Immobilization of a protein through coordinate bonds formed with divalent metal ions (e.g., Me(II), Cu(II)) is becoming an attractive alternative to covalent coupling chemistries. This is primarily a result of the reversible nature of the immobilization, because the protein may be easily removed from the support matrix through interruption of the protein-metal bond. The primary requirement for immobilization via Me(II) interaction is surface histidine residues (1 –4 ), When such residues are absent, genetic engineering may be used to enhance metal affinity by incorporation of histidine containing metal affinity tails (5 –8 ). Thus proteins of varying sources and enzymatic activity may be immobilized using this technique (9 ,10 ).
