Fractionation of chylomicrons by heparin-sepharose chromatography. Characterization of two heparin-binding proteins.
Rat lymph chylomicrons were separated into two fractions using heparin-Sepharose chromatography: a major fraction which elutes from the column with the void volume at 0.05 M NaCl, and a smaller fraction which binds to the column at 0.05 M NaCl and elutes at 0.3 M NaCl. These two fractions differ in mean particle size, and lipid and protein compositions. Both fractions share apolipoproteins B, A-IV, E, A-I, and C, but the fraction which binds to heparin-Sepharose contains two additional proteins: protein I (Mr = 6.0 X 10(4)), and protein II (Mr = 8.0 X 10(4)). Both proteins are also present in the lipoprotein-free fraction of rat serum. Proteins I and II bind to heparin-Sepharose, and are highly amphiphilic: they bind with high affinity to phospholipid surfaces and form stable monolayers at the air-water interface. The molecular weight, amino acid composition, heparin binding, and amphiphilicity of protein I resemble that of beta 2-glycoprotein I; in addition, protein I from rat lymph chylomicrons cross-reacts with rabbit antiserum to human beta 2-glycoprotein I, suggesting that these two proteins are homologous. Protein II appears to be a previously undescribed protein. The possible functions of these two proteins are discussed.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001053:Apolipoproteins / Q000032:analysis / Q000378:metabolism; D002914:Chylomicrons / Q000302:isolation & purification* / Q000378:metabolism; D006023:Glycoproteins / Q000302:isolation & purification / Q000378:metabolism; D006493:Heparin / Q000378:metabolism*; D005779:Immunodiffusion; D008055:Lipids / Q000032:analysis; D008196:Lymph / Q000032:analysis*; D008297:Male; D008970:Molecular Weight; D011506:Proteins / Q000302:isolation & purification* / Q000378:metabolism; D051381:Rats; D053482:beta 2-Glycoprotein I
D000596:Amino Acids; D001053:Apolipoproteins; D002914:Chylomicrons; D006023:Glycoproteins; D008055:Lipids; D011506:Proteins; D053482:beta 2-Glycoprotein I; D006493:Heparin