Structure of an anti-complementary arabinogalactan from the root of Angelica acutiloba Kitagawa.


Kiyohara H, Yamada H




Carbohydr Res


Mild acid hydrolysis of an anti-complementary arabinogalactan (AGIIb- 1), isolated from the roots of Angelica acutiloba Kitagawa, gave one neutral (N-I) and two acidic arabinogalactan (A-I and A-II) units and one neutral arabinan unit (N-II). The methyl-esterified rhamnogalacturonan cores of A-I and A-II were subjected to base- catalysed beta-elimination in the presence of sodium borodeuteride to give the neutral side-chains. Gel filtration showed that A-I contained a high-molecular-weight arabinogalactan and two oligosaccharides consisting of Ara and Gal or Ara as the side chains, and that A-II was composed of two high-molecular-weight arabinogalactans. Similar treatment of the acidic fraction, obtained by partial acid hydrolysis of A-I, gave mono- to tetra- galactosylgalactitol-1-d. Partial acid hydrolysis showed that the rhamnogalacturonan core of A-I contained the sequences --4)-GalA-(1-- 2)-Rha-(1-- and --4)-GalA-(1--4)-Rha-(1--. Digestion with exo-beta-D- galactosidase and Smith degradation indicated that N-I contained a (1- -3)-linked galactan backbone with 6-inked galactosyl side-chains. The galactan components of A-I and A-II contained chains that were rich in 3-linked Gal. Fluorescent-labelling with 2-aminopyridine indicated that Ara was the reducing terminal in N-II, whereas it was Rha in A-I and A-II. The mild acid treatment of a different AGIIb-1 preparation gave an oligosaccharide fraction which consisted mainly of terminal and 3-linked Arap, 4- or 5-linked Ara, terminal, 4-linked, and 4,6- linked Gal, and terminal GlcA, and contained Gal and Rha as the reducing terminals.