Characterization of a cytoplasmic androgen receptor in the ram testis

Abstract An androgen receptor has been characterized in the cytosol fraction of testes from hypophysectomized adult rams after in vitro labelling with [ 3H ]testosterone. It can be distinguished from the testicular androgen-binding protein (ABP) and from the plasma 5α-dihydrotestosterone-binding protein by electrophoresis on 3.25% acrylamide gels ( R x = 0.5) and on agar gels (anodic migration). It sediments in the 4S region in sucrose gradient containing 0.4 M KC1. Its complex with testosterone dissociates very slowly ( t 1 2 = 29 h at 0°C), and is destroyed by heating at 50°C for 30 min and by pronase. Its relative affinities for steroids are 5α-DHT > T > 5α-androstanediols > cyproterone acetate > estradiol > progesterone. The number of binding sites is limited (about 20 fmoles/mg protein) and the apparent equilibrium dissociation constant ( K D ) is 5 × 10 −9 M.