Steroid receptors in the human prostate. 2. Some properties of the estrophilic molecule of benign prostatic hypertrophy.

Some physicochemical properties of the estrophilic ‘receptor’ of human benign prostatic hypertrophy were examined by agar gel electrophoresis. 1) Competition analyses revealed the high selectivity of the molecule for the naturally occurring estrogens but not for representatives of other classes of steroid hormones (androgens, corticosteroids, progesterone). This, coupled with the failure of an estrogen ‘receptor’-rich extract to exhibit detectable tissue specific binding of (³H) 5α-dihydrotestosterone suggests that prostatic androgen and estrogen receptors may have separate identities. 2) The molecule proved highly resistant to enzyme attack, a stability conferred by estradiol-17β rather than by the thiol reagent dithiothreitol. Its proteinaceous nature was finally demonstrated when extract was exposed to enzymes at 0°C prior to steroid addition. 3) Initial complex formation between estrogen and its ‘receptor’ protein was rapid and reached a plateau after 4 hours. Binding was greater at 0°C than 37°C.