BIOTIN-LABELED AND PHOTOACTIVATABLE ALDOSTERONE AND PROGESTERONE DERIVATIVES AS LIGANDS FOR AFFINITY-CHROMATOGRAPHY, FLUORESCENCE IMMUNOASSAYS AND PHOTOAFFINITY-LABELING

New derivatives of progesterone and aldosterone were synthesized and f unctionally tested with commercially available antibodies. The covalen t labelling of antibodies specific for aldosterone and progesterone wa s detected by SDS/PAGE analysis and subsequent autoradiography after u sing mino-(3-[I-125]iodo-4-azidosalicylamidobutylamine) derivatives of aldosterone and progesterone, respectively, as photoactivatable radio ligands. Labelling was not observed in the presence of an excess of th e unlabelled steroid. Aldosterone was labelled with biotin and used as a tracer in a time-resolved fluorescence immunoassay. The nonradioact ive tracer is highly selective for its antibody-binding site, with alm ost no detectable cross-reactivity for other steroids. Biotin-labelled progesterone was immobilized by avidin-agarose and used for affinity chromatography. This yielded a more than 20-fold enrichment of an anti -progesterone polyclonal antibody. These results demonstrate that deri vatives of steroids are particularly useful for the development of non radioactive assays for the determination of natural steroids and may b e also useful for the detection of specific binding sites in biologica l material such as plasma membranes.