DETERMINATION OF THE BINDING CONSTANT OF IMIDAZOLE AND HISTIDINE WITH IMMOBILIZED CU(II) BY DIFFERENTIAL UV SPECTROSCOPY

摘要

An iminodiacetic acid derivative of poly(ethylene glycol) (PEG-IDA) with chelated Cu(II) was synthesized. The binding constants between immobilized Cu(II) with imidazole and histidine at various solution pH values, salt concentrations and temperatures were determined by differential UV spectrophotometer, The results indicate that a bimodel binding behavior of basic solute was observed by the study of the salt effect. However, at the pH value higher than pKa of the deprotonation of imidazole nitrogen, the formation of the coordinated compound is the dominate binding mechanism. There is no obvious effect of temperature on binding constants because of the complexity of binding mechanism. The binding behavior of several dipeptides and tripeptides with histidine at C- or N-terminal was also investigated and the results were explained by the ''metal ion transfer'' (MIT) hypothesis. Furthermore, the binding constants of synthetic heptapeptides with two histidine residues separated by different number of glycine residues were investigated to demonstrate the effect of histidine residues distance on the binding affinity. This study provides basic information of binding behavior of protein to immobilized metal ion. [References: 29]