Studies on polysaccharides from Angelica acutiloba--IV. Characterization of an anti-complementary arabinogalactan from the roots of Angelica acutiloba Kitagawa.

An anti-complementary polysaccharide, AR-arabinogalactan, was isolated from the roots of Angelica acutiloba Kitagawa (Japanese name = Yamato-Tohki), and purified by chromatography on DEAE-Sephadex A-50, Sephadex G-100, Sepharose CL-2B and concanavalin A-Sepharose. AR-arabinogalactan was composed of arabinose and galactose in a molar ratio of 1.2:1.0 and a small amount of galacturonic acid. The results of methylation and exo-alpha-L-arabinofuranosidase treatment showed that the polysaccharide was a branched arabinogalactan containing a backbone involving galactopyranosyl (1----6) linkages. Most of the arabinose was present as an alpha-L-furanosyl residue in the non-reducing terminals and side chains. The (1----3)-linked galactopyranosyl residue might be linked to the arabinosyl side chains. alpha-L-arabinofuranosidase digestion did not destroy the anti-complementary activity of the polysaccharide. After incubation of the serum with AR-arabinogalactan in the absence of Ca2+ ions, a cleavage of C3 in the serum was detected by immunoelectrophoresis as well as from the consumption of complement when rabbit erythrocytes were used in the assay system. A marked consumption of C4 was also observed to have occurred when serum was incubated with AR-arabinogalactan in the presence of Ca2+ ions. Collectively considered these results indicate that the mode of complement activation by AR-arabinogalactan is via both the alternative and the classical pathway.