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Isolation and Structural Characterisation of Rhamnogalacturonan in Ginseng Roots
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Edité par CCSD -
National audience. Panax ginseng C. A. Meyer (ginseng) has been used as a traditional medicine in Asia for thousand years. As one of the active components in ginseng, polysaccharides have many pharmaceutical activities. Ginseng polysaccharides are composed of neutral glucans and pectin. In this study, ginseng pectin was first de-esterified by alkali, and then hydrolyzed by endo-polygalacturonase. The hydrolysate was fractionated by a combination of anion-exchange and size exclusion chromatography, and four pectic domains (1A, 1B, 2A and 2B) were obtained. IR and NMR spectra indicated that there were nearly no methyl-ester and acetyl groups in these fractions. They were all composed of GalA, Rha, Ara and Gal as the main components. Fractions 1A and 2A were homogeneous and their molecular weights were 8.3×104 and 1.2×105 Da, respectively. The ratios of Rha/GalA were 0.96 and 0.65, for 1A and 2A, respectively, typical of RG-I domains. Both fractions could be hydrolyzed by rhamnogalacturonan hydrolase, which gives further evidence that they are RG-I type pectin. With its Rha/GalA ratio close to 1, fraction 1A is the most purified RG-I domain from ginseng up to now. Fractions 1B and 2B exhibited molecular weights of 6.4×103 and 6.5×103 Da, respectively. Based on a two-step mild acid hydrolysis coupled to the analysis of the resulting fragments by mass spectrometry, they were indentified to be RG-II type pectin. Fragments corresponding to RG-II backbone and side chains A, B and E were distinguished. This is the first time RG-II structures are identified in ginseng roots.
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