Pectic polysaccharides from roots of Glycyrrhiza uralensis: Possible contribution of neutral oligosaccharides in the galacturonase-resistant region to anti-complementary and mitogenic activities

Digestion with endo-α-(1 → 4)-polygalacturonase liberated the enzyme-resistant region (PG-1c) as an active site of the anti-complementary and mitogenic pectic polysaccharide (GR-2IIc) from Glycyrrhiza uralensis. Partial acid hydrolysis of PG-1c resulted in acidic oligosaccharides, and methylation analysis and GC-MS analysis of the acidic oligosaccharides suggested that PG-1c comprised a rhamnogalacturonan core. Degradation of uronic acids by lithium decreased the anti-complementary and mitogenic activities of PG-1c. Although the products from PG-1c were still active, the methylglycoside of α-L-Rha-(1 → 4)-α-D-GalA-(1 → 2)-α-L-Rha-(1 → 4)-α-D-GalA did not show both activities. The products obtained by the lithium degradation from PG-1c gave fractions containing various neutral oligosaccharide-alditols. Among these fractions the longest and the short oligosaccharide-alditol fractions had relatively potent anti-complementary activity, whereas all oligosaccharide-alditol fractions expressed weak but significant mitogenic activity. GC-MS analysis indicated that the short oligosaccharide-alditol fraction contained various kinds of di- to tetrasaccharide-alditols. However, malto-oligosaccharide-alditols, and malto-, isomalto-, and laminari-oligosaccharides did not show anti-complementary and/or mitogenic activities, and these results suggested that certain neutral carbohydrate chains in PG-1c were responsible for the expression of mitogenic activity as well as anti-complementary activity of PG-1c.