IMMOBILIZED METAL-ION AFFINITY PARTITIONING OF ERYTHROCYTES FROM DIFFERENT SPECIES IN DEXTRAN POLY(ETHYLENE GLYCOL) AQUEOUS-PHASE SYSTEMS

Poly(ethylene glycol) (PEG)-bound ligands partition preferentially int o the top, PEG-rich, phase of dextran (Dx)-PEG aqueous phase systems. The extraction of erythrocytes from beef, dog, horse, human, pig, rabb it, rat and sheep was examined in both non-charge-sensitive and charge -sensitive Dx-PEG phase systems containing PEG-iminodiacetate (IDA) wh ich had been reacted with Cu(II) or Zn(II). PEG-IDA-Cu binds primarily to histidine (His) residues. Phase systems containing excess imidazol e were used to obtain cell partition ratios not attributable to the me tal chelate. In non-charge-sensitive phase systems having lower polyme r concentrations a correlation has been reported between the partition , P, of erythrocytes and their membrane ratio of poly/monounsaturated fatty acids; while in charge-sensitive phases there is some correlatio n between the P values and the cells' relative electrophoretic mobilit ies. At higher polymer concentrations red blood cells accumulate at th e interface and do not partition. Under such conditions addition of th e PEG-IDA-Cu (Zn is less effective) causes erythrocytes to partition i nto the PEG-rich phase in a non-charge-related or charge-associated se quence reminiscent of that found in the absence of chelate in non-char ge-sensitive or charge-sensitive phase systems, respectively, at lower polymer concentrations. PEG-IDA-Cu may thus be useful in extending th e partitioning range of Dx-PEG systems to cells having such low P valu es in non-charge-sensitive and/or charge-sensitive phase systems as to preclude their partitioning even when phase systems are optimized by manipulation of their components. From the cited experiments it would appear that either the His per unit surface area of erythrocytes from different species is about the same causing the non-charge-related or charge-associated surface properties (depending on the phase system us ed) to determine, to a large extent, the P even in the presence of che late or that the non-charge-related or charge-associated surface prope rties outweigh the differences in His content and effect the observed correlations. In contrast to these apparently ''non-specific'' extract ions effected by PEG-IDA-Cu, there are cases in which PEG-IDA-Cu acts as a sensitive probe for recognizing differences in cell surface prope rties not detected by other means.