Co-ordination ability towards Cu-II of the 29-amino acid residue trypsin inhibitor of squash and two of its analogues

Successful application of the potentiometric method together with NMR, EPR, CD and absorption spectroscopy yielded accurate data concerning the stabil ities of the complexes formed and their binding modes between Cu-II and squ ash trypsin inhibitor. The major residue involved in the metal ion co-ordin ation 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 phy siological pH. The data obtained indicate that the protein after a particul ar mutation could be useful to model metal centres of large proteins.