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An Unusual Sex Steroid-Binding Protein in Mature Male Rat Liver Cytosol^*

Department of Pharmacology and Reproductive Biology Section, Department of Obstetrics and Gynecology, Yale University, School of Medicine New Haven, Connecticut 06510>

Address all correspondence and requests for reprints to: Robert B. Dickson, Department of Pharmacology, Yale University, School of Medicine, 333 Cedar Street, New Haven, Connecticut 06510.

Abstract

Mature male rat liver cytosol contains a moderate affinity and capacity estrogen-binding protein in at least a 200-fold higher level than mature female or immature male rat liver cytosol. Binding of estradiol to this protein is very rapid, is stabilized by EDTA, and is inhibited by divalent cations. This is the major binding protein for [³H]estradiol ([³H]E₂) in mature male rat liver cytosol, and it has properties clearly distinguishing it from putative liver or uterine estrogen receptors. In addition to binding [³H]E₂, this protein seems to rapidly bind a [³H]5-dihydrotestosterone ([³H]DHT) metabolite at the same binding site. The binding of this androgen metabolite is stabilized by EDTA and is inhibited by divalent cations. The binding properties of the [³H]DHT metabolite suggest that these binding sites are not classical androgen receptors. Cytosol binding levels of both the [³H]E₂ and the [³H]DHT metabolites change in a similar direction in response to endocrine manipulation. The putative liver estrogen receptor level, determined after partial purification (in a redissolved 30% ammonium sulfate-precipitated fraction), seems to change in an opposite direction in response to these same endocrine manipulations.

Footnotes

^* This work was supported by NIH Grants HD-8280 and CA-08341.

Received November 12, 1977.