Apolipoprotein A-l-containing lipoproteins with pre-beta electrophoretic mobility

Among the apoA-I-containing lipoproteins isolated by selected-affinity immunosorption from human serum and plasma, we have identified a subpopulation which, unlike the bulk of high density lipoproteins, has pre-beta electrophoretic mobility. This pre-beta subpopulation can be observed directly in fresh plasma by immunoelectrophoresis. It contains phospholipid and free and esterified cholesterol, but protein constitutes 90% of its mass. Apolipoprotein A-I is the predominant apolipoprotein in this subpopulation; apolipoprotein A-I1 and the B lipoproteins are not detected. The protein moiety of this subpopulation exhibits markedly lower helicity than that of high density lipoproteins isolated by ultracentrifugation. -Kunitake, S. T., K. J. La Sala, and J. P. Kane. Apolipoprotein A-I-containing lipoproteins with pre-beta electrophoretic mobility. J. Lipid Res. 1985. 26: 549-555. Supplementary key w o r d s HDL subspecies The high density lipoproteins (HDL) are a set of particles which are both structurally and functionally heterogeneous, differing with respect to particle size, composition, and biological activity. This heterogeneity has been demonstrated by a number of different strategies of subfractionation (1-5). Sequential ultracentrifugal flotation of HDL, often used as the primary method or as an early step in the separation of subfractions of HDL, allows gross observation of HDL heterogeneity but cannot yield individual subspecies. This technique appears to perturb lipoproteins, at least in that apolipoproteins are lost from the lipoprotein complexes (6-10). Also, ultracentrifugation does not isolate apolipoprotein (apo) A-I-containing lipoproteins that fall outside the density range of 1.063 < d < 1.21 g/ml. For the first step in isolation of HDL subspecies, we have developed a new technical strategy, selected-affinity immunosorption (11, 12), which permits the quantitative isolation of apoA-I-containing lipoproteins with minimal perturbation. A recent study by Cheung and Albers (13) has confirmed the suitability of this technique for isolating apoA-I-containing lipoproteins. From the immunoisolated apoA-I-containing lipoproteins, we have isolated a subpopulation that has pre-beta mobility in contrast to the alpha mobility of most HDL. These pre-beta-migrating lipoproteins contain approximately 90% protein. The predominant apolipoprotein is apoA-I; neither apoB nor apoA-I1 were detected.