SOLUBILIZATION AND CHARACTERIZATION OF ACTIVE ANGIOTENSIN II RECEPTORS FROM THE BOVINE ADRENAL CORTEX

Abstract

Binding sites showing the characteristics of receptors for angiotensin II have been solubilized with the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) from bovine adrenal membranes. Binding of ¹²⁵I-angiotensin II to the solubilized receptor was of high affinity and saturable. Angiotensin II analogs inhibited the binding competitively, whereas unrelated peptides did not. Binding activity of the receptor was completely abolished by treatment with the disulfide-reducing agent β-mercaptoethanol. In CHAPS, the receptor formed a complex with ¹²⁵I-angiotensin II, which is sufficiently stable to permit physicochemical characterization. The CHAPS-solubilized receptor has a Stokes radius of 7.5 nm when measured by gel filtration on Ultrogel AcA 34. On isoelectric focusing, ¹²⁵I-angiotensin-receptor complexes gave a major (pI=6.1) and a minor (pI=4.3) peaks. Angiotensin II-bound and free receptors exhibited marked differences in their stability against acid and β-mercaptoethanol.