Effects of urea and molybdate on the chick oviduct progesterone receptor

Abstract

1. 1. The chick oviduct cytosol progesterone receptor, when complexed with ligand, can be exposed to urea concentrations as high as 3 M (at 0°C) without loss of steroid binding capacity. The ligand dissociation rate is increased ≥ 10 fold under these conditions. 2. 2. The “native” 8 S form of the receptor is progressively converted to a 4 S species by urea (> 2M) as seen in ultracentrifugation analysis. This conversion is inhibited by Na 2MoO 4 (5–50 mM) suggesting that molybdate stabilizes the 8 S molecule by direct interaction. 3. 3. At urea concentrations above 2 M, the ligand-free receptor looses progressively its binding capacity. The “transformed”, 4 S receptor was less stable than the 8 S species, and could not be protected by molybdate.