Effect of Modification of N-Acetylneuraminic Acid on the Biological Activity of Human and Ovine Follicle-stimulating Hormone

Ovine and human follicle-stimulating hormone (FSH) were modified by periodate oxidation followed by borohydride reduction, yielding FSH-containing analogues of N-acetylneuraminic acid (NANA) shortened by 1 or 2 carbon atoms. The FSH activity of the modified preparations was assayed by the human chorionic gonadotropin augmentation assay. The treatment decreased the biological activity of FSH somewhat, but, even when no unmodified NANA remained, the potency was still about half that of untreated FSH. Treatment of either native or modified FSH with neuraminidase resulted in the release of all NANA and NANA-8 and some NANA-7, and the loss of hormonal activity. It appears, therefore, that an intact 3-carbon polyhydroxy side chain in NANA is not required for full FSH activity.