SDS-PAGE of purified β-globin variants. β-chain variants (2 to 5 μg) expressed in bacteria were purified and subjected to SDS-PAGE after treatment with (+) or without (-) 200 mmol/L DTT for 30 minutes at 25°C. After heating for 3 minutes in the presence of 3% (wt/vol) SDS in a boiling water bath, samples were electrophoresed on a 12.5% (wt/vol) polyacrylamide gel at a constant voltage of 100 V. Gels were stained with Coomassie Brilliant Blue R-250 to detect proteins. (A) Molecular weight standards (Amersham Life Science, Arlington Heights, IL); (B) β16 Gly→Asp chain; (C) β95 Lys→Glu chain; (D) β120 Lys→Glu chain; (E) β16 Gly→Asp, 120 Lys→Glu chain; (F) β112 Cys→Asp chain; and (G) β^▵ chain.