Analysis of Human Pituitary and Tumor Adrenocorticotropin Using Isoelectric Focusing*

Abstract

Heterogeneity of immunoreactive ACTH was investigated in extracts of three human pituitary glands, three tumors obtained from patients with the ectopic ACTH syndrome, and a porcine pituitary gland using gel filtration and isoelectric focusing. A single gel filtration fraction of immunoreactive ACTH was applied to isoelectric focusing and pis were measured using RIAs specific for the amino-terminal portion (N-ACTH) and for the carboxyl-terminal (C-ACTH) of ACTH. The little ACTH peak of the human pituitary extract separated on gel filtration was found to contain four components with different pis on isoelectric focusing. The distribution of these peaks was almost identical in each pituitary extract, and the major peak in each case showed a pi value of 8.0, a value similar to that of synthetic human ACTH. The little ACTH peak of the tumor extract was composed of four or five peaks with different pi values. Each peak of the tumor extracts corresponded to some peak found in the pituitary extracts, and there was no peak specific for tumor. The C-fragment peaks in the tumor extracts and in the middle and posterior lobe extract of porcine pituitary, corresponding to corticotropin-like intermediate lobe peptide, showed a single peak with a pi of 5.2 and were different from the acidic forms of immunoreactive ACTH found in the little ACTH peak. These data indicate that isoelectric focusing is useful for examining microheterogeneity of immunoreactive ACTH with a similar molecular size when employed in conjunction with gel filtration. (J Clin Endocrinol Metab48: 559, 1979)