FIGURE 1.

A, three-dimensional view of the complex of AHSP (green) and α-Hb (red). The molecular structure shows the position of the AHSP tryptophan residue Trp⁴⁴ (orange) and the valine (violet) that is mutated (V56G) in the clinical case. The image was obtained from the crystallographic structure of the AHSP·α-Hb complex (Protein Data Bank code 3ia3) using PyMOL software. B, composite kinetics of the AHSP association with α chains and subsequent replacement of AHSP by β chains at 37 °C, pH 7. Mixing ratios were 1:1 in each case at 10 μm final protein concentration. The β chain and AHSP were premixed and loaded in one of the stopped-flow syringes, for mixing with the α chains: [β-Hb + AHSP] + α-Hb → β-Hb + AHSP·α-Hb → AHSP + αβ. The fluorescence of the single tryptophan (Trp⁴⁴) residue of AHSP serves as a probe for the binding to α chains.