title: Membrane lipid composition differentially modulates the function of human plasma platelet activating factor-acetylhydrolase.
abstract: Human plasma platelet activating factor-acetylhydrolase (HpPAF-AH) is a calcium-independent phospholipase that catalyzes the hydrolysis of ester bond at the sn-2 position of phospholipid substrates. The enzyme belongs to group VIIA of the phospholipase A₂ superfamily and is associated with the lipids. Circulating form of HpPAF-AH resides on the lipoprotein particles and acts on a wide variety of substrates, including oxidized phospholipids. In this study we have characterized the effect of lipid composition of the membrane vesicles on the function of purified HpPAF-AH. Lipid composition of the vesicles was varied by incorporating varying amounts of cholesterol in the matrix phospholipids, POPC and DPPC, and its effect on the membrane binding, membrane penetration and the activity of the enzyme was determined. Physicochemical properties of the phospholipid vesicles were characterized by using different fluorescent probes. For the first time our results show that (a) membrane binding of HpPAF-AH increases the activity of enzyme (interfacial activation) and (b) lipid composition of membrane vesicles, by changing the physicochemical properties, differentially modulates the binding, partial membrane penetration and the activity of the enzyme.
authors.affiliation: Department of Biotechnology, National Institute of Pharmaceutical Education and Research (NIPER), Sector 67, S.A.S. Nagar, Punjab 160062, India. apande@niper.ac.in
authors.forename: Abhay H
authors.initials: AH
authors.lastname: Pande
authors.forename: Vikas A
authors.initials: VA
authors.lastname: Tillu
mesh_terms: D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase / Q000737:chemistry / Q000378:metabolism*; D001792:Blood Platelets / Q000201:enzymology*; D002784:Cholesterol / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology; D006801:Humans; D008074:Lipoproteins / Q000737:chemistry / Q000378:metabolism; D010713:Phosphatidylcholines / Q000737:chemistry / Q000378:metabolism*; D054467:Phospholipases A2 / Q000737:chemistry / Q000378:metabolism
chemical_list: D008074:Lipoproteins; D010713:Phosphatidylcholines; D002784:Cholesterol; D054467:Phospholipases A2; D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; C526684:PLA2G7 protein, human; C028694:1-palmitoyl-2-oleoylphosphatidylcholine