Interaction of ACTH synthetic fragments with rat adrenal cortex membranes

Synthetic peptide, corresponding to the amino acid sequence 11–24 of human adrenocorticotropic hormone (ACTH), was labeled with tritium (specific activity of 22 Ci/mmol). [3H]ACTH (11–24) was found to bind to rat adrenal cortex membranes with high affinity and specificity (Kd = 1.8 ± 0.1 nM). Twenty nine fragments of ACTH (11–24) have been synthesized and their ability to inhibit the specific binding of [3H]ACTH (11–24) to adrenocortical membranes has been investigated. Unlabeled fragment ACTH 15–18 (KKRR) was found to replace in a concentration‐dependent manner [3H]ACTH (11–24) in the receptor–ligand complex (Ki = 2.3 ± 0.2 nM). ACTH (15–18) was labeled with tritium (specific activity of 20 Ci/mmol). [3H]ACTH (15–18) was found to bind to rat adrenal cortex membranes with high affinity (Kd = 2.1 ± 0.1 nM). The specific binding of [3H]ACTH (15–18) was inhibited by unlabeled ACTH (11–24) (Ki = 2.2 ± 0.1 nM). ACTH (15–18) at the concentration range of 1–1000 nM did not affect the adenylate cyclase activity in adrenocortical membranes. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd.