In this report, we describe the interaction of human lipid transfer protein with various lipoproteins and the effects of apoproteins on the lipid transfer protein reaction.
1) To determine the binding of LTP with isolated lipoproteins, lipoprotein-coupled Sepharose 4B column was used. From the elution profiles of the column, LTP bound to HDL but hardly bound to LDL in the condition of ionic strength 0.16 NaCl-phophate buffer (pH 7.4) at 4°C. The bound LTP was easily dissociated by changing the buffer to low ionic strength medium. The binding capacity of LDL was increased by applying LTP at higher pH or by acylation of the amino group of LDL. These data indicate that both ionic interaction and hydrophobic interaction participate in the binding of LTP with lipoproteins.
2) To evaluate the effects of apoproteins in the lipid transfer process, we used purified human LTP prepared with our new method and the assay system of proteoliposomes (or liposomes) to LDL. Apo A-I had not only stabilizing effect but also enhancing effect on LTP reaction. Apo A-II or apo E alone had no significant effect on LTP but had some activating effect in the presence of apo A-I. On the other hand, apo D showed some inhibitory effect on LTP reaction.
These data suggest that the lipid transfer reaction in the plasma is regulated by various modification of lipoproteins and the level of apoproteins.
