The Metabolic Role of Glucose 1,6-P2 in Human Erythrocytes Studied by Encapsulation Procedures

Red blood cells (RBC) possess many desirable properties of a suitable carrier of exogenous agents to modify the plasma environment or to be organ targeted within the reticuloendothelial system.1-4 Among the agents that can be encapsulated are: enzymes to correct inborn errors of metabolisms5, antineoplastic molecules in cancer6, chelators for transfusion iron overload.7,8 A different, non therapeutic, application of loaded RBC can be that of studying the metabolism of a certain substance transferred inside the cell or to observe its effect on the normal cellular metabolism. In this second view, we have applied the encapsulation procedures based on hypotonic hemolysis, isotonic resealing and reannealing, described by Ropars et al.9, to overloaded human RBC with glucose 1,6bisphosphate (G1c1,6P2) in order to investigate the metabolic role of the phosphorylated sugar in the whole cell. This study is of interest since Glc1,6P2 in RBC, besides being the coenzyme of phosphoglucomutase, appears to affect the three key enzymes of glycolysis, namely it inhibits hexokinase, and activates phosphofructokinase and pyruvate kinase.10 Intracellular Glc1,6P2 concentration has been increased by loading human RBC with the commercial product or with the enzyme Glc1,6P2- synthase purified from rabbit skeletal muscle11. In both experimental conditions the augmentation of the Glc1,6P2 cellular level is accompanied by a reduced glucose utilization. The significance of the results, with reference to the site(s) of glucose metabolism regulation by the bisphosphate, is discussed.