Complement activating galactan chains in a pectic arabinogalactan (AGIIb-1) from the roots of Angelica acutiloba Kitagawa

The complement activating (anti-complementary) arabinogalactan (AGIIb-1), isolated from the roots of Angelica acutiloba Kitagawa, was digested with exo-beta-D(1-->3)-galactanase after a preceding digestion with exo-alpha-L-arabinofuranosidase. Gel filtration of the digested products gave a high molecular weight fraction (HMW) which could not be further digested, and an oligosaccharide fraction (LMW). The latter originated from exterior beta-D-(1-->3)-galactan chains of AGIIb-1. HMW showed similar potent anti-complementary activity as arabinofuranosidase-digested AGIIb-1 (AF-AGIIb-1), but LMW did not show any activity. HMW was composed mainly of Ara and Gal in addition to small proportions of Rha, Xyl, GlcA and GalA. Methylation analysis indicated that HMW comprised terminal Araf, terminal Gal and 3,6-linked Gal as well as 4-linked Gal, Clinked GalA and terminal GlcA. Further digestion of HMW with endo-beta-D-(1-->4)galactanase gave a polymeric fraction (GN-1) and oligosaccharidefraction (GN-2). Although most of beta-D-(1-->4)-galactosyl chains were liberated from HMW by this galactanase digestion, anti-complementary activity of GN-1 was not changed significantly in comparison with that of HMW. Controlled Smith degradation of HMW gave four kinds of fractions. Among them, the fraction (CSD-1) having the largest molecular-weight showed a relatively potent anti-complementary activity, and it was mainly composed of a (1-->3)-galactan. Exo-beta-D-(1-->3)-galactanase digestion of CSD-1 gave six fractions (CSD-1-1 similar to CSD-1-6). The polymeric fraction (CSD-1-1) and the oligosaccharide fractions (CSD-1-4 and 1-5) had potent anti-complementary activity. Methylation analysis indicated that CSD-1-1, 1-4 and 1-5 consisted mainly of terminal, 6-linked and 3,6-linked Gal. CSD-1-4 and CSD-1-5 were also mainly composed of 3-linked Gal. These results indicates that complement activating ability of AGIIb-1 is expressed by the inner galactan chains. Copyright (C) 1996 Elsevier Science Ltd.