title: Cholesterol relieves the inhibitory effect of sphingomyelin on type II secretory phospholipase A2.
abstract: Secretory type II phospholipase A2 (sPLA2) is inhibited by sphingomyelin (SPH); cholesterol either mixed with the model glycerophospholipid substrate or added to the assay medium as separated liposomes counteracts this inhibition efficiently. The inhibition of fatty acid release assayed by quantitative gas chromatography-MS is observed when SPH is added to erythrocyte membranes as the substrate instead of a readily hydrolysable phosphatidylethanolamine/phosphatidylserine model mixture. Hydrolysis of SPH by Staphylococcus aureus sphingomyelinase suppresses its inhibitory potency. The addition of cholesterol to SPH liposomes with a 1:1 stoichiometry relieves completely the inhibition of sPLA2 exerted by SPH. The mechanism of inhibition suggested by the binding assay is that sPLA2 binds with affinity to the SPH interface, after either phase segregation at the assay temperature or on the pure SPH liposomes added to the incubation medium. Cholesterol is shown to suppress the binding affinity of the enzyme for the SPH interface. A model for inhibition is suggested in which binding of the sphingosine moiety is competitive for sPLA2 (inhibition) or for cholesterol (release of the enzyme).
authors.affiliation: Laboratoire de Biochimie, URA CNRS 1283, Faculté de Médecine Saint Antoine, Université Pierre et Marie Curie, 27 rue Chaligny, 75571 Paris Cedex 12, France.
authors.forename: K S
authors.initials: KS
authors.lastname: Koumanov
authors.forename: P J
authors.initials: PJ
authors.lastname: Quinn
authors.forename: G
authors.initials: G
authors.lastname: Béréziat
authors.forename: C
authors.initials: C
authors.lastname: Wolf
mesh_terms: D000818:Animals; D002784:Cholesterol / Q000494:pharmacology*; D004347:Drug Interactions; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000201:enzymology; D005347:Fibroblasts / Q000187:drug effects / Q000201:enzymology; D054501:Group II Phospholipases A2; D006868:Hydrolysis; D008081:Liposomes; D051379:Mice; D010741:Phospholipases A / Q000037:antagonists & inhibitors*; D054467:Phospholipases A2; D013109:Sphingomyelins / Q000494:pharmacology*; D013211:Staphylococcus aureus; D014162:Transfection
chemical_list: D008081:Liposomes; D013109:Sphingomyelins; D002784:Cholesterol; D010741:Phospholipases A; D054501:Group II Phospholipases A2; D054467:Phospholipases A2