FIGURE 4.

Effects of 2,3-diphosphoglycerate (2,3-DPG), inositol hexaphosphate (IHP), and the sickle cell mutation, HbS, on the interaction of H₂S with MetHb. A and B, kinetics of decrease in MetHb concentration in 100 mm HEPES buffer, pH 7.4, 25 °C (detected at 405 nm) after the addition of 50 μm Na₂S to an aerobic solution of 2.5 μm MetHb with (red) or without (black) 5 mm 2,3-diphosphoglycerate (A) or 5 mm inositol hexaphosphate (B). C, clearance of H₂S by MetHb (1 mg/ml) in aerobic 100 mm HEPES buffer, pH 7.4, in the absence (○) or presence of 5 mm 2,3-diphosphoglycerate (□) or 5 mm inositol hexaphosphate (▵) at 25 °C. The data represent the average of two experiments. D, H₂S clearance by MetHbS (1 mg/ml) in 100 mm HEPES buffer, pH 7.4, at 25 °C. E, spectral changes elicited by binding of 0–60 μm Na₂S to 2.5 μm MetHbS in 100 mm HEPES buffer, pH 7.4, 25 °C. The final spectrum is shown in red and does not change with additional Na₂S aliquots.