Characterization of biologically active bovine pituitary FSH purified by immunoaffinity chromatography using a monoclonal antibody

A substantial amount of highly purified, biologically active bovine FSH was isolated from pituitary extracts by immunoaffinity chromatography based on a novel anti-bovine FSH β-subunit monoclonal antibody. The biological activity was assessed in vitro using a steroidogenic granulosa cell line constitutively expressing the FSH receptor. Amino acid analysis, N-terminal amino acid sequencing, and peptide mass mapping demonstrated that primary structure modifications do not contribute to the heterogeneity of bovine FSH. The monosaccharide composition of the N-linked oligosaccharides was quantified and remarkably two distinct forms of sialic acids, N-acetyl- and N-glycolyl-neuraminic acids were found. In conclusion, we showed that isoform differences in bovine FSH is likely due only to sugar chain heterogeneity, and we give the first evidence that two substituted sialic acids contribute to the diversity of mammalian glycoprotein hormone isoforms.