APOPROTEIN-PHOSPHOLIPID INTERACTIONS IN LP(A)

Lipoprotein (a) (Lp(a)) and low-density lipoprotein (LDL) are structur ally related to each other. Both exhibit identical phospholipid compos itions and possess one molecule of apoprotein B-100 (apoB). Lp(a) cont ains, in addition, apoprotein (a) (apo(a)), which localizes to the par ticle surface and interacts with the apoB component by non-covalent an d covalent forces. Protein-protein interaction is probably interrelate d with protein-lipid interaction. Fluorescent analogs of phosphatidylc holine and sphingomyelin were inserted into the surface layer of LDL a nd Lp(a). The obtained fluorescence data reflecting mobility and distr ibutional heterogeneity of the labeled lipids provided evidence that a poproteins discriminate between choline phospholipids and preferential ly associate with phosphatidylcholine. This effect is enhanced in Lp(a ) because of the presence of apolipoprotein (a). Higher affinity for L p(a) as compared with LDL was also observed with a fluorescent diether analog of phosphatidylcholine in native serum. in contrast, the time- dependent transfer of the same lipid into Lp(a) was slower compared wi th LDL, probably as a consequence of the more rigid surface of the for mer lipoprotein.