Spectroscopic and thermodynamic determination of three distinct binding sites for Co(II) ions in human serum albumin

Journal of Inorganic Biochemistry
Volume 103, Issue 7, July 2009, Pages 1005-1013

Human serum albumin (HSA) is the most abundant protein of blood serum, involved in the transport of metal ions, including Co(II). Using circular dichroism spectroscopic titrations we characterized three distinct Co(II) binding sites in HSA. Applying Cu(II), Ni(II) and Cd(II) ions as competitors we determined that these sites are identical with three binding sites known for other metal ions. We ordered these sites according to their binding affinities as cadmium site B (CdB) > multi-metal binding site (MBS) > N-terminal binding site (NTS).

Using isothermal titration calorimetry (ITC) we confirmed the presence of these three binding sites and determined their conditional binding constants at pH 7.4 as 9 ± 5, 1.1 ± 0.5, and 0.9 ± 0.3 × 104 M−1, respectively. The impact of these results on the albumin cobalt binding (ACB) clinical assay for myocardial ischemia is discussed.

Magdalena Sokołowskaa, Małgorzata Wszelaka-Rylikb, Jarosław Poznańskib, c and Wojciech Balc, d, ,
aDepartment of Hygiene, Wroclaw Medical University, Mikulicza-Radeckiego 7, 50-368 Wroclaw, Poland
bInstitute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
cInstitute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawińskiego 5a, 02-106 Warsaw, Poland
dCentral Institute for Labour Protection – National Research Institute, Czerniakowska 16, 00-701 Warsaw, Poland