The Intranuclear Binding of Testosterone and Sa-AndrostanX’@-ol-5one by Rat Prostate*

The intranuclear binding of radioactive hormone in prostate after the intravenous administration of testosterone-l ,2-3H to rats has been studied. Nuclei obtained by sucrose density gradient centrifugation were extracted with buffer containing 0.6 M NaCl, and the soluble radioactivity was separated into bound and free fractions by gel filtration on Sephadex G-25 or G-ZOO. As early as 15 min after testosterone administration, the radioactivity recovered in the bound form was predominantly dihydrotestosterone. By gel filtration of nuclear extracts on Sephadex G-ZOO and by the use of digestive enzymes, it was shown that dihydrotestosterone was bound to an acidic nuclear protein. Finally, several characteristics of this binding phenomenon were defined; the binding was stable to freezing for as long as 8 days, stable to short term incubation at 20” but not at 37”, and partially stable to repeated gel filtration on Sephadex.