Improved metabolic properties of hexokinase-overloaded human erythrocytes

Human erythrocytes were loaded with homogeneous hexokinase purified from human placenta (an enzyme species apparently identical to the erythrocyte enzyme), using a procedure of encapsulation based on hypotonic hemolysis, isotonic resealing and reannealing. The hexokinase-overloaded erythrocytes contained 4.77 +/- 0.75 IU of hexokinase activity per ml of packed erythrocytes, a value 15-times higher than that of corresponding unloaded or native red cells. The hexokinase-loaded erythrocytes were found to metabolize twice the amount of glucose consumed by the unloaded cells through a nearly doubled glycolytic activity, while the activity of the hexose monophosphate shunt pathway was unmodified. Estimates of glycolytic intermediates showed increased levels of most metabolites with respect to the unloaded erythrocytes, while the intracellular concentrations of adenine nucleotides and 2,3-bisphosphoglycerate were unaffected by entrapment of hexokinase. The new steady-state condition characterized by improved glycolytic function was demonstrated to be directly related to enhanced levels of hexokinase activity and not to the use of a rejuvenation solution during the procedure of entrapment. These results are consistent with suggestions by several investigators that glucose metabolism in human erythrocytes is regulated by hexokinase, and they open new perspectives for manipulating erythrocytes with the ultimate aim of improving their survival under different storage conditions.