A heterologous enzyme immunoassay of prostaglandin E2 using a stable enzyme-labeled hapten mimic

A sensitive heterologous enzyme immunoassay for prostaglandin E2 was developed using 9-deoxy-9-methylene-prostaglandin F2 alpha as a stable prostaglandin E2 mimic. beta-Galactosidase was conjugated to the hapten mimic. Anti-prostaglandin E2 IgG was bound to a polystyrene tube. The enzyme-labeled hapten mimic mixed with unlabeled prostaglandin E2 was allowed to react in a competitive manner with the immobilized antibody. Then, the beta-galactosidase specifically bound to the antibody was assayed fluorometrically, and the enzyme activity was correlated with the amount of unlabeled prostaglandin E2. According to the calibration curve thus obtained, prostaglandin E2 could be determined in a range of 1.2-430 fmol. Prostaglandin E2 was extracted from human urine by the use of an octadecylsilyl silica column. The crude extract contained a substance(s) which disturbed the enzyme immunoassay and gave an apparently high content of prostaglandin E2. The interfering substance was separated from prostaglandin E2 by reverse-phase high-performance liquid chromatography. The purified urinary extract was examined by the enzyme immunoassay for prostaglandin E2, and the validity of the results was confirmed by gas chromatography-selected ion monitoring.