Effect of Common Buffers and Heterocyclic Ligands on the Binding of Cu(II) at the Multimetal Binding Site in Human Serum Albumin

Table 1

Quantitative description of ternary complexes formed by Cu(II) ions at MBS of HSA at pH 7.4. Standard deviations of significant values of experimental logarithms constants on the last digits are given in parentheses.

Ligand (L)	log 𝐾app	log 𝐾111^a	log 𝐾11^b	log 𝐾e^c	log 𝐾T^d	CI^e
[L] =						0.5 mM	100 mM
NaCl	4.60(3)					7.62
Hepes	4.45(5)	7.54(5)	3.22	4.32	−0.28	7.71	9.27
Tris	4.23(6)	8.22(5)	4.05	4.17	−0.43	7.74	9.42
Phosphate	5.17(7)	8.2(1)	3.20	5.00	+0.40	8.04	10.13

^a𝐾₁₁₁ is the equilibrium constant of the reaction Cu²⁺+L+MBS = Cu(MBS)(L).
^b𝐾₁₁ is the equilibrium constant of the reaction Cu²⁺+L = Cu(L); literature values [30–32].
^c𝐾_e is the equilibrium constant of the reaction MBS + Cu(L) = Cu(MBS)(L); log 𝐾₁₁₁ = log 𝐾₁₁ + log 𝐾_e.
^d𝐾_T is the equilibrium constant of the reaction Cu(MBS) + Cu(L) = Cu(MBS)(L) + Cu²⁺.
log 𝐾_T=log𝐾₁₁₁−log𝐾₁₁−log𝐾_app (NaCl).
eCI is the competitivity index (description in text), calculated for following total concentrations: Cu(II) and Z = 1 𝜇M, HSA = 0.5 mM, buffer = 0.5 mM, or 100 mM.