The Characterization and Occurrence of an S 20 Serum Lipoprotein

Abstract In the serum of patients with hyper-pre-β-lipoproteinemia there frequently occurs in abundance an ultracentrifugally distinct low density lipoprotein component of the Sf 20 class. This study concerns the characterization of this component, present in the serum of 14 of 15 patients. The lipoprotein has been isolated ultracentrifugally; it has the electrophoretic and immunological properties of a β-lipoprotein but is distinct from very low density lipoproteins. It has a buoyant density of 1.004 g per ml which is lighter than the major low density lipoproteins of normal serum, and this observation is consistent with its higher triglyceride content. This lipoprotein has a sedimentation coefficient corrected for concentration and viscosity of -68 S, measured in a solvent of density 1.20 g per ml, and a molecular weight of approximately 4.2 million. Electron microscopy of this larger low density lipoprotein shows spherical macromolecules with a diameter approximating 256 A.