Isolation and lipid-binding properties of rat apolipoprotein A-IV.
Apolipoprotein A-IV was isolated from the d less than 1.21 g/ml fraction of rat serum by gel filtration followed by heparin-Sepharose affinity chromatography; this method also facilitated the preparation of apolipoprotein A-I and apolipoprotein E. The apolipoprotein A-IV preparation was characterized by SDS-gel electrophoresis, isoelectric focusing, amino acid analysis and immunodiffusion. The lipid-binding properties of this protein were studied. Apolipoprotein A-IV associated with dimyristoylphosphatidylcholine (DMPC) to form recombinants which contained two molecules of apolipoprotein A-IV and had a lipid/protein molar ratio of 110. The density of the DMPC/apolipoprotein A-IV particles was determined to be 1.08 g/ml and the particles were visualized by electron microscopy as discs which were 5.8 nm thick and 18.0 nm in diameter. The stability of the DMPC/apolipoprotein A-IV recombinants, as determined by resistance to denaturation, was comparable to the stability of DMPC/apolipoprotein A-I complexes. However, by competition studies it was found that apolipoprotein A-I competed for the binding to DMPC more effectively than did apolipoprotein A-IV. It is concluded that, while rat apolipoprotein A-IV resembles other apolipoproteins in its lipid-binding characteristics, it may be displaced from lipid complexes by apolipoprotein A-I.
D000596:Amino Acids / Q000097:blood; D000818:Animals; D016632:Apolipoprotein A-I; D001054:Apolipoproteins A / Q000097:blood / Q000378:metabolism*; D001667:Binding, Competitive; D002499:Centrifugation, Density Gradient; D002850:Chromatography, Gel; D002942:Circular Dichroism; D004586:Electrophoresis; D006493:Heparin; D005779:Immunodiffusion; D007525:Isoelectric Focusing; D050356:Lipid Metabolism; D011485:Protein Binding; D051381:Rats
D000596:Amino Acids; D016632:Apolipoprotein A-I; D001054:Apolipoproteins A; C022205:apolipoprotein A-IV; D006493:Heparin