In this paper, an acidic polysaccharide HDP3A was isolated from Hovenia dulcis peduncles with 45.9% of uronic acid content. Structure of HDP3A was elucidated by chemical and spectroscopic analysis. HDP3A was mainly contained of galacturonic acid, galactose, rhamnose and arabinose with a small quantity of xylose, fucose, mannose, glucose. The structural analysis indicated that HDP3A was a pectin-type polysaccharide with HG and RG-I regions and hairy regions. HG was linear homopolymer with repeating units of (1→4)-α-d-galactopyranosyl uronic (GalA) residues. The GalpA residues in HG domain may be acetylated and/or methyl-esterified. The backbone of RG-I contains repeating units of [→α-GalpA-1,2)-α-Rhap-1,4→]n and the hairy regions attached in the Rha at position O-4. Hairy regions were mainly composed of galactans, arabinans, arabinogalactans, glucans, mannans and xylans. The immunomodulatory activities of HDP3A and its reduced (HDP3A-R) and hydrolyzed product (HDP3A-0.1) in vitro on macrophages were determined. The three polysaccharide fractions all stimulated the proliferation of RAW264.7 cells and the order of the proliferative effects was HDP3A>HDP3A-R>HDP3A-0.1, indicating that the immune effects of pectin-type polysaccharides were related to branches and molecular weight. Consequently, HDP3A could be as a potential source for the proliferative activity.
Keywords: HG; Hovenia dulcis; Immunomodulatory activities; Linkage analysis; RG-I; Structural elucidation.
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