, Volume 11, Issue 6, pp 645-652

Binding of benzo(α)pyrene, ellipticine, and cis-parinaric acid to β-lactoglobulin: Influence of protein modifications

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Abstract

The binding of benzo(α)pyrene, ellipticine, and cis-parinaric acid to native, esterified, and alkylated β-lactoglobulin was followed by enhancement of the ligand fluorescence. Three studied ligands bind to native or modified β-lactoglobulin in apparent molar ratios varying between 1/8 and 2/1, with apparent dissociation constants in the range of 10−8 M for ligand/β-lactoglobulin complexes. The studied, chemically modified β-lactoglobulin derivatives display higher binding affinities for all studied ligands, cis-parinaric acid excluded. The reductive alkylation of ε-NH2 lysyl residues of β-lactoglobulin increases the apparent molar ratios of benzo(α)pyrene and cis-parinaric acid, and decreases it for ellipticine. The esterified and native β-lactoglobulin complexed to the investigated ligands display similar stoichiometries. Dynamic light scattering study of ligand-β-lactoglobulin complexes in solution shows the formation of aggregates: the apparent hydrodynamic radius value of β-lactoglobulin dimer (3.4 nm) reaches 49, 46, and 74 nm upon addition and binding of benzo(α)pyrene, ellipticine, and cis-parinaric acid, respectively.