Activation of the chick oviduct progesterone receptor by heparin in the presence or absence of hormone

Abstract

Activation (transformation) of the chick oviduct progesterone receptor was induced at 0.degree. C by heparin free in solution and by chromatography on a column of heparin linked to acrylamide/agarose. The transformed molecule displayed properties of the activated form of [3H]progesterone-receptor complex obtained by heat treatment or by high ionic strength: smaller size (s20,w = 3.9 S, Stokes radius = 5.2 nm), lower rate of dissociation (t1/2 .apprx. 50 h at 0.degree. C compared with .apprx. 20 h for the ''native'' form) and increased binding to phosphocellulose. In all cases, molybdate was an effective inhibitor of transformation and stabilized a large ''native'' form (s20,w = 7.9 S, Stokes radius = 7.6 nm). Transformation by neither KCl nor heparin depended on the presence of ligand bound to the receptor, and the properties of the receptor molecule produced by treatment of ligand-free receptor with high ionic strength or with heparin were identical with those of the activated progesterone-receptor complex, demonstrating that receptor activation can be obtained experimentally in the absence of hormone. The data are compatible with a model in which activation implies separation of the 4S units, which compose the .apprx. 8 S ''native'' form.