Difference in structure and complement fixing activity of pectic polysaccharides from different plant parts of Echinacea purpurea (L.) Moench.

Water soluble pectic polysaccharide fractions were isolated from different parts of Echinacea purpurea in order to elucidate any structural and biological differences. Water extracts of stems, leaves, flower buds, open flowerheads, post fertile flowers and roots were purified by ion exchange chromatography and by gelfiltration. The polysaccharides consisted of a high amount of galacturonic acid, but also rhamnose, arabinose and galactose with glycosidic linkages compatible with rhamnogalacturonan type I (RG-I), arabinogalactan I (AG-I) and arabinogalactan II (AG-II) structures. Precipitation with Yariv-reagent supports the presence of AG-II. The polysaccharides isolated from the different plant part showed largely the same structure, but with some differences mainly in the arabinan component. The complement fixing activity varied considerable between the plant parts. The structural elucidation indicated that the glycosidic linkages to arabinose are important for the complement fixating activity, and thus a diminished activity after weak hydrolysis of the pectic fractions was observed.   Key words: Complement fixing activity, Echinacea, glycosidic linkages, pectic polysaccharides, Yariv-reagent.