Hypo-glycosylated human follicle-stimulating hormone (hFSH^21/18) is much more active in vitro than fully-glycosylated hFSH (hFSH²⁴)

Hypo-glycosylated hFSH^21/18 (possesses FSHβ²¹ and FSHβ¹⁸bands) was isolated from hLH preparations by immunoaffinity chromatography followed by gel filtration. Fully-glycosylated hFSH²⁴ was prepared by combining the fully-glycosylated FSHβ²⁴ variant with hCGα and isolating the heterodimer. The hFSH^21/18 glycoform preparation was significantly smaller than the hFSH²⁴ preparation and possessed 60% oligomannose glycans, which is unusual for hFSH. Hypo-glycosylated hFSH^21/18 was 9- to 26-fold more active than fully-glycosylated hFSH²⁴ in FSH radioligand assays. Significantly greater binding of ¹²⁵I-hFSH^21/18 tracer than hFSH²⁴ tracer was observed in all competitive binding assays. In addition, higher binding of hFSH^21/18 was noted in association and saturation binding assays, in which twice as much hFSH^21/18 was bound as hFSH²⁴. This suggests that more ligand binding sites are available to hFSH^21/18 in FSHR than to hFSH²⁴. Hypo-glycosylated hFSH^21/18 also bound rat FSHRs more rapidly, exhibiting almost no lag in binding, whereas hFSH²⁴ specific binding proceeded very slowly for almost the first hour of incubation.