In situ activation of human erythrocyte prolidase: potential for enzyme replacement therapy in prolidase deficiency

Deficiency of prolidase is frequently associated with skin lesions and mental retardation. Biochemically, the condition is marked by iminodipeptiduria. We have investigated the feasibility of using donor erythrocytes to replace the deficient enzyme. Prolidase occurs in erythrocytes in an inactive form. If erythrocytes are incubated overnight at 37 degrees C in the presence of 1 mM MnCl2, the intracellular Mn++ concentration increases from 0.014 to 2.04 micrograms/ml. As a consequence, the activity of prolidase in hemolysates increases to 159 mumol glycyl-L-proline hydrolyzed/h/ml compared to 5 mumol/h/ml for hemolysates of cells incubated in the absence of Mn++. Hydrolysis of glycyl-L-proline by intact erythrocytes is reduced by the slow rate of iminodipeptide transport into the cell; however, intact cells hydrolyzed this substrate at a rate 10-20 times faster after preincubation with MnCl2. After exogenous MnCl2 is removed from the storage buffer, high levels of erythrocyte prolidase activity persist for at least 13 days. The kinetic parameters for intact activated erythrocyte-catalyzed hydrolysis of glycyl-L-proline have been estimated. These values predict that donor erythrocytes, activated with Mn++ before transfusion could play a significant role in the recovery of proline from dietary sources of iminodipeptides in patients with prolidase deficiency.