Structural characterisation of an anti-complementary pectic polysaccharide from the roots of Bupleurum falcatum L.

An anti-complementary pectic polysaccharide (BR-2-IIb), isolated from the roots of Bupleurum falcatum L., has an average molecular weight of 36,000 (gel filtration), and was subjected to methylation analysis before and after carboxyl-reduction, digestion with endo-polygalacturonase, base-catalysed β-elimination, and partial acid hydrolysis. BR-2-IIb consisted mainly of galacturonic acid, arabinose, rhamnose, and galactose in the molar ratios 13.0:2.1:1.4:1.0 and contained a large enzyme-sensitive polygalacturonan region. The enzyme-resistant region (PG-1) was rich in neutral sugars and contained a backbone of 4-linked GalA and 2-linked Rha to which a highly branched arabinogalactan was attached to position 4 of some 2-linked Rha units. Partial acid hydrolysis of BR-2-IIb gave Ara-(1→3)-Ara, Ara-(1→4)-Arap, Ara-(1→5)-Araf, Ara-(1→6)-Gal, Gal-(1→4)-Gal, GalA-(1→2)-Rha, GalA-(1→4)-Rha, GalA→Rha→Rha, Gal→Rha→Rha, and GalA-(1→6)-Gal in addition to (1→4)linked oligogalacturonides. The anti-complementary activity of BR-2-IIb was enhanced by de-esterification, but carboxyl-reduction decreased the activity.