A rapid phospholipase D assay using zirconium precipitation of anionic substrate phospholipids: application to N-acylethanolamine formation in vitro

Gitte Petersen,Kent D Chapman,Harald S Hansen

doi:10.1016/s0022-2275(20)33466-0

Abstract

Activation of phospholipase D (PLD) is involved in a number of signal transduction pathways in eukaryotic cells. The most common method for determination of PLD activity in vitro involves incubation with a radiolabeled substrate and lipid extraction followed by thin-layer chromatography in order to separate and quantify substrate and product(s). A more rapid assay can be used when utilizing phosphatidylcholine as a substrate because one of the products, choline, is water soluble and therefore easily separated from the substrate. However, this separation principle is not applicable in evaluating N-acylphosphatidylethanolamine (NAPE)-hydrolyzing PLD activity, which produces two lipophilic products, N-acylethanolamine (NAE) and phosphatidic acid. Therefore, we developed a rapid assay for the routine detection of NAPE-hydrolyzing PLD activity. This assay is based on precipitation of radiolabeled substrate (NAPE) in the presence of ZrOCl(2), followed by quantification of radiolabeled NAE released into a methanolic supernatant. The precipitation involves a chemical reaction of the zirconyl cation with the phosphate anion. Conditions were optimized for the complete precipitation of NAPE, whereas N-acyllysophosphatidylethanolamine and glycerophospho(N-acyl)ethanolamine were precipitated at least 95%. Furthermore, this precipitation method can be extended to assays of other anionic phospholipid-hydrolyzing PLD activities by selecting an optimal pH of the precipitation solution. For example, 98;-99% precipitation of phosphatidylethanolamine, phosphatidylglycerol, and phosphatidylserine was achieved.Consequently, this new assay allows for a convenient examination of PLD activities toward a variety of phospholipid substrates, and in particular allows for the analysis of NAE formation from NAPE in vitro, a feature that will facilitate a more complete biochemical characterization of this anandamide-generating enzyme.

Highlights

Activation of phospholipase D (PLD) is involved in a number of signal transduction pathways in eukaryotic cells
200 micrograms of microsomal fraction from various cow tissues was incubated in duplicate (TLC samples) or triplicate (LSC samples) for 0, 15, 30, 60, and 120 min at 37ЊC with 2 nmol of 1,2-dilauroyl-snglycero-3-phospho(N-[1Ј-14C]palmitoyl)ethanolamine (NAPE; 5,000 dpm/nmol) in a total volume of 200 ␮l of 60 mm bis-Tris propane (BTP), 2 mm DTT, Triton X-100 (0.4 mg/ml), pH 8.0, 10 mm PMSF, and 5 ␮l of DMSO
This will not influence the detection of NAPE-PLD activity in the zirconium assay because free fatty acids will not be precipitated by zirconium

Summary

Introduction

Activation of phospholipase D (PLD) is involved in a number of signal transduction pathways in eukaryotic cells. A more rapid assay can be used when utilizing phosphatidylcholine as a substrate because one of the products, choline, is water soluble and separated from the substrate This separation principle is not applicable in evaluating N-acylphosphatidylethanolamine (NAPE)-hydrolyzing PLD activity, which produces two lipophilic products, N-acylethanolamine (NAE) and phosphatidic acid. Conditions were optimized for the complete precipitation of NAPE, whereas N-acyllysophosphatidylethanolamine and glycerophospho(Nacyl)ethanolamine were precipitated at least 95% This precipitation method can be extended to assays of other anionic phospholipid-hydrolyzing PLD activities by selecting an optimal pH of the precipitation solution. 98–99% precipitation of phosphatidylethanolamine, phosphatidylglycerol, and phosphatidylserine was achieved This new assay allows for a convenient examination of PLD activities toward a variety of phospholipid substrates, and in particular allows for the analysis of NAE formation from NAPE in vitro, a feature that will facilitate a more complete biochemical characterization of this anandamide-generating enzyme.—Petersen, G., K.

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