Studies on the Enzyme Immunoassay of Bio-active Constituents Contained in Oriental Medicinal Drugs.IV. : Enzyme Immunoassay of Glycyrrhetic Acid

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Enzyme immunoassay of glycyrrhetic acid was developed by employing antisera elicited from in rabbits immunized with C-3 bridged glycyrrhetic acid-bovine serum albumin (BSA) conjugate (15, 16) and C-3 bridged glycyrrhetic acid-β-galactosidase conjugate (17, 18) as labeled antigens. Hemisuccinyl and hemiglutaryl groups, which were chosen as the chemical bridges, were introduced at the hydroxy group of tert-butyl glycyrrhetate (2). Immunoassay was performed with bridge heterologous combinations such as anti-glycyrrhetic acid-hemisuccinate-BSA (15) antiserum and glycyrrhetic acid-hemiglutarate-β-galactosidase conjugate (18) and the reverse combination (16 and 17). The sensitivity of enzyme immunoassays (EIA) expressed as the midpoint (logit B/B₀=0) was higher in the former combination (2.4 ng/tube) than the reverse combination (8.6 ng/tube). The cross reactivities of the anti-C-3 bridged glycyrrhetic acid antisera with C-3 substituted derivatives of glycyrrhetic acid were higher than those of the anti-C-30 bridged glycyrrhetic acid antiserum.