Purification of immunoglobulin G from human plasma by metal-chelate affinity chromatography

A new group of specific-affinity beads with metal chelates as ligands and synthetic polymer beads as support matrices was prepared and tested. This study focused on developing metal-chelated poly(hydroxyethyl methacrylate) (PHEMA) gel beads in a spherical form (100150 μm in diameter) for the separation of immunoglobulin G (IgG) from human plasma. Crosslinked PHEMA gel beads were prepared by suspension polymerization. The metal-complexing ligand L-histidine was then immobilized by covalent binding onto these gel beads. Different transition-metal ions, including Zn(II), Ni(II), Co(II), and Cu(II), were chelated on these gel beads. An elemental analysis of immobilized L-histidine for nitrogen was estimated to be 401.9 μmol of L-histidine/g of PHEMA. The nonspecific IgG adsorption onto plain PHEMA gel beads was negligible (ca. 0.17 mg/g). Higher adsorption values (up to 3.5 mg/g) were obtained in which L-histidine-iminobilized PHEMA gel beads were used from aqueous solutions. A remarkable increase in the IgG adsorption capacities were achieved from human plasma with L-histidine-immobilized gel beads (up to 44.8 mg/g). Further increases in the IgG adsorption capacities of the metal-chelated gel beads were observed when human plasma was used (up to 79.6 mg/g). The metal-chelate affinity gel beads allowed the one-step separation of IgG from human plasma. The recognition range of metal ions for surface histidines from human plasma followed this order: Cu(II) > Ni(II) > Zn(II) > Co(II). IgG molecules could repeatedly be adsorbed and desorbed with these metal-chelated PHEMA gel beads without a noticeable loss in their IgG adsorption capacity.