Progesterone-binding components of chick oviduct. Receptor B subunit protein purified to apparent homogeneity from laying hen oviducts.

The progesterone receptor B subunit has been purified to apparent homogeneity from hen oviduct cytosol using ammonium sulfate precipitation and chromatography on DEAE-cellulose, phosphocellulose, hydroxylapatite, and gel filtration on Agarose A-1.5m. The material is obtained (1 mug of purified protein/g of tissue) in about 17% yield. The protein is highly purified; a single band is seen on gel electrophoresis in acid-urea and sodium dodecyl sulfate gels as well as gel electrophoresis under nondenaturing conditions. In the latter system, labeled progesterone co-migrates with the protein band, demonstrating that the isolated protein is a progesterone-binding species. Labeled progesterone bound to the protein is displaced by progestational steroids but not by estradiol or hydrocortisone. The protein has a molecular weight of 116,000 g/mol as determined by gel electrophoresis and has a single polypeptide chain. The isolated protein contains 98% endogenous nonradioactive progesterone and is 2% labeled by incubation in vitro with radiolabeled progesterone. It behaves identically on all of the chromatographic steps to chick receptor B subunits described in earlier publications.