Activity of phosphatidylinositol-specific phospholipase C from Bacillus cereus with thiophosphate analogs of dimyristoylphosphatidylinositol.
Phosphatidylinositol-specific phospholipase C (PI-PLC) was studied with sonicated dispersions of a thiophosphate analog of phosphatidylinositol, 1, 2-dimyristoyloxypropane-3-thiophospho(1D-1-myo-inositol) (D-thio-DMPI). Kinetic parameters were derived from the rate as a function of bulk lipid concentration at constant saturating surface concentration of substrate (case I), and as a function of surface concentration of substrate at a constant saturating bulk concentration of lipid (case II). The substrate, D-thio-DMPI, was diluted with L-thio-DMPI or dimyristoyl phosphatidylmethanol (DMPM). In the presence of L-thio-DMPI, values for Vmax = 133 mumol min-1 mg-1, Ks' (the apparent dissociation constant for the enzyme-interface complex) = 0.097 mM, and Km* (the apparent interfacial Michaelis constant) = 0.22 mol fraction were obtained. DMPM caused enzyme inhibition in case I but no inhibition in case II. L-Thio-DMPI is an ideal neutral diluent with which to study the kinetics of PI-PLC.
Hendrickson
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Department of Chemistry, University of Washington, Seattle 98195, USA. hend@u.washington.edu
Giles
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D001409:Bacillus cereus / Q000201:enzymology*; D001426:Bacterial Proteins / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D008055:Lipids / Q000737:chemistry; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D010716:Phosphatidylinositols / Q000737:chemistry / Q000378:metabolism*; D054801:Phosphoinositide Phospholipase C; D010743:Phospholipids / Q000737:chemistry; D013010:Sonication; D013438:Sulfhydryl Compounds / Q000737:chemistry / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism*
D001426:Bacterial Proteins; D008055:Lipids; D010716:Phosphatidylinositols; D010743:Phospholipids; D013438:Sulfhydryl Compounds; C109946:dimyristoyloxypropanethiophosphoinositol; D010738:Type C Phospholipases; D054801:Phosphoinositide Phospholipase C; D043265:Phosphatidylinositol Diacylglycerol-Lyase