Nuclear binding of 5α-dihydrotestosterone in the male rat pituitary: Evidence for two binding forms

Abstract

Purified nuclei were prepared from prepubertal male rat pituitaries incubated at 37°C in the presence of [1,2- 3H]-5α-DHT, and selectively extracted with saline solutions of different ionic strength and pH. This extraction process led to the identification of two nuclear 5α-DHT receptor complexes : one soluble in the nuclear sap, the other bound to chromatin. Their relative amount and their specific activity (362 fmol/mg protein and 38 fmol/mg protein, respectively), were determined after precipitation by a protamine sulphate solution. These two kinds of nuclear 5α-DHT receptor complexes were characterized using sucrose gradient centrifugation and Sephadex G-200 gel chromatography. The soluble nuclear sap 5α-DHT binding component sedimented as a 5.6S entity and was retained on Sephadex G-200 gel, whereas the complex bound to chromatin sedimented as a 4.6S entity and appeared in the void volume of the Sephadex G-200 gel column. Both are hormone specific proteins, and are distinct from the cytosol 5α-DHT complex. The physiological role of these two forms is not yet determined.