Hydrolysis of phosphatidylethanolamine induced by nominally synthetic lysophosphoglycerides: methodological implications.

Synthetic lysophosphatidylethanolamine (LPE) obtained from commercial sources augmented the apparent activity of phospholipase A2 (PLA2) in cardiac mitochondrial and microsomal fractions. For elucidation of this phenomenon, 2-[1-14C]linoleylphosphatidylethanolamine was incubated in the absence of cell protein with selected concentrations of LPE, lysophosphatidylcholine (LPC), Ca2+, ionic and nonionic detergents, and phospholipids with functional groups similar to those of LPE. Hydrolysis of phosphatidylethanolamine (PE) was evaluated by measurement of 14C-labeled free fatty acid release and confirmed by quantification of [14C]ethanolamine-labeled LPE formed. The reaction was dependent on the concentrations of Ca2+, PE, and LPE, exceeding 1.5 nmol/h with 20 micro M LPE and 30 micro M PE. Hydrolysis occurred in the presence of as little as 1 micro M LPE. PE was not hydrolyzed by comparable concentrations of ionic or nonionic detergents or by several closely related phosphatides, including LPC. Purification of synthetic LPE by high-performance LC to remove contaminating PLA2 eliminated the effect. LPE-induced hydrolysis of PE was found to depend on contamination of the LPE by PLA2 from Crotalus atrox, employed in the commercial synthesis of the lysophosphatide from the precursor used, phosphatidylethanolamine. Contamination of commercially obtained lysophosphoglycerides by PLA2 constitutes a technical pitfall which may cloud interpretation of experiments performed with inadequately purified material.