EXTRACELLULAR POLYSACCHARIDES FROM ANKISTRODESMUS DENSUS (CHLOROPHYCEAE)

The dissolved extracellular compounds produced by the Chlorococcalean Ankistrodesmus densus Kors. were investigated for their molecular masses and chemical composition. Gel permeation chromatography showed apparent relative molecular masses of 2 × 106 and 104, respectively, for two distinct fractions, termed A and B. The higher molecular weight fraction (A) contained mainly fucose and 3-O-methylgalactose, whereas galactose, glucose, mannose, and rhamnose were present in smaller amounts. Methylation analyses showed that the main structural features are fucose as a highly branched part of polymer A with substitutions in both position 2 and position 4, the substitutions on one of those positions being primarily terminal 3-O-methylgalactose and the other one involved as the linkage of the main chain of the polymer. Because of the presence of both fucose and 3-O-methylgalactose, this polymer is highly hydrophobic. In fraction B, mannose represented more than 60% of the carbohydrate material present, whereas the remaining part contained rhamnose, fucose, xylose, and glucose in almost equal amounts. 3-O-methylgalactose and galactose were present as minor elements. Fraction B is basically a mannose-containing polymer in which the mannose units are either 14 or 12 linked. Traces of glucuronic acid and protein were present in both fractions; neither sulfate nor phosphate was detected.