Isolation and amino acid sequence of the alpha-subunit of follicle-stimulating hormone from equine pituitary glands.

Six hundred milligrams of follicle-stimulating hormone (FSH), containing 110 NIH-FSH-S1 units/mg, was isolated from 9 kg of equine pituitary glands. The equine FSH was dissociated into alpha- and beta-subunits. A tentative amino acid sequence of the alpha-subunit was determined. The alpha-subunit contained 82 amino acids. The equine FSH-alpha is shorter by 10 to 14 amino acids at the NH2 terminus and has several substitutions at several positions as compared with human FSH-alpha and bovine thyroid-stimulating hormone-alpha. At the intraspecies level, the alpha-subunits of human FSH, human luteinizing hormone, and human chorionic gonadotropin are similar, whereas at the interspecies level there are differences among the alpha-subunits of FSH, luteinizing hormone, and thyroid-stimulating hormone.