Absorption and circular dichroism spectra of Hb F and the two Hb F variants. Absorption (A) and CD (B) spectra were recorded for the CO forms of human and recombinant Hb F and the two Hb F variants in 0.1 mol/L phosphate buffer, pH 7.0, at 5°C. Results were corrected for small differences in protein concentration. a, b, c, and d represent Hb F purified from cord blood, yeast, and the two purified Hb F variants (Hb F γG1V, γS143H and Hb F γG1V, γE5P, γS143H), respectively.