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The conditional stability constant at pH 7.4 for Cu(II) binding at the N-terminal site (NTS) of human serum albumin (HSA) was determined directly by competitive UV-vis spectroscopy titrations using nitrilotriacetic acid (NTA) as the competitor in 100 mM NaCl and 100 mM N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid (Hepes). The log Kc (NTS) value of 12.0 +/- 0.1 was determined for HSA dissolved in 100 mM NaCl. A false log log Kc (NTS) (c) value of 11.4 +/- 0.1 was obtained in the 100 mM Hepes buffer, owing to the formation of a ternary Cu(NTA)(Hepes) complex. The impact of the picomolar affinity of HSA for Cu(II) on the availability of these ions in neurodegenerative disorders is briefly discussed.

A comparative study of thermodynamic and kinetic aspects of Cu(II) and Ni(II) binding at the N-terminal binding site of human and bovine serum albumins (HSA and BSA, respectively) and short peptide analogues was performed using potentiometry and spectroscopic techniques. It was found that while qualitative aspects of interaction (spectra and structures of complexes, order of reactions) could be reproduced, the quantitative parameters (stability and rate constants) could not. The N-terminal site in HSA is much more similar to BSA than to short peptides reproducing the HSA sequence. A very strong influence of phosphate ions on the kinetics of Ni(II) interaction was found. This study demonstrates the limitations of short peptide modelling of Cu(II) and Ni(II) transport by albumins.

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