GPI-specific phospholipase D associates with an apoA-I- and apoA-IV-containing complex

Glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) is abundant in serum and associates with high density lipoproteins (HDL), We have char acterized the distribution of GPI-PLD among lipoproteins in human plasma. A polipoprotein (apo)-specific lipoproteins containing apoB (Lp[B]), apoA-I a nd A-II (Lp[A-I, A-II]), or apoA-I only (Lp[A-I]) were isolated using dextr an sulfate and immunoaffinity chromatography, In six human plasma samples w ith HDL cholesterol ranging from 39 to 129 mg/dl, 79 +/- 14% (mean +/- SD) of the total plasma GPI-PLD activity was associated with Lp[A-I], 9 =/- 12% with Lp[A-I, A-II], and 1 +/- 1% with Lp[B]; and 11 +/- 10% was present in plasma devoid of these lipoproteins. Further characterization of the GPI-P LD-containing lipoproteins by gel-filtration chromatography and nondenaturi ng polyacrylamide and agarose gel electrophoresis revealed that these apoA- I-containing particles/complexes were small (8 nm) and migrated with pre-be ta particles on agarose electrophoresis. Immunoprecipitation of GPI-PLD wit h a monoclonal antibody to GPI-PLD co-precipitated apoA-I and apoA-IV but l ittle or no apoA-II, apoC-II, apoC-III, apoD, or apoE, In vitro, apoA-I but not apoA-IV or bovine serum albumin interacted directly with GPI-PLD, but did not stimulate GPI-PLD-mediated cleavage of a cell surface GPI-anchored protein, Thus, the majority of plasma GPI-PLD appears to be specifically as sociated with a small, discrete, and minor fraction of lipoproteins contain ing apoA-I and apoA-IV.