Corticosteroid receptors in the kidney of chick embryo: III. Nature, properties, and ontogeny of aldosterone receptor

Abstract

An aldosterone receptor in the cytosol from kidney of chick embryos which had a sedimentation coefficient of 8.2 S and a molecular weight higher than 100,000 was identified. Kinetic analysis at 4° revealed a rapid association of the hormone to the receptor that followed second-order reaction kinetics and a dissociation of pseudo-first-order reaction kinetics. The association ( k a) and dissociation ( k d) rate constants were, respectively, 4.94 × 10 5 M −1 sec −1 and 8.33 × 10 −6 sec −1. From their ratio a K A value of 5.9 × 10 10 M −1 was calculated. In a series of experiments performed with kidneys of 17-day-old embryos, the K A at equilibrium, obtained from the Scatchard plot, was 3.1 ± 1.2 × 10 8 M −1, whereas the N max was 172 ± 14 fmol/mg protein. Competition studies with various steroids demonstrated that corticosterone had an affinity for the receptor close to that of aldosterone, thus suggesting a degree of resemblance of the mineralo- and glucocorticoid receptors in the chick embryo. However, the profiles of the binding affinities and capacities during the embryogenesis showed that the aldosterone-binding sites had a pattern completely different from that of the glucocorticoid receptor, indicating that the two receptors are most likely separate entities.