Binding affinity of tetrameric coho salmon Ig anti-hapten antibodies

Tetrameric Ig anti-fluorescyl antibody was purified from sera of immunized coho salmon by immunoadsorption and the ligand binding properties studied from a series of bleedings over a 120-day period. Purified antibody was assayed by fluorescence quenching and equilibrium dialysis for determination of the average intrinsic association constant (K_a) and heterogeneity index (a). All antibody preparations showed an equilibrium constant of ~4–5 × 10⁵ M⁻¹ for the fluorescyl ligand, regardless of the time of bleeding after primary or secondary immunizations. Heterogeneity indices, derived from Sips plots, indicated relatively restricted heterogeneity in all purified antibody populations. The ligand binding results are discussed in terms of apparent restricted regulatory functions in salmon with respect to affinity maturation.