The binding of bivalent metal cations to low-density lipoproteins. An ESR study

The binding of bivalent metal ions Cu2+, Zn2+, Ca2+, Mg2+ to low-density lipoproteins (LDL) was investigated by the ESR technique. The monitoring of ESR spectra of paramagnetic Mn2+ ions in the presence of above-listed cations made it possible to evaluate the dissociation constants of their complexes with LDL. The effective dissociation constant of the complex Mn2+-LDL used for calculations was K-D=(1.1+/-0.4).10(-4) M according to literature data. The investigated cations may be classified into two groups: 1) low dissociation constants were characteristic for Cu2+ ions [K-D= (1.3+/-0.5).10(-4) M] which demonstrated a high oxidative ability, and for Zn2+ [K-D= (0.95+/-0.45).10(-4) M] and Mn2+ ions, which could strongly influence the copper-induced LDL oxidation; 2) Ca2+ and Mg2+ were characterized by higher values of K-D [(6+/-1).10(-4) M and (7.5+/-1.5).10(-4) M, accordingly] and slightly affected the Cu2+-induced oxidation of LDL. The results of the present work reinforced our earlier conjecture that cations may influence the process of lipid peroxidation, binding only to particular binding sites on the surface of LDL.