title: Characterization of the yeast actin patch protein App1p phosphatidate phosphatase.
abstract: Yeast App1p is a phosphatidate phosphatase (PAP) that associates with endocytic proteins at cortical actin patches. App1p, which catalyzes the conversion of phosphatidate (PA) to diacylglycerol, is unique among Mg(2+)-dependent PAP enzymes in that its reaction is not involved with de novo lipid synthesis. Instead, App1p PAP is thought to play a role in endocytosis because its substrate and product facilitate membrane fission/fusion events and regulate enzymes that govern vesicular movement. App1p PAP was purified from yeast and characterized with respect to its enzymological, kinetic, and regulatory properties. Maximum PAP activity was dependent on Triton X-100 (20 mm), PA (2 mm), Mg(2+) (0.5 mm), and 2-mercaptoethanol (10 mm) at pH 7.5 and 30 °C. Analysis of surface dilution kinetics with Triton X-100/PA-mixed micelles yielded constants for surface binding (Ks(A) = 11 mm), interfacial PA binding (Km(B) = 4.2 mol %), and catalytic efficiency (Vmax = 557 μmol/min/mg). The activation energy, turnover number, and equilibrium constant were 16.5 kcal/mol, 406 s(-1), and 16.2, respectively. PAP activity was stimulated by anionic lipids (cardiolipin, phosphatidylglycerol, phosphatidylserine, and CDP-diacylglycerol) and inhibited by zwitterionic (phosphatidylcholine and phosphatidylethanolamine) and cationic (sphinganine) lipids, nucleotides (ATP and CTP), N-ethylmaleimide, propranolol, phenylglyoxal, and divalent cations (Ca(2+), Mn(2+), and Zn(2+)). App1p also utilized diacylglycerol pyrophosphate and lyso-PA as substrates with specificity constants 4- and 7-fold lower, respectively, when compared with PA.
authors: Department of Food Science, Rutgers Center for Lipid Research, and New Jersey Institute for Food, Nutrition, and Health, Rutgers University, New Brunswick, New Jersey 08901, USA.
authors: Minjung
authors: M
authors: Chae
authors: George M
authors: GM
authors: Carman
mesh_terms: D004075:Diglycerides / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008055:Lipids / Q000096:biosynthesis / Q000737:chemistry; D008823:Micelles; D008840:Microfilament Proteins / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism; D017830:Octoxynol / Q000737:chemistry; D010711:Phosphatidate Phosphatase / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism; D013379:Substrate Specificity / Q000502:physiology
chemical_list: D004075:Diglycerides; D008055:Lipids; D008823:Micelles; D008840:Microfilament Proteins; D029701:Saccharomyces cerevisiae Proteins; D017830:Octoxynol; C505432:APP1 protein, S cerevisiae; D010711:Phosphatidate Phosphatase