The isolation and characterization of high-density-lipoprotein subfractions containing apolipoprotein E from human plasma.

1. Plasma high-density lipoprotein (HDL) was separated by heparin-Sepharose affinity chromatography into a non-bound, apolipoprotein E-poor, and a bound, apolipoprotein E-rich, fraction through the binding effect of Mn2+ in the column buffer. 2. The application of a series of elution buffers in which the concentration of Mn2+ was progressively replaced by Mg2+ resulted in the separation of the bound HDL into five subfractions. 3. Each subfraction migrated a different distance on gradient-gel electrophoresis. Three of the subfractions had RF (relative migration compared with BSA) values within the range of HDL2b. One subfraction contained largely HDL2a, with some material in the regions of HDL2b and HDL3a, and one subfraction spanned the RF regions of HDL2a, HDL3a and HDL3b. 4. The number of molecules, per HDL particle, of cholesteryl ester, non-esterified cholesterol and phospholipid increased with particle size, whereas triacylglycerol passed through a maximum and the number of amino acid residues remained approximately the same. 5. Apolipoprotein (apo) A-I was the major apoprotein in all five subfractions, but the latter differed appreciably in their contents of apo A-II and apo E. 6. The major fatty acid component of each subfraction was linoleic acid, with moderate amounts of C16:0 and C18:1 fatty acids and a smaller content of C18:0, C20:4,n-6 and C22:6,n-3, with no significant difference in composition between the subfractions. 7. This paper provides the first description of a method for the isolation of three subfractions of HDL2b together with other subfractions in quantities that are sufficient for further analytical or metabolic studies.