Studies on the Enzyme Immunoassay of Bio-active Constituents in Oriental Medicinal Drugs. VI. Enzyme Immunoassay of Ginsenoside Rb_1 from Panax ginseng

Enzyme immunoassay (EIA) of ginsenoside Rb_1 (GRb_1), one of the glucosides of protopanaxadiol from Panax ginseng, was explored. A carrier protein (bovine serum albumin (BSA)) was coupled to the C-26 position on the unsaturated side chain of the protopanaxadiol moiety to prepare the immunogen. In order to perform bridge heterologous EIA, a label (β-D-galactosidase) was introduced at C-26 of the saturated side chain to obtain labeled antigen. Anti-GRb_1 antisera were elicited in rabbits by immunization with GRb_1-BSA conjugate(9). The double antibody method (with goat anti-rabbit IgG antiserum) was used to separate the bound and free GRb_1-β-Gal. A satisfactory standard curve for EIA of GRb_1 was obtained in the range of 0.04-10ng/tube. In a comparison of the assay results obtained by EIA and HPLC, the linear regression equation and correlation coefficient for the two methods were y(EIA)=9.18x(HPLC)-0.033 and 0.98,respectively. The anti-GRb_1 antiserum cross-reacted with GRb_2 (21.8%) and GRc (10.6%), which are also constituents of Panax ginseng.