Effects of 2, 3-BPG on oxygen affinity of the Hb F variants. Oxygen affinities of recombinant Hb F (▵), Hb F γG1V, γS143H (□), and Hb F γG1V, γE5P, γS143H (○) were measured in 50 mmol/L Bis-Tris, pH 7.2, containing 5 mmol/L EDTA and 0.1 mol/L NaCl at 20°C as a function of various 2, 3-BPG concentrations, and results were compared with those of Hb A (•) and Hb F (▴) isolated from human adult and cord red blood cells, respectively.