Fig. 2. O₂ equilibria of (A) Hb I and (B) Hb II of Symenchelis parasitica measured in 0.1 mol l^-1 Hepes buffer at pH 7.2 in the absence of added anions (circles) and in the presence of either 0.1 mol l^-1 Cl^- (triangles) or 0.1 mol l^-1 Cl^- + saturating ATP concentration (ATP/tetrameric Hb ratio >100; diamonds), illustrating a large ATP effect and no Cl^- effect on Hb I and distinct effects of both effectors on Hb II. Heme concentrations were 0.10 mmol l^-1 (Hb I) and 0.05 mmol l^-1 (Hb II). (7.50 Torr=1 kPa.)