Hydrodynamic properties of the angiotensin II receptor from bovine adrenal zona glomerulosa

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Abstract
The bovine adrenal angiotensin II receptor was solubilized with the non-ionic detergent octyl β-D-glucoside following its binding with the high-affinity antagonist 125I-labelled [Sar1,Ile8]angiotensin II. The complex was sufficiently stable to allow the determination of its hydrodynamic properties. The solubilized receptor migrated on a Superose 6 column as a single peak with a Stokes radius of 5.29 nm. Comparison of sedimentation behaviour through a sucrose density gradient in H2O and 2H2O lead to a partial specific volume of 0.751 ml/g and a sedimentation coefficient (S20,w) of 5.17 S. Combination of gel filtration and sedimentation data indicated that the labelled protein-detergent complex has an Mr of 124,000 and a frictional ratio of 1.42. The Mr of the angiotensin II receptor was estimated as 104,000 kDa after correction for the bound detergent. Photoaffinity cross-linking of 125I-[Sar1, (4-N3)Phe8]angiotension II with bovine adrenal membrane receptor followed by SDS/PAGE under reducing and non-reducing conditions yielded a broad band of Mr 54,000. This suggests that the angiotensin II receptor is a non-covalent dimer in which the two subunits have a similar Mr.