Each reaction mixture was prepared with a dialyzed hemolysate from the blood cells of 1 of 4 β-thalassemic donors, ³H-α-chains as substrate, ATP, and an ATP-regenerating system with or without the usual concentration (47 μmol/L) of supplementary Ub. Replicate mixtures contained 0 to 1.0 μmol/L Ubal and were incubated at 37°C for 2 hours. Curves of ATP-dependent proteolysis similar to those shown in Fig 2 were plotted after subtraction of ATP-independent degradation values of 2.1%, 2.5%, 1.3%, and 1.8% obtained with the lysates from S.O., C.G., P.C., and S.D., respectively. Values for ATP-dependent proteolysis (% TCA-soluble radioactivity) of ³H-α-chains from mixtures without Ubal and from those with a Ubal concentration (0.6 to 0.8 μmol/L) resulting in maximum stimulation of degradation together with the corresponding calculated % increase are presented.