Studies on the interaction of heparin with serum lipoproteins in the presence of Ca2+, Mg2+, and Mn2+

The interaction between human serum lipoproteins and heparin in the presence of Ca2+, Mg2+, and Mn2+ was studied; HDL2 formed four times more insoluble complexes than HDL3 and LDL showed specificity for interacting with only LDL and VLDL.

Abstract

The interaction between human serum lipoproteins and heparin in the presence of Ca2+, Mg2+, and Mn2+ was studied. Heparin coupled to 1,4-diaminobutane Sepharose 4B derivative was equilibrated with very low density (VLDL), low density (LDL), and high density (HDL) lipoproteins at pH 7.4 in the presence of various concentrations of metal ions. With LDL and VLDL the interaction is quantitative only within a narrow range of metal ion concentration (0.02–0.04 m). The reversibility of the reaction above the critical metal ion concentration was 100, 60, and 10% for Ca2+, Mg2+, and Mn2+, respectively. The relative stability of the LDL-heparin complexes with increasing ionic strength was of the order Mn2+ > Mg2+ > Ca2+, Ca2+ and Mg2+ showed specificity for interacting with only LDL and VLDL. In contrast, HDL formed complexes with heparin in the presence of Mn2+; HDL2 formed four times more insoluble complexes than HDL3. Studies with acetylated LDL and LDL treated with phospholipase C indicated the involvement of LDL negative charges in forming insoluble complexes in the presence of Ca2+.