Enhanced association of platelet-activating factor acetylhydrolase with lipoprotein (a) in comparison with low density lipoprotein.
Paired samples of human Lipoprotein (a) (Lp(a)) and low density lipoprotein (LDL) were assayed for their platelet-activating factor (PAF) acetylhydrolase activity. Lp(a) displayed markedly enhanced PAF acetylhydrolase activity (approximately 7-fold based on equal particle concentrations) in comparison to LDL isolated from the same individual. Lp(a)-associated acetylhydrolase exhibited properties observed for LDL-associated acetylhydrolase as well as for the purified enzyme; significant inhibition was obtained by treatment with diisopropylfluorophosphate (1 mM, 90%) and phenylmethanesulfonyl fluoride (5 mM, 50%). Furthermore, the hydrolytic activity of both lipoproteins was abolished with paraoxon (6 mM, IC50 0.9 mM) and with the fluorescent and active site-directed probe 4-hexyl-(6'-O-butyl-(4'-pyrenyl))-benzoic estersulfonyl fluoride (2) (KI(inact) = 525 microM), a novel irreversible inhibitor of PAF acetylhydrolase. Treatment with 2 and subsequent quantitation of protein-bound fluorescence suggests an increased concentration of enzyme associated to Lp(a) rather than alterations of kinetic constants due to the additional apolipoprotein apolipoprotein (a). Exposure of Lp(a) to Cu2+ (20 microM, 37 degrees C) was followed by a concomitant decrease of hydrolytic activity. A reduction of the basal activity by 91% was found after 15 h. Whereas immunoprecipitation with anti-apoB antiserum could remove enzymatic activity of Lp(a) regardless of a reductive treatment with dithiothreitol, precipitation with anti-apolipoprotein (a)-antibodies was accompanied by a minor reduction (approximately 30%) of the PAF-hydrolyzing ability. These results suggest that PAF acetylhydrolase exhibits an enhanced association with Lp(a) due to an increased affinity to Lp(a) apolipoprotein B.
Blencowe
C
C
Pharmazeutisch-Chemisches Institut, Universität Heidelberg, Germany.
Hermetter
A
A
Kostner
G M
GM
Deigner
H P
HP
D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; D000595:Amino Acid Sequence; D005456:Fluorescent Dyes; D006019:Glycolysis; D006801:Humans; D017270:Lipoprotein(a) / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011721:Pyrenes; D013050:Spectrometry, Fluorescence
C097502:6-((4-(pyrenyl)butyl)oxy)hexyl 4-fluorosulfonylbenzoate; D005456:Fluorescent Dyes; D017270:Lipoprotein(a); D008077:Lipoproteins, LDL; D011721:Pyrenes; D010741:Phospholipases A; D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase