title: A turbidometric assay for phospholipase C and sphingomyelinase.
abstract: We describe a simple turbidometric assay for phosphatidylcholine-specific phospholipase C (PC-PLC) (EC 3.1.4.3), phosphatidylinositol-specific phospholipase C (PI-PLC) (EC 3.1.4.10), and sphingomyelinase (SMase) (EC 3.1.4.12), suitable for high-volume screening using unmodified substrates. Under the conditions described, 1 to 10 U/ml of PC-PLC (Bacillus cereus) induces a rapid and continuous increase in turbidity (0.4 to 0.6 AU at 410 nm) of phosphatidylcholine vesicles (1-10 mM) that highly correlates with hydrolysis. Turbidity increases with the formation of small homogenous particles, which is enzyme and substrate dependent. Analogously, PI-PLC (1-10 U/ml) causes a continuous increase in the turbidity of PI vesicles. SMase also causes a continuous increase in PC vesicle turbidity, but unlike like the glycerol phospholipases, SMase causes a discontinuous increase in vesicles of its proper substrate sphingomyelin (SM). After 8-15% hydrolysis, SM vesicles are converted to large heterogeneous particles permitting detection of SMase activity by visual inspection. Thus, turbidity is a useful property to monitor SMases and C-type phospholipases that cleave vesicle-forming phospholipids. Furthermore, the assay is designed for the microtiter plate format, enabling the continuous and simultaneous monitoring of up to 96 wells.
authors.affiliation: Oncology Section, Lederle Laboratories Division of American Cyanamid, Pearl River, New York 10965.
authors.forename: L
authors.initials: L
authors.lastname: Torley
authors.forename: C
authors.initials: C
authors.lastname: Silverstrim
authors.forename: W
authors.initials: W
authors.lastname: Pickett
mesh_terms: D006868:Hydrolysis; D008081:Liposomes; D009391:Nephelometry and Turbidimetry / Q000379:methods*; D010713:Phosphatidylcholines / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013108:Sphingomyelin Phosphodiesterase / Q000032:analysis*; D013997:Time Factors; D017186:Titrimetry; D010738:Type C Phospholipases / Q000032:analysis*
chemical_list: D008081:Liposomes; D010713:Phosphatidylcholines; D010738:Type C Phospholipases; D013108:Sphingomyelin Phosphodiesterase