Enzyme immunoassay of 6-ketoprostaglandin F1 alpha in a solid phase.

A solid-phase enzyme immunoassay of 6-ketoprostaglandin F1 alpha (a stable degradation product of prostaglandin I2) was developed in which the hapten molecule was labeled with beta-galactosidase. The antiserum was bound to a polystyrene tube, and the enzyme-labeled and unlabeled 6-ketoprostaglandin F1 alpha were allowed to react in a competitive manner with the immobilized antibody. The activity of the immunologically bound beta-galactosidase was assayed by fluorometry, and correlated with the amount of unlabeled 6-ketoprostaglandin F1 alpha. According to a calibration curve 6-ketoprostaglandin F1 alpha was detectable in a range of 30 fmol-10 pmol. When 6-ketoprostaglandin F1 alpha was extracted from human serum by using an octadecylsilyl silica column (Sep-Pak C18) and the crude extract was subjected to the enzyme immunoassay, the content of 6-ketoprostaglandin F1 alpha was 50-60 pmol/ml of human serum. An endogenous substance(s) which disturbed the immunoreaction and gave such an apparently high concentration of 6-ketoprostaglandin F1 alpha separated from the endogenous 6-ketoprostaglandin F1 alpha by HPLC. With the purified 6-ketoprostaglandin F1 alpha fraction there was a good correlation (r = 0.994) between enzyme immunoassay and radioimmunoassay. The validity of the enzyme immunoassay was confirmed by gas chromatography-selected ion monitoring.