title: Isolation and characterization of phospholipase D from fababeans.
abstract: An enzyme activity in crude extract of fababeans hydrolyzed phosphatidylcholine-U-14C to produce choline and phosphatidic acid. This enzyme, phospholipase D, was stable at 50 C in the presence of 5 mM DTT but was inactivated at 55 C. The enzyme was precipitated with cold acetone, concentrated between 30% saturation to 40% saturation with ammonium sulphate, absorbed on calcium phosphate gel and eluted with 0.2 M phosphate buffer. This procedure resulted in a 20-fold increase in specific activity. The activity of fababean phospholipase D was much higher when assayed at 38 C than that at room temperature. There was an obligatory requirement for calcium, and for maximal activity 40 mM calcium was required. A narrow pH optimum of about pH 5.7 was observed. The enzyme activity was extremely dependent on substrate dispersion. When 5 mM phosphatidylcholine (PC) was sonicated with increasing levels of sodium dodecyl sulphate (1 mM to 4 mM), the enzyme activity kept increasing. By using equimolar concentrations of PC and sodium dodecyl sulphate (1 mM to 5 mM), the Michaelis constant (Km) was estimated to be 1.74 mM. Addition of choline and serine at 10 mM concentration reduced phospholipase D activity by 31% and 22%, respectively.
mesh_terms: D004355:Drug Stability; D007887:Fabaceae / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D010713:Phosphatidylcholines / Q000378:metabolism; D010739:Phospholipase D / Q000302:isolation & purification* / Q000378:metabolism; D010740:Phospholipases / Q000302:isolation & purification*; D010946:Plants, Medicinal; D013696:Temperature
chemical_list: D010713:Phosphatidylcholines; D010740:Phospholipases; D010739:Phospholipase D