Eight monoclonal antibodies, specific for the glycoprotein hormone α-subunit, were raised against human free α-subunit, human FSH, or human CG. All of these antihuman monoclonal antibodies were tested for cross-reactivity with α-subunits derived from bovine, porcine, equine, bull frog, sea turtle, turkey, and ostrich glycoprotein hormones. All showed cross-reactivity with affinities ranging from 10-4to 10-8depending upon the antibody and the species of α-subunit. Cyanogen bromide fragments of bovine and equine α, when tested with selected antibodies indicated that antigenic determinants could be localized in two regions: α9-33 and α76-92. Comparison of amino acid sequences, and relative potencies, suggest that major antigenic determinants involve residues 21, 22, and 23 (F-F-S in human α) and 76-85 (G-G-F-K-V-E-N-H-T-A in human α). As part of this study the N-terminal amino acid sequences of bull frog, sea turtle, turkey, and ostrich α-subunits were determined and reported for the first time.
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