Oxygen equilibrium curves of Hb A, Hb βG16D, K120E, and Hb βC112D were determined in 50 mmol/L Bis Tris buffer, pH 7.1 containing 0.1 mol/L NaCl at 20°C. P₅₀ is the partial oxygen pressure required to give 50% oxygen saturation of hemoglobin. n₅₀ values were calculated from the Hill plot of oxygen equilibrium curves. Concentration of 2, 3-BPG when present (+) is 2 mmol/L.