Fig. 6. (A) O₂ equilibrium curves of Thermarces cerberus Hbs I, II and III in the absence of added anions (solid lines), the presence of 0.1 mol l^-1 Cl^- (dashed lines) and the presence of 0.1 mol l^-1 Cl^- and saturating ATP concentration (20-fold excess over Hb tetramers; dotted lines). (B) Bohr effect plots. Buffer, 0.1 mol l^-1 Hepes; heme concentration, 0.16 mmol l^-1. (7.50 Torr=1 kPa.)