Protection of erythrocyte membrane amino groups from reaction with methyl acetimidate by pyridoxal 5'-phosphate Schiff base formation.
Pre-equilibration of erythrocytes with the membrane-impermeable aldehyde, pyridoxal 5'-phosphate, for 30 min at 22 degrees C, prior to the addition of methyl acetimidate to the incubation mixture has been shown to prevent agglutination of acetamidinated cells which were resuspended in immune serum (Chao, T.L. and Berenfeld, M.R. (1981) J. Biol. Chem. 256, 5324-5326). This observation led to the possibility that the immune reaction, observed in some sickle cell anemia patients to reinfused cells which had been reacted with methyl acetimidate, could be prevented. The present communication further evaluates that reaction sequence and shows that while the pre-equilibration of cells with pyridoxal 5'-phosphate does protect membrane amines from reaction with methyl acetimidate, the protection is not extensive enough to prevent an immune response in a sickle cell anemia patient who had already been sensitized against acetamidinated cells. It is apparent that the design of antisickling agents which covalently modify hemoglobin must take into account protection of functional groups in the erythrocyte membrane, modification of which could produce an immunogenic response.