Isolation and Characterization of Subunits from Equine Pituitary Follicle-stimulating Hormone

Equine follicle-stimulating hormone (FSH) was dissociated into two noncovalently linked subunits, α and β. This was accomplished by incubation of FSH in 8 m urea at 37° for 20 hours followed by ion exchange chromatography on DEAE-Sephadex A-50. This resulted in complete separation of the subunits. The individual subunits were purified by gel filtration on Sephadex G-100 columns. The results of the physicochemical characterization studies indicated that these subunits were nonidentical. Both α and β had a high threonine and glutamic acid content, but differed in the content of other amino acids. The sum of the amino acid contents of the two subunits agreed well with the amino acid composition of the intact FSH. The molecular weights of the subunits were similar, each being approximately 16,000. There was dissimilarity in the electrophoretic mobilities, although both subunits exhibited microheterogeneity. Examination of the carbohydrate content showed that the β subunit contained approximately 5% more total carbohydrate than did the α subunit. Biological activity was absent in each of the subunits, but after recombination 56% of the original FSH activity was recovered. The α subunits of equine FSH, human FSH, and human chorionic gonadotropin showed great similarity, suggesting homology. The β subunits of these hormones showed numerous differences, possibly accounting, at least in part, for the specificity of the hormone.