的F-1中仅占一小部分。这些不同组成单元的组合使得皱瘤海鞘和黑瘤海鞘的F-1具有复杂结构，而棒海鞘的F-1结构更简单。这些海鞘聚糖的结构在所有先前描述的硫酸化多糖中是独特的，因为它们高度分支（棒海鞘除外），在3位硫酸化，并且含有大量L-半乳糖而没有其D-对映体。这些数据展示了动物组织中具有结构功能的聚阴离子聚糖的不寻常例子。
