GPI-SPECIFIC PHOSPHOLIPASE-D AS AN APOLIPOPROTEIN

Glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) has re cently been shown to be associated with high-density lipoproteins (HDL ) in bovine serum. To determine the distribution of GPI-PLD among lipo proteins and characterize the GPI-PLD-containing lipoproteins in human plasma,we used dextran sulfate and immunoaffinity chromatography to i solate apolipoprotein-specific lipoproteins. This procedure allowed fr actionation of lipoprotein particles into those containing apolipoprot ein B (Lp B), apolipoproteins Al and AII (Lp AI/AII), or apolipoprotei n AI only (Lp AI). In five plasma samples with HDL cholesterol ranging from 40 to 129 mg/dl, 75 +/- 12% (mean +/- SD) of the GPI-PLD activit y was associated with Lp AI, 11 +/- 13% with Lp AI/AII, while only 13 +/- 9% was present in plasma devoid of these lipoproteins, suggesting that most of the GPI-PLD in human plasma is associated with apolipopro tein AI. No GPI-PLD activity was detected in Lp B. Further characteriz ation of the GPI-PLD-containing lipoproteins by gel filtration chromat ography, nondenaturing polyacrylamide and agarose gel electrophoresis revealed that GPI-PLD was restricted to an apolipoprotein AI-containin g 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 ap pears to be specifically associated with a small, minor fraction of ap olipoprotein AI.