Structural studies on ascophyllan and the fucose-containing complexes from the brown alga Ascophyllum nodosum

The two major “complexes” isolated from a dilute-acid extract of Ascophyllum nodosum were degraded by mild, acid hydrolysis to a fucan portion and an ascophyllan-like portion. Protein was enriched in the ascophyllan-like fraction. A time-course study of the acid hydrolysis, together with data on digestion by pronase and hydrolysis by base indicated that the complexes were formed by a fucan backbone to which varyious numbers of ascophyllan-like molecules were attached by an acid-labile linkage. The primary uronic acid in the ascophyllan-like portion of the complex was mannuronic acid, whereas the free ascophyllan isolated in this study contained a mixture of guluronic, mannuronic, and glucuronic acids*. In each of these uronic acid-rich materials, hydrolysis by base suggested a uronic acid backbone having relatively long, fucose-containing, side chains. Hydroxyproline was present in the complex, but did not appear to be part of the major carbohydrate-protein linkages. A protein-enriched fraction was obtained by treatment of the ascophyllan-like portion of the complex with oxalic acid. Amino acid analysis, before and after treatment with mild base suggested that serine and threonine were involved in the linkage of protein to carbohydrate.