GPI-specific phospholipase D as an apolipoprotein

ABSTRACT

Glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) has recently been shown to be associated with high-density lipoproteins (HDL) in bovine serum. To determine the distribution of GPI-PLD among lipoproteins and characterize the GPI-PLD-containing lipoproteins in human plasma, we used dextram sulfate and immunoaffinity chromatography to isolate apolipoprotein-specific lipoproteins. This procedure allowed fractionation of lipoprotein particles into those containing apolipoprotein B (Lp B), apolipoproteins AI and AII (Lp AI/AII), or apolipoprotein AI only (Lp AI). In five plasma samples with HDL cholesterol ranging from 40 to 129 mg/dl, 75 ñ 12 percent (mean ñ SD) of the GPI-PLD activity was associated with LpAI, 11 ñ 13 percent with Lp AI/AII, while only 13 ñ 9 percent was present in plasma devoid of these lipoproteins, suggesting that most of the GPI-PLD in human plasma is associated with apolipoprotein AI. No GPI-PLD activity was detected in Lp B. Further characterization of the GPI-PLD-containing lipoproteins by gel filtration chromatography, nondenaturing poly-acrylamide and agarose gel electrophoresis revealed that GPI-PLD was restricted to an apolipoprotein AI-containing particle or complex that was small (apparent mean Mw of 140 KDa) and distinct from the bulk of HDL. Thus, the majority of plasma GPI-PLD appears to be specifically associated with a small, minor fraction of apoloprotein AI