Association Constant and Specificity of Oestradiol-receptor Interaction

Abstract

IT was shown¹ that strips of immature calf uterus incubated in vitro in the presence of 10⁻⁹ M ³H-oestradiol-17β concentrate the hormone 400 per cent or more; about 80 per cent of the radioactivity in the tissue is found associated strongly but non-covalently with the nuclear fraction and consists of intact 17β-oestradiol; treatment of the nuclear fraction with 0.4 M KCl at pH 8.5, as already applied by us to rat², solubilizes an oestradiol-macromolecule complex which sediments at about 5S; the macromolecule is protein, or at least the moiety binding the hormone is protein. A similar 5S oestrophilic component from calf uterus was obtained by Jungblut et al.³. Recent studies^4–6 suggest that the 5S macromolecule originates from the 8–10S macromolecular component which binds 17β-oestradiol and is found in the high speed supernatant of uterus.