Surface localization of apolipoprotein AII in lipoprotein-complexes.

Lipoprotein particles reconstituted from the apolipoprotein AII (apo AII) component of human serum high density lipoprotein, phosphatidylcholine and lysophosphatidylcholine were covalently linked to the imidoester groups of a polystyrene residue. Apo AII was proteolytically digested with thermolysin after delipidation. The covalently bound peptides remaining at the resin were cleaved and separated by combined two-dimensional electrophoresis/chromatography. The peptides were isolated, hydrolyzed and their amino acid composition determined. They were assigned to the apo AII sequence. Since the imidoester groups on the surface of the resin carrier cannot react with buried lysine residues, this method gives strong chemical evidence for the spreading of the apo AII polypeptide chain over the surface of the lipoprotein particle, as far as the sequence carrying lysine residues between residue 22 and 55 of each symmetrical half is concerned.