Structural and Compositional Changes Attending the Ultracentrifugation of Very Low Density Lipoproteins

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Abstract
The effects of repetitive ultracentrifugation on the physical and chemical properties of very low density lipoproteins (VLDL) were investigated. VLDL recentrifuged one to seven times were characterized by chemical analyses, analytical ultracentrifugation and electron microscopy. The VLDL content of triglyceride was increased and the proportion of phospholipid decreased by ultracentrifugation. Recentrifugation of VLDL decreased the number of Sf o 20–100 particles and generated particles of Sf o > 400. The bulk of the material removed from VLDL by ultracentrifugation was lipoprotein having pre-g mobility on paper electrophoresis, flotation rates of Sf o 10–100 and a particle size of 300–400 Å. Two ultracentrifugations separated an average of 14% of the starting VLDL protein. Characterization of the apoproteins in this material by polyacrylamide gel electrophoresis, gel chromatography, immuno precipitation and amino acid analysis demonstrated a relatively high proportion of B-apoprotein and relatively little C-apoproteins.