title: Adsorption of Mn(II) ions to human low density lipoproteins. Magnetic resonance studies.
abstract: Mn(II) ions were used to study ion-binding properties of human low density lipoproteins (LDL). From the intensity of the EPR lines corresponding to the unbound Mn(II) ions the percentage of the ions bound to LDL is determined. By the titration of LDL with Mn(II) the binding parameters, dissociation constant, Kd, and the number of binding sites, n, could be derived. It has been found that there are at least two types of binding site on the LDL surface: 'strong' sites characterized by n = 6, Kd =1 x 5 x 10(-5)M x 1(-1), and 'weak' sites characterized by n = 145 and Kd = 6.6 x 10(-3)M x l(-1) for the sample in 0.01 M Tris-HCl buffer at 10 degrees C. At very low Mn(II) concentrations binding to the 'strong' sites exhibits a cooperative behaviour. In the 0.1 M buffer the 'strong' sites are almost completely occupied or blocked by the monovalent buffer cations. The number of the 'weak' sites remains unaltered and Kd is decreased slightly (Kd = 4.9 x 10(-3)M x (-1)). The location, chemical nature and the structural and functional relevance of the binding sites are discussed.
mesh_terms: D001665:Binding Sites; D006801:Humans; D007700:Kinetics; D008077:Lipoproteins, LDL / Q000097:blood*; D009682:Magnetic Resonance Spectroscopy; D008345:Manganese; D011485:Protein Binding; D013696:Temperature
chemical_list: D008077:Lipoproteins, LDL; D008345:Manganese