High molecular weight forms of immunoreactive ACTH in a human pituitary and ectopic ACTH-producing tumors

High molecular weight forms of immunoreactive ACTH (IR-ACTH) were studied in a human pituitary gland and 4 ectopic ACTH-producing tumors in man. Both the pituitary and tumor extracts contained "big" IR-ACTH, which eluted near the void volume, and a small amount of "intermediate" IR-ACTH components, which eluted between the void volume and 125I-alpha h1-39 ACTH, in addition to "little" ACTH which coeluted with 125I-alpha h1-39ACTH by Sephadex G-100 gel filtration. A significant amount of the "big" IR-ACTH applied bound to the concanavalin A-agarose column and was eluted with 0.2 M alpha-methyl-D-mannopyranoside, indicating the glycoprotein content of "big" IR-ACTH fractions. When the "big" and "intermediate" fractions were further analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, they were resolved into 4 molecular forms of IR-ACTH with apparent molecular weight of 37,000, 24,000 , 18,000 and 4,500, respectively. These results indicate that 3 high molecular forms of IR-ACTH are present in the human pituitary and the ectopic ACTH-producing tumors.