Localization of an Adrenocorticotropic Hormone Receptor on Bovine Adrenal Cortical Membranes

The preparation of a subcellular fraction from bovine adrenal cortex is described. Characterization by electron microscopy, electron microscopic cytochemistry, and enzymatic assay indicates that this fraction is enriched plasma membranes. The preparation binds the steroidogenically active [Gln5] [14C-Phe7] corticotropin1–20 amide. The specificity of this binding is demonstrated by competitive binding studies with pig corticotropin as well as adrenocorticotropic hormone (ACTH) fragments and analogs. The membrane preparation contains an adenylate cyclase sensitive to both sodium fluoride and corticotropin1–24. Corticotropin11–20 amide binds to the membranes but fails to activate adenylate cyclase. This membrane preparation provides a means to correlate peptide structure and in vivo corticotropic activity with selective binding and adenylate cyclase activation. The observation that corticotropin11–20 amide binds to the membranes but does not activate the adenylate cyclase supports the previous hypothesis that major binding sites of the ACTH molecule reside in this portion of the sequence. Two peptides exhibiting significantly higher in vivo adrenocorticotropic activity than ACTH from natural sources were only weakly active in stimulating the membrane adenylate cyclase. The experimental results strongly suggest that the membrane preparation contains an ACTH receptor.