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HIGH MOLECULAR WEIGHT FORMS OF HUMAN ACTH ARE GLYCOPROTEINS

Department of Medicine and Cancer Research Center, Vanderbilt University School of Medicine, Nashville Tennessee 37232

The RIA-ACTH in a normal human pituitary, 2 ectopic ACTH-secreting tumors and plasma from a patientr 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 -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. These data indicate that a significant fraction of human "big" RIA-ACTH is a glycoprotein and that human "intermediate" RIA-ACTH may be also.

Supported by grants from the National Institutes of Health: 5-ROI-AM-05318 and 8-MOI-RR95, and National Cancer Institute Grant 5-ROI-CA11685

Received November 15, 1976.

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