RHAMNOGALACTURONAN-II DIMERS CROSS-LINKED BY BORATE DIESTERS FROM THELEAVES OF PANAX-GINSENG MEYER,C.A. ARE RESPONSIBLE FOR EXPRESSION OF THEIR IL-6 PRODUCTION ENHANCING ACTIVITIES

Leaves of Panax ginseng C.A. Meyer contain larger amounts of thiobarbi turic acid (TBA)positive material, suggested to be rhamnogalacturonan II (RG-II), than the roots. Starting from leaves, three different poly saccharides, GL-RI, GL-RII and GL-RIII, were isolated from polysacchar ide subfraction GL-5 by subsequent anion-exchange and size-exclusion c hromatography. Sugar and methylation analyses indicated that the three polysaccharides consisted of the same substitution patterns of 2-O-me thyl-fucose, 2-O-methyl-xylose, apiose, 3-C-carboxy-5-deoxy-L-xylose ( aceric acid, AceA), 3-deoxy-D-manno-2-octulosonic acid (Kdo), and 3-de oxy-D-lyxo-2-heptulosaric acid (Dha), being characteristic monosacchar ides of RG-II, but no other pectic components. Another RG-II (GL-4IIb2 ) has also been isolated without endo-polygalacturonase digestion from leaves of P, ginseng, and turned out to be a macrophage Fc receptor e xpression enhancing polysaccharide [K.-S. Shin, II. Kiyohara, T. Matsu moto, and H. Yamada, Carbohydr. Res., 300 (1997) 239-249]. GL-4IIb2 an d GL-RIII had relatively potent interleukin-6 (IL-6) production enhanc ing activity of macrophages, however, GL-RI and GL-RII had negligible and weak enhancing activities, respectively. Partial acid hydrolysis ( 0.1M trifluoroacetic acid, 40 degrees C, 24h) of GL-RI, GL-RII and GL- RIII gave in each case a large-size fraction (AH-I), an intermediate-s ize fraction (AH-2) and a short oligosaccharide fraction (AH-3). EIMS and FARMS analyses indicated that AH-3 consisted of Rha-(1-->5)-Kdo an d Ara-(1-->5)-Dha, and that AH-2 comprised non-, mono- and di-acetylat ed AceA-containing hexa- to nona-saccharides. Also for AH-1 no signifi cant structural differences were observed among the polysaccharides, b ut the presence of microheterogeneity is suggested. The AH-1 fractions did not show any IL-6 production enhancing activity. Size-exclusion H PLC indicated that GL-RIII mainly comprised RG-II of higher molecular mass (12,000), and that GL-RI and GL-RII mainly contained RG-II of low er molecular mass (7000). Boron content and B-11 NMR analyses indicate d that the higher molecular weight polysaccharide in GL-RIII was mainl y present as a RG-II dimer cross-linked by berate diesters.