Inhibition of adrenocorticotropin effects on adrenal cell membranes by synthetic adrenocorticotropin analogues: correlation of binding and adenylate cyclase activation

Ways, D.K.; Zimmerman, C.F.; Ontjes, D.A.

Molecular Pharmacology 12(5): 789-799


ISSN/ISBN: 0026-895X
PMID: 186700
Accession: 068523342

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Human ACTH and a number of ACTH peptide fragments were prepared by solid-phase synthesis. Of the analogues tested, only ACTH1-39 and ACTH1-24 stimulated rat adrenal membrane adenylate cyclase in vitro. Several shorter fragments, including ACTH6-39, ACTH9-24, ACTH9-19 amide, ACTH9-20, ACTH9-18 and ACTH12-39, inhibited stimulation of the enzyme by native bovine ACTH. The inhibition produced by this group of peptides appears to be specific for ACTH-stimulated adrenal adenylate cyclase. Basal and Fluoride-stimulated enzyme activity in adrenal and Fluoride or epinephrine-stimulated activity in liver were not inhibited by ACTH9-24. To elucidate further the action of the inhibitory peptides, their ability to inhibit the binding of [125I]ACTH1-24 to adrenal particles was tested. Peptides having either agonist or antagonist activity in the adenylate cyclase assay were effective competitors for binding. The order of potency according to both adenylate cyclase inhibition and competitive binding affinity was ACTH6-30 > ACTH9-19 amide .simeq. ACTH9-24 > ACTH9-20 .simeq. ACTH9-18 > ACTH12-39. The analogues ACTH1-8, ACTH9-16 and ACTH19-39 were inactive in both the adenylate cyclase and binding systems. Comparison of this series of closely related peptides in 2 independent assay systems should more clearly define the structural requirements for the binding of ACTH to its membrane receptor.