A comparison of nonhuman primate plasma lipoproteins isolated by swinging bucket rotor density gradient or fixed angle rotor differential ultracentrifugation is described. Whereas these two methods produced comparable results for the composition of low density (LDL) and high density (HDL) lipoproteins, the very low density lipoprotein (VLDL) fraction isolated with the swinging-bucket rotor contained relatively more cholesterol (free and esterifred) and less phospholipid and protein than that fraction obtained with the fixed-angle rotor. Estimations of lipoprotein concentration by agarose gel electrophoresis and particle size by electron microscopy coupled with molar ratios of surface to core constituents indicated that the swinging bucket procedure resulted in a more complete harvest of VLDL particles, especially those in the larger size range.
Plasma lipoproteins have been conventionally
separated in fixed angle rotors by differential ultracentrifugation into very low density (VLDL), low density (LDL), and high density (HDL) lipoproteins. Typically, lipoproteins from as many as 18 plasma samples which have been adjusted to the appropriate solvent density for each lipoprotein class can be isolated by multiple centrifugations in 76 hr with the fixed angle rotor, such as a 40.3 rotor. Necessary precautions in the isolating procedures are the gentle overlaying of the d = 1.006 g/cm3 density solution for the VLDL spin and effecting complete transfer of the gelatinous bottom material rich in lipoproteins following each centrifugation.
Since the infranatant and density solutions are mixed prior to centrifugation of LDL and HDL, there is no concern about sample disturbance. Disadvantages associated with fixed angle differential centrifugation include the numerous sample collections and transfers, convective disturbances arising during centrifugation (1,2), and contamination of lipoproteins with other serum proteins (2). Several investigators have described the separation of lipoproteins by density gradient ultracentrifugation employing swinging bucket rotors (2-6). This procedure minimizes many of the problems described above for