The plasma apoliproteins (apoLP) are major determinants of the fate of the lipoprotein (LP) particles on which they reside. This project focuses on one particular apoLP, apo E, which has been shown to be an important determinant of LP/cell interaction. Preliminary data from our laboratory have shown that column chromatography of whole plasma on 4% agarose separates the major classes of the plasma LP effectively without the artifactual changes introduced by ultracentrifugation. Within this spectrum, we have specifically identified three apo E containing LP subfractions. The first of these (subfraction 1) actually comprises two populations of apo E containing particles which are indistinguishable in size from the triglyceride-rich LP, chylomicrons (fraction Ic) and very low density LP (fraction Iv). The other two apo E containing subfractions (fractions II and III, ) however, are discrete LP particles which are larger than low density LP (LDL) and larger than high density LP (HDL,) respectively. The proposed studies will focus initially on physical and chemical characterization of these subfractions using molecular sieve and immunoaffinity chromatography in sequence. In preliminary studies, we have already demonstrated the ability to separate intact particles containing apo E in association with other apoLP and lipids by immunoaffinity chromatography using ant./apo E IgG Sepharose. Subsequent studies will take advantage of wjis method of selectibely isolating specific apo E containing LP subfractions, in order to completely characterize their apoLP and lipid composition and to investigate their metabolic origins and interrelationships. We propose that these discrete subfractions exist as result of definable metabolic processes possibly involving the lipolytic enzymes lipoprotein lipase (LPL) and hepatic triglyceride lipose (HTGL). Studies involving in vitro, cell bound, and in vivo lipases will be combined with clinical and kinetic studies in order to test specific hypotheses relating to the origin of apo E containing LP subfractions.
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