High molecular weight forms of human ACTH are glycoproteins.

The RIA-ACTH in a normal human pituitary, 2 ectopic ACTH-secreting tumors and plasma from a patient with Nelson's syndrome and one with ectopic ACTH syndrome was divided into 3 molecular weight classes after gel exclusion chromatography. The largest component appeared in or near the void volume and was designated "big" RIA-ACTH. The second, designated "intermediate" RIA-ACTH, eluted between the void volume and standard human 1-39 ACTH (mol. wt. 4,541). An immunoreactive material designated "little" ACTH-coeluted with standard human ACTH. A significant fraction (29-61%) of "big" RIA-ACTH from the tumors bound to concanavalin A-agarose and was eluted with 0.2 M alpha-methyl-D-mannopyranoside. An additional 16-22% of "big" RIA-ACTH was more tightly bound to the concanavalin A, but could be purged from the column with 0.1 M acetic acid. A smaller total percent of "big" RIA-ACTH from the pituitary (20%) and plasmas (5-10%) bound to the lectin and was similarly eluted and purged. Relatively little (less than 8%) of "intermediate" RIA-ACTH from all sources bound to concanavalin A, with the exception of that in the pitull sources was essentially excluded (greater than 93%) from the column. These data indicate that a significant fraction of human "big" RIA-ACTH is a glycoprotein and that human "intermediate" RIA-ACTH may be also.