A Combination of Unnatural Phosphatidyl Acceptor and Tandem Electrospray Ionization Mass Spectrometry for Tracing Phospholipase D Activity

Phospholipase D (PLD) is a biocatalyst in the synthesis of bioactive compounds and a key enzyme in a variety of biological signal transductions. A combination of unnatural phosphatidyl acceptor, N,N,N-triethyl-N-2-hydroxyethylammonium bromide 6, as a substrate for PLD, and tandem electrospray ionization mass spectrometry (ESI MS) was found to provide information as to whether a given phospholipid serves as a substrate for the PLD-catalyzed reaction. Thus 2-(13'-hydroperoxy-octadecadienoyl)-1-palmitoylglycerophosphocholine 1, and its degradation products 2-(13'-oxo-octadecadienoyl)-1-palmitoylglycerophosphocholine 9 and 2-(13'-hydroxy-octadecadienoyl)-1-palmitoylglycerophosphocholine 11, in a mixture were found to be a substrate of the PLD-catalyzed transphosphatidylation. The sensitivity of this method was exemplified by the observation that PLD activity in cabbage leaves was detected using a small amount of crude crushed leaves with little pretreatment. This simple method can be used in screening for PLD activity and searching for inhibitors of the enzyme from various natural sources.