Ubal enhances degradation of ³H-α-chains, but not of tetrameric ³H-HbA reconstituted from them. Each reaction mixture was incubated at 37°C for 2 hours with a dialyzed hemolysate from the blood cells of a β-thalassemic donor (P.C.) and with either the usual concentration (0.15 μg/μL) of ³H-α-chains or an equivalent concentration of ³H-α-chains in HbA (³H-α₂β₂-tetramer) as a proteolysis substrate. Values from mixtures with ATP, an ATP-regenerating system, and supplementary Ub are plotted for the degradation of free ³H-α-chains (▴) or ³H-α₂β₂ (▪). Unfilled symbols represent degradation values of the corresponding ³H-protein from otherwise duplicate mixtures without ATP. The substrates were prepared from protein stocks, each 5.0 mg/mL in a 10-mmol/L PO₄ (K⁺), pH 7.0, buffer, by the addition of 20 μL ³H-α-chains to either 25 μL buffer alone or 25 μL nonradioactive human Hb β-chains²⁹; these mixtures were incubated at 4°C for 2 hours to provide free ³H-α-chains or ³H-α₂β₂-tetramers, respectively.