O₂-affinities, anion sensitivities, and pH sensitivities of duck HbA isoforms with alternative residues at β94 (derived Glu in high-altitude taxa, and ancestral Asp in low-altitude taxa).

O2-affinity was measured as P50 (torr, mean ± SEM), anion sensitivity was measured as the difference in log-transformed P50 values in the presence and absence of anionic effectors (Δlog P50([KCl+IHP]—stripped)), and pH sensitivity was measured by the Bohr factor (Φ = Δlog P50/ΔpH). All measurements were conducted at 37°C, pH 6.9–7.4 (as indicated) in 0.1 M HEPES buffer in the absence and simultaneous presence of Cl- ions (0.1 M KCl) and IHP (at two-fold molar excess over tetrameric Hb); [Heme] = 0.300 mM.