Cytosol androgen receptor (AR) in human skin fibroblasts: characterization of the binding reaction and differentiation from androgen binding molecules of lower affinity

Androgen binding was studied in cytosol of human fibroblasts at 4 degrees C. When 5 alpha-dihydrotestosterone (DHT) was the ligand, a curvilinear Scatchard plot was seen, which was resolved into two components: I the androgen receptor (AR), Kd = 0.12-0.44 nM, and II a low affinity species, Kd = 6.3-28 nM. The same cytosol demonstrated only type I binding for 3H-methyltrienolone (MTr), Kd = 0.10-0.40 nM. The AR, i.e., 3H-MTr binding activity, eluted at 440,000 d by gel filtration chromatography in pre-labeling and post-labeling experiments. When the ligand was 3H-DHT, binding activity in the 10,000-45,000 d range was seen in addition to AR. Thus, saturable nonreceptor steroid binding was seen for DHT but not for MTr. The latter is the preferred ligand for the study of the AR in this system.