title: The binding of Yb(III) and Gd(III) to bovin serum albumin by a competitive spectrophotometry.
abstract: A competitive spectrophotometry has been used to study the binding of Yb(III) and Gd(III) to BSA. The indicator ligand, 5-Br-PAPS, as well as its metal complexes, ML, having intense colors with sufficiently separate absorption peaks permits the analysis of the interaction between metal and BSA. Experimental data are analyzed by using Scatchard plots. The results show that both Yb and Gd bind to BSA with four equivalent affinity sites at pH 6-7. Some additional lower affinity sites are observed for Gd but not for Yb. The slope of the plots, the apparent association constant of the metal with BSA, decreases with decreasing pH. The pH dependence of the apparent association constant indicates the 1:1 competition between metal ions and hydrogen ions for the binding site. The intrinsic association constant of the metal, KM(H-1A), and the proton association constant, KH(H-1A) =, are found to be logKM(H-1A) = 7.00 +/- 0.03 and log KH(H-1A) = 7.08 +/- 0.06 for the Yb binding sites, and logKM (H-1A) = 6.16 +/- 0.08 and log KH(H-1A) = 6.63 +/- 0.10 for the Gd binding sites by a graphical analysis (A = BSA).
authors.affiliation: Department of Bioengineering, Yatsushiro National College of Technology, Kumamoto, Japan.
authors.forename: E
authors.initials: E
authors.lastname: Ohyoshi
authors.forename: S
authors.initials: S
authors.lastname: Kohata
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D005682:Gadolinium / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D011522:Protons; D012710:Serum Albumin, Bovine / Q000378:metabolism*; D013053:Spectrophotometry / Q000379:methods*; D015018:Ytterbium / Q000378:metabolism*
chemical_list: D011522:Protons; D012710:Serum Albumin, Bovine; D005682:Gadolinium; D015018:Ytterbium