The mechanism of recognition and interactions of LDL (low density lipoprotein) with different charged ligands on adsorbents was studied. Tryptophan, lysine residues and carboxyl terminus on LDL were chemically modified by pyridoxal 5-phosphate (PP), N-Ethyl-N'[3-(dimethylamino)propyl]carbodiimide (EDC) and N-bromosuccinimide (NBS), respectively. Due to the effectiveness of L-lysine in the removal of LDL-C (LDL-cholesterol), it was selected to study the interaction of ligand with the modified LDL. Experimental results show that positive charge on the surface of LDL interacts with the negative charged carboxyl groups Of L-lysine by electrostatic force, thus resulting in the adsorption of LDL by the, absorbent. We also found that increasing the positive charge on the surface of LDL could enhance the adsorption capacity of the adsorbent. On the contrary, increasing the negative charge could decrease the adsorption ability. Thus, different adsorbents containing sulfonic groups, phosphoric groups, L-lysine and carboxyl groups as the ligand were synthesized for investigating the effect of electric charge on their adsorption capacity. Results show that the adsorption capacity increases with the increase of the electronegativity of the ligand on the adsorbent. (c) 2007 Elsevier Ltd. All rights reserved.