Rhamnogalacturonan I domains from ginseng pectin

Five rhamnogalacturonan I (RG-I) domains RG-I-1, RG-I-2, RG-I-3A, RG-I-3B and RG-I-4 were isolated from ginseng pectin by endo-polygalacturonase hydrolysis and a combination of ion-exchange and gel-permeation chromatography. The five domains all contain galacturonic acid, rhamnose, galactose and arabinose as main components and their rhamnose/galacturonic acid is from 0.26 to 0.64, among the range of RG-I. The molecular weights of RG-I-1 (5 kDa), RG-I-2 (4 kDa) and RG-I-3B (6 kDa) are smaller than those of RG-I-3A (45 kDa) and RG-I-4 (60 kDa). 13C NMR spectra of all domains showed RG-I features. RG-I-2 and RG-I-3B contained RG-I domains linked with highly methyl-esterified and acetylated homogalacturonan domains and the side chains probably belonging to type I and type II arabinogalactans, while RG-I-3A and RG-I-4 may have the side chains of type I arabinogalactans. 4-O-methyl-β-d-glucuronic acid residues were present at non-reducing terminals of RG-I-2.