Isolation and characterization of simple and complex lipoproteins containing apolipoprotein F from human plasma

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Abstract
The interaction of apolipoprotein F (ApoF) with other apolipoproteins and lipids in human plasma was studied. By the successive use of immunosorbers specific for ApoF, apolipoprotein A-II (ApoA-II) and apolipoprotein A-I (ApoA-I), 3 different ApoF-containing lipoproteins were isolated from normolipidemic fasting human plasma. Their apolipoprotein content was determined by double immunodiffusion against monospecific antisera to all known serum apolipoproteins, electroimmunoassay, crossed immunoelectrophoresis and polyacrylamide gel electrophoresis. Their lipid composition was determined by TLC. The 3 ApoF-containing lipoproteins were identified as LpF:A-I:A-II (lipoprotein containing ApoF, ApoA-I and ApoA:II), LpF:A-I (lipoprotein containing ApoF and ApoA-I) and LpF (lipoprotein containing only ApoF). LpF:A-I:A-II contained ApoF, ApoA-I and ApoA-II in an apparent 2:1:1 molar ratio. Its lipid moiety was characterized by cholesterol ester (45%) and free cholesterol (28%) as the predominant lipids. LpF contained only ApoF, and in its major lipid components there were also cholesterol esters (63%) and free cholesterol (21%). ApoF-containing lipoproteins may be involved in transport and/or esterification of cholesterol.