β^S-chain exchange as a function of incubation time with Hb β112 Cys→Asp tetramers. Tetrameric Hb βC112D was incubated with β^s chains in 0.1 mol/L phosphate buffer, pH 7.0 at 25°C, and Hb S tetramer formation, as well as generation of β112 Cys→Asp chains, were analyzed by FPLC. (A), (B), and (C) correspond to chromatographic analyses before (zero time point) and after 15 and 30 minutes incubations in the presence of β^s chains, respectively. Peaks a, b, c, and d represent β112 Cys→Asp, Hb βC112D, Hb S and β^S, respectively. The dotted line is a trace of the gradient profile for NaCl.