Androgen-binding proteins in sheep epididymis: characterization of a cytoplasmic androgen receptor in the ram epididymis.

An androgen receptor (Rc) was demonstrated in caput, corpus and cauda epididymal cytosols of the ram. This receptor had a high affinity for 5 alpha-dihydrotestosterone (Kd = 5.2 X 10(-9) mol/l) and could be distinguished from the androgen-binding protein (ABP) by several characteristics. On polyacrylamide-gel electrophoresis, Rc had a mobility of 0.37 and ABP 0.61; Rc sedimented in the 9S region of a linear sucrose gradient whereas ABP migrated in the 4.3S region; the molecular weights were 192 000 and 90 000 for Rc and ABP; their isoelectric points were 5.7 and 4.8-5.0; they were proteinaceous components since they were destroyed by proteolytic enzymes and heating (50 degrees C for Rc and 60 degrees C for ABP); they exhibited different half-times of dissociation:20 h at 0 degree C for Rc and 6 min for ABP, which is in agreement with their respective physiological roles, intra- and extracellular transport of androgens. The content of Rc-binding sites in caput epididymis was 18, in corpus 4 and in cauda 22 fmol/mg protein.