Coordination ability of the 29-amminoacid residue squash trypsine inhibitor and two of its analogues towards Cu(II) ions

Successful application of the potentiometric method together with NMR, EPR, CD and absorption spectroscopy yielded accurate data concerning the stabilities of the complexes formed and their binding modes between Cu-II and squash trypsin inhibitor. The major residue involved in the metal ion co-ordination is the His-25 imidazole side chain, which acts as an anchoring donor and is bound to metal ion over the whole pH range (3-11.5) studied. The 3N complex with {N-imid, N-His25(-), N-Glu24(-)} binding mode dominates at physiological pH. The data obtained indicate that the protein after a particular mutation could be useful to model metal centres of large proteins.