Immunologic studies of adrenocorticotropic hormone (ACTH): effect of carboxypeptidase digestion on biologic and immunologic activities.

Abstract

Abstract The radioimmunologic activity of ovine ACTH (αs-ACTH) and a C-terminal (αs22–39-ACTH) fraction of ovine ACTH before and after carboxypeptidase digestion was studied with 2 antiporcine and 2 antiovine ACTH sera. The amino acids released after carboxypeptidase digestion were measured. These were mainly the C-terminal phenylalanine and only traces of glutamic acid and leucine. With the 2 antiporcine ACTH sera, the immunologic activity of αs-ACTH and αs22–39-ACTH was almost completely abolished by carboxypeptidase treatment. The steroidogenic activity of ACTH was unchanged. This is a further example of the dissociation in immunologic and biologic activities of ACTH. With 2 antiovine ACTH sera, the results were different: carboxypeptidase treatment caused only a slight decrease in immunologic activity of αs-ACTH but a marked decrease in that of αs22–39-ACTH. It is concluded that the C-terminal phenylalanine is necessary for the binding of ACTH peptides with the antiporcine ACTH sera studied. While the...