All-or-none N-glycosylation in primate follicle-stimulating hormone β-subunits

Human FSH exists as two major glycoforms designated, tetra-glycosylated and di-glycosylated hFSH. The former possesses both α- and β-subunit carbohydrates while the latter possesses only α-subunit carbohydrate. Western blotting differentiated the glycosylated, 24,000 Mr hFSHβ band from the non-glycosylated 21,000 Mr FSHβ band. Postmenopausal urinary hFSH preparations possessed 75–95% 24,000 Mr hFSHβ, while pituitary hFSH immunopurified from 21- to 43-year-old females and 21–43-year-old males possessed only 35–40% 24,000 Mr hFSHβ. The pituitary hFSH from a postmenopausal woman on estrogen replacement was 75% 21,000 Mr hFSHβ. Other immunopurified postmenopausal pituitary hFSH preparations possessed 50–60% 21,000 Mr hFSHβ. Gel filtration removed predominantly 21,000 Mr free hFSHβ and reduced its abundance to 13–22% in postmenopausal pituitary hFSH heterodimer preparations. A major regulatory mechanism for FSH glycosylation involves control of β-subunit N-glycosylation, possibly by inhibition of oligosaccharyl transferase. Two primate species exhibited the same all-or-none pattern of pituitary FSHβ glycosylation.