Γ-MELANOTROPHIN-LIKE IMMUNOREACTIVITIES IN HUMAN PITUITARIES, ACTH-PRODUCING PITUITARY ADENOMAS, AND ECTOPIC ACTH-PRODUCING TUMOURS: EVIDENCE FOR AN ABNORMALITY IN GLYCOSYLATION IN ECTOPIC ACTH-PRODUCING TUMOURS

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Abstract
Using gel exclusion chromatography on Bio-Gel P-60, γ-melanotropin-like immunoreactivity (γ-MSH-LI) in three human pituitary glands, two ACTH-producing pituitary adenomas, and three ectopic ACTH-producing tumours (two medullary thyroid carcinomas and one thymoma) was divided into one or two molecular weight classes. The largest component eluted near the position of mouse 16K fragment and was designated big γ-MSH-LI. This big γ-MSH-LI was present in all samples. The second one, designated intermediate γ-MSH-LI, eluted between the position of mouse 16K fragment and human ACTH, and was demonstrated only in two ectopic ACTH-producing tumours. No γ-MSH-LI emerged at the elution position of synthetic γ3-MSH. Affinity chromatography on concanavalin A-agarose revealed that a significant fraction (52–68%) of γ-MSH-LI from human pituitary glands, ACTH-producing pituitary adenomas, and one ectopic ACTH-producing tumour bound to the column and was eluted with α-methyl-D-mannopyranoside. In two ectopic ACTH-producing tumours which contained big and intermediate γ-MSH-LI, a relatively small fraction (27–35%) of γ-MSH-LI bound to the column and was similarly eluted. These observations suggest that human γ-MSH-LI is glycosylated and that there is an abnormality in the glycosylation of γ-MSH-LI in some ectopic ACTH-producing tumours.