Ubiquitin Aldehyde Increases Adenosine Triphosphate-Dependent Proteolysis of Hemoglobin 
-Subunits in 
-Thalassemic Hemolysates
Joseph R. Shaeffer and
Robert E. Cohen
From the Department of Biochemistry, University of Iowa College of Medicine, Iowa City, IA.
Two major causes of the anemia in 
-thalassemia are a deficiency in hemoglobin (Hb) -subunit (and consequently HbA) synthesis and, due to the resulting excess of Hb 
-subunits, erythroid cell hemolysis. The hemolytic component might be ameliorated by increasing the intracellular proteolysis of the excess -subunits. Isolated 3H-labeled -chains are known to be degraded primarily by the adenosine triphosphate (ATP)- and ubiquitin (Ub)-dependent proteolysis pathway in unfractionated -thalassemic hemolysates. Our objective was to increase this degradation by targeted intervention. Ub aldehyde (Ubal), a synthetic inhibitor of isopeptidases (proteases that hydrolyze the bond between the Ub polypeptide and its protein adduct), was added to reaction mixtures containing a hemolysate from the blood cells of one of four -thalassemic donors and 3H--chains or 3H--globin as a substrate. Optimum enhancement of ATP-dependent degradation occurred at 0.4 to 1.5 µmol/L Ubal and ranged from 29% to 115% for 3H--chains and 47% to 96% for 3H--globin among the four hemolysates. We suggest that Ubal stimulates 3H--subunit proteolysis by inhibition of an isopeptidase(s) that deubiquitinates, or "edits," Ub-3H--subunit conjugates, intermediates in the degradative pathway. In control studies, similarly low Ubal concentrations did not enhance the degradation of 3H-22 (HbA) tetramers or inhibit the activities of methemoglobin reductase and four selected glycolysis pathway enzymes. These and other results may be the basis for a therapeutic approach to -thalassemia.
Blood, Vol. 90 No. 3 (August 1), 1997:
pp. 1300-1308
© 1997 by The American Society of Hematology.
