Cholesterol ester transfer mediated by lipid transfer protein as influenced by changes in the charge characteristics of plasma lipoproteins

The relationship between the cholesterol ester (CE) transfer activity of lipid transfer protein (LTP) and its affinity with lipid and lipoprotein particles was investigated. The study of the effects of chemical modification of low density lipoprotein (LDL) amino groups and carboxyl groups on the CE transfer activity showed that the maximal activity is obtained upon succinylation or acetylation of approximately 7% of LDL amino groups. Further increases in the extent of modification progressively reduced the transfer activity. The treatment of LDL with fatty acids gave results comparable to the chemical modification of LDL amino groups. The addition of low concentrations of fatty acids was stimulatory, while that of high concentrations was inhibitory. Although increases in the positive charges of LDL by the carboxyl group modification did not appreciably influence the CE transfer, the addition of cationic detergents gave a profound effect on the CE transfer. A maximal CE transfer activity was obtained upon addition of very small amounts of the detergents, with the higher concentrations sharply reducing the transfer activity. We also studied the effects of the concentrations of phosphate buffer and various salts on the CE transfer as well as the affinity of LTP for very low density lipoproteins, low density lipoproteins, high density lipoproteins 3, and high density lipoproteins 2. It appeared that the affinity of LTP for various lipoproteins is governed by a delicate balance of electrostatic and hydrophobic interactions. Optimal degrees of the interaction of LTP with both donor and acceptor particles seem to be required for the maximal degree of CE transfer.