Specific binding of androgen and androgen-receptor complex by microsomes from rat ventral prostate

Abstract

Microsomes from rat ventral prostate show the presence of a high affinity-low capacity population of androgen-binding sites with affinity for ionic exchange resin similar to that of cytosol androgen receptor (AR), as manifested by similar results obtained with hydroxylapatite. The affinity for mibolerone was similar for both forms ( K a =0.5–2.9 × 10 10M −1). The membrane-bound form can be extracted in hypotonic buffer, with retention of binding properties. Isotonic sucrose allowed higher degree of extractability of the microsomal AR than 10% (v/v) glycerol. The presence of hormone lends stability to the microsomal AR, while high salt or nonionic detergents have a deleterious effect on their longevity. The microsomal receptor form is not sensitive to serine-proteases as opposed to the cytosol AR. After exhaustive extraction of binding sites, microsomes are capable of accepting cytosol mibolerone-receptor complexes to a level corresponding to the concentration of depleted binding sites; microsomes from non-target tissue do not manifest such capability. Microsomal AR complexes do not bind DNA and they are not activated after heat treatment. Mixed preparations of extracted microsomal complexes with cytosol complexes showed heat-induced increased ability to bind DNA to the same level of diluted cytosol complex alone, indicating the absence of a microsomal inhibitor of DNA binding. The results indicate the co-existence of a non-DNA binding form of the AR in the microsomal membranes with the classical DNA binding form of the AR present in the cytosol of ventral prostate homogenates.