THE CELL-WALL (THECA) OF TETRASELMIS-STRIATA (CHLOROPHYTA) - MACROMOLECULAR-COMPOSITION AND STRUCTURAL ELEMENTS OF THE COMPLEX POLYSACCHARIDES

Isolated cell walls (thecae) from the scaly flagellate green alga Tetr aselmis striata Butcher contain the unusual 2-keto-sugar acids 3-deoxy -manno-2-octulosonic acid (Kdo), 3-deoxy-5-O-methyl-manno-2-octulosoni c acid (5OMeKdo), and 3-deoxy-lyxo-2-heptulosaric acid (Dha). In addit ion, galacturonic acid, galactose, gulose, and arabinose are present. EDTA-extraction yielded an insoluble fraction that retains the shape o f the cell walls and contains no 2-keto-sugar acids. Methylation analy sis demonstrated the presence of terminal hexose, GalA, Dha, and Kdo a s well as 2-substituted hexose, 4- or 8-substituted Kdo, and 4,8-di-su bstituted Kdo. However, most of the carbohydrate material (about 60%) was not methylated. Periodate oxidation of the cell wall preparation s howed the presence of 2-substituted Gul, 4- or/and 5-substituted and 7 - or/and 8-substituted Kdo, which is in agreement with the methylation analysis. Again, a significant amount of carbohydrate material was no t degraded, indicating complex substitution patterns. Oligosaccharides were generated by partial hydrolysis and fractionated using gel perme ation chromatography and high-pH anion-exchange chromatography. Oligos accharides contained either GalA and Kdo, or Gal, Kdo, Dha, and Gal, r espectively. The structure of a GalA and Kdo containing disaccharide w as established using H-1 NMR spectroscopy.