Concanavalin A affinity chromatography of human serum gonadotropins: evidence for changes of carbohydrate structure...

We have studied the carbohydrate of circulating human gonadotropins (FSH and LH) in different clinical conditions using Concanavalin A (Con A) affinity chromatography. This technique permits separation of molecules differing in the extent of carbohydrate branching. The proportion of molecules that does not bind to Con A was greater in circulating FSH than in LH, reflecting a higher content of multiantennary and/or bisected biantennary complex carbohydrate structures in serum FSH. No significant difference in gonadotropin binding pattern to Con A was found between normal controls and patients with chronic uremia or gonadotropin-secreting pituitary adenomas. On the contrary, sera from postmenopausal women and fetuses contained a greater proportion of FSH and LH that bound to Con A, indicating a shift from multiantennary and/or bisecting structures to hybrid and/or high mannose forms, i.e. to the secretion of less mature forms. International Reference Preparations, derived from pituitary extracts, were more retained on Con A than circulating hormones, suggesting that carbohydrate chains of the intrapituitary hormone stock are less mature than those present in the circulation. Less mature forms were also found in FSH, but not in LH, from normal controls after GnRH injection. Finally, a higher proportion of unbound forms, i.e. complex carbohydrate chains, was found in healthy subjects presenting with an immunologically anomalous variant of LH. In conclusion, the current data show that the hormonal status of the individual may differently affect carbohydrate branching of gonadotropins. Alteration in glycosylation is likely to be involved in masking at least one epitope specific for intact LH dimer, thus indicating that it may modulate the tertiary structure of glycoprotein hormones.