Relationship between structure and activity of an anti-complementary arabinogalactan from the roots of Angelica acutiloba Kitagawa.

An anti-complementary arabinogalactan (AGIIb-1), isolated from the roots of Angelica acutiloba Kitagawa, comprised one neutral (N-I) and two acidic arabinogalactan (A-I and A-II) units and one neutral arabinan unit (N-II). N-I showed the most potent anti-complementary activity. AGIIb-1, A-I, and A-II had similar moderate activities, but N-II had weak activity. The product (AF-AGIIb-1) of digestion of AGIIb-1 with exo-alpha-L-arabinofuranosidase had markedly increased anti-complementary activity, as did that (AF-N-I) of N-I. Degradation of the rhamnogalacturonan core in AGIIb-1 slightly decreased the anti-complementary activity, whereas the high-molecular-weight neutral arabinogalactan and galacto-oligosaccharide side-chains in A-I and A-II showed potent activities. When AF-AGIIb-1 was digested with endo-arabinanase, the activity decreased slightly. Partial elimination of the (1--6)-beta-D-galactosyl side-chains from AF-N-I by digestion with exo-beta-D-galactosidase did not affect the activity. AGIIb-1 reacted weakly with the beta-D-glucosyl-Yariv antigen, but AF-AGIIb-1 and AF-N-1 had increased reactivity with the antigen. The anti-complementary activity of AGIIb-1 was expressed mainly through the classical pathway, whereas AF-AGIIb-1 and AF-N-I had markedly increased activity through the alterative pathway.