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

Publisher Website
Google Scholar
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.