HIGH MOLECULAR WEIGHT FORMS OF HUMAN ACTH ARE GLYCOPROTEINS

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Abstract
The RIA-ACTH [radioimmunoassay-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 2nd, designated intermediate RIA-ACTH, eluted between the void volume and standard human 1-39 ACTH (MW. 4541). An immunoreactive material designated little ACTH co-eluted 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 (< 8%) of intermediate RIA-ACTH from all sources bound to concanavalin A, with the exception of that in the pitutary, of which 19% bound to the column and was subsequently recovered. The little ACTH from all sources was essentially excluded (> 93%) from the column. A significant fraction of human big RIA-ACTH is probably a glycoprotein, and human intermediate RIA-ACTH may be also.

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