Controlled Smith degradation of ukonan C, a phagocytosis-activating polysaccharide isolated from the rhizome of Curcuma longa L., was performed. The reticuloendothelial system-potentiating, anti-complementary and alkaline phosphatase-inducing activities of ukonan C and its degradation products were investigated. Methylation analyses of the primary and secondary Smith degradation products and of a de-arabinoxylated product indicated that structural features of the arabinogalactan core of ukonan C include a backbone chain composed of β-1, 3-linked D-galactose and β-1, 4-linked D-xylose. All of the galactose units in the backbone carry side chains composed of β-1, 6-linked D-galactosyl residues with or without terminal α-L-arabinose units at position 3. Ukonan C showed remarkable effects on both reticuloendothelial system-potentiating and alkaline phosphatase-inducing activities. Periodate oxidation caused a decrease in or disappearance of the immunological activities, but the controlled Smith degradation product having the arabinogalactan core structure of polysaccharide showed a pronounced effect on anti-complementary activity.
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