Effect of exo-beta-D-(1->3)-galactanase digestion on complement activating activity of neutral arabinogalactan unit in a pectic arabinogalactan from roots of Angelica acutiloba Kitagawa

A complement activating pectic arabinogalactan (AGIIb-1) has been isolated from roots of Angelica acutiloba Kitagawa, and a neutral arabinogalactan (N-I) unit, which was liberated from a side chain in AGIIb-1 by mild acid hydrolysis, has found to show the most potent complement activating activity among the arabinogalactan side chains of AGIIb-1. In order to clarify the essential carbohydrate side chains in N-I for the activity, neutral arabinogalactan (AF-N-I) unit, which was obtained from exo-alpha-L-arabinofuranosidase-digested AGIIb-1, was digested with exo-beta-D-(1-->3)-galactanase from Irpex lacteus. The galactanase digestion of the AF-N-I unit completely stopped its reactivity with beta-D-glucosyl-Yariv antigen, and significantly reduced its complement activating activity. The digestion products gave high molecular weight fragments (GN-1A and -1B) and intermediate size fragments in addition to beta-D-(1-->6)-galactosyl mono to pentasaccharides as the side chains of the AF-N-I unit. Among the fragments, GN-IA, GN-1B and intermediate size fragments showed relatively potent complement activating activity, suggesting that these side chains in the N-I unit might be responsible for expression of the activity of the N-I unit. (C) 1997 Elsevier Science Ltd.