UBIQUITIN ALDEHYDE INCREASES ADENOSINE TRIPHOSPHATE-DEPENDENT PROTEOLYSIS OF HEMOGLOBIN ALPHA-SUBUNITS IN BETA-THALASSEMIC HEMOLYSATES

Two major causes of the anemia in beta-thalassemia are a deficiency in hemoglobin (Hb) beta-subunit (and consequently HbA) synthesis and, du e to the resulting excess of Hb alpha-subunits, erythroid cell hemolys is. The hemolytic component might be ameliorated by increasing the int racellular proteolysis of the excess alpha-subunits. Isolated H-3-labe led alpha-chains are known to be degraded primarily by the adenosine t riphosphate (ATP)- and ubiquitin (Ub)-dependent proteolysis pathway in unfractionated beta-thalassemic hemolysates. Our objective was to inc rease this degradation by targeted intervention, Ub aldehyde (Ubal), a synthetic inhibitor of isopeptidases (proteases that hydrolyze the bo nd between the Ub polypeptide and its protein adduct), was added to re action mixtures containing a hemolysate from the blood cells of one of four beta-thalassemic donors and H-3-alpha-chains or H-3-alpha-globin as a substrate. Optimum enhancement of ATP-dependent degradation occu rred at 0.4 to 1.5 mu mol/L Ubal and ranged from 29% to 115% for H-3-a lpha-chains and 47% to 96% for H-3-alpha-globin among the four hemolys ates, We suggest that Ubal stimulates H-3-alpha-subunit proteolysis by inhibition of an isopeptidase(s) that deubiquitinates, or ''edits,'' Ub-H-3-alpha-subunit conjugates, intermediates in the degradative path way. In control studies, similarly low Ubal concentrations did not enh ance the degradation of H-3-alpha(2) beta(2), (HbA) tetramers or inhib it the activities of methemoglobin reductase and four selected glycoly sis pathway enzymes. These and other results may be the basis for a th erapeutic approach to beta-thalassemia. (C) 1997 by The American Socie ty of Hematology.