Isothermal titration calorimetry measurements of Ni(II) and Cu(II) bindingto His, GlyGlyHis, HisGlyHis, and bovine serum albumin: A critical evaluation
Y. Zhang et al., Isothermal titration calorimetry measurements of Ni(II) and Cu(II) bindingto His, GlyGlyHis, HisGlyHis, and bovine serum albumin: A critical evaluation, INORG CHEM, 39(14), 2000, pp. 3057-3064
The binding of Ni(II) and Cu(II) to histidine, to the tripeptides GlyGlyHis
and HisGlyHis, and to the protein bovine serum albumin has been studied by
isothermal titration calorimetry (ITC) to determine the experimental condi
tions and data analysis necessary to reproduce literature values for the bi
nding constants and thermodynamic parameters. From analysis of the ITC data
, we find that there are two major considerations for the use of this metho
d to accurately quantify metal ion interaction with biological macromolecul
es. First, to determine true pH-independent binding constants, ITC data mus
t be corrected for metal ion competition with protons by accounting for the
experimental pH and pK(a) values of the metal-binding residues. Second, me
tal interaction with the buffer (stability and enthalpy of formation of met
al-buffer complex(es)) must be included in the analysis of the ITC data to
determine the binding constants and the change in enthalpy. While it may be
possible to use a buffer that forms only weak, and therefore negligible, c
omplexes with the metal, a buffer that has a strong and well-characterized
interaction has the benefit of suppressing metal ion hydrolysis and precipi
tation, and of allowing the quantification of high-affinity metal-binding s
ites on biological macromolecules. This study has also quantified the contr
ibution of the N-terminal imidazole of HisGlyHis to the stability of the Cu
(II) and Ni(II) complexes of this protein sequence and has provided new ins
ight about Cu(II) binding to albumin.