Low Ubal concentrations enhance ATP-dependent proteolysis of α-subunits. Each reaction mixture was incubated at 37°C for 2 hours with ³H-α-chains (A through D) or with ³H-α-globin (E through H) as a substrate and with a dialyzed hemolysate from the blood cells of either β-thalassemic donor S.O. (A and E), C.G. (B and F), P.C. (C and G), or S.D. (D and H). ³H-α-chain degradation values obtained in the absence of ATP (2.5%, 2.2%, 1.1%, and 1.7% for mixtures with lysates from S.O., C.G., P.C., and S.D., respectively) or ³H-α-globin degradation values obtained in the absence of ATP (6.9%, 5.3%, 4.7%, and 3.9% for mixtures with lysates from S.O., C.G., P.C., and S.D., respectively) remained essentially constant with the different Ubal concentrations (eg, see Fig 1) and were subtracted from each value obtained in the presence of ATP, an ATP-regenerating system, and supplementary Ub. Data points shown for each Ubal concentration represent ATP-dependent degradation values from duplicate reaction mixtures.