Corticosteroid receptors in the kidney of chick embryo I. Nature and properties of corticosterone receptor

Abstract

Cytosol from kidney of chick embryo (age 16–18 days) contained a corticosterone-binding site with the features of a putative receptor. This receptor was a thermolabile protein, readily digested by proteolytic enzymes, with a sedimentation coefficient of 7–8 S and with an apparent molecular weight greater than 100,000. Simultaneous studies with transcortin (CBG) revealed several differences between the renal- and serum-binding protein pertaining to the effect of temperature, the sedimentation coefficient, the charcoal “stripping”and, finally, the binding and competition of various steroids for the two proteins. Kinetic analysis showed a rapid association (10 min), which followed second-order reaction kinetics, and a dissociation of pseudo-first-order reaction kinetics with a t 1 2 , of168 min at †. The analysis of the Scatchard plot showed the presence of a single class of binding sites with an association constant ( K A ) of 1.3 × 10 8 M −1 and a binding capacity ( n max) of 500–700 fmoUmg protein. We obtained similar results when we used dexamethasone as a ligand. The association ( k a ) and dissociation ( k d ) rate constants were respectively 2.9 × 10 6 M −1 sec −1 and 6.86 × 10 −5 sec −1. From their ratio a K A value of 4.2 × 10 10 M −1 was obtained. Studies with various steroids demonstrated that only dexamethasone and, to a lesser degree, progesterone competed for the binding site. These data showed that the kidney of chick embryo possessed one type of receptor for the glucocorticoids, which was similar to the type II described in rat kidney.