Identification of carrot inositol phospholipids by fats atom bombardment mass spectrometry

Abstract

Inositol phospholipids from carrot cell membranes grown in suspension cultured were purified by thinlayer chromatography (TLC) or column chromatography and tentatively identified by co-migration on TLC with animal inositol phospholipid standards. For more rigorous chemical characterization, carrot inositol phospholipids were then analyzed by negative ion fast atom bombardment mass spectrometry (FABMS). One phosphatidylinositol (PI), two lysophosphatidylinositols (LPI), and one phosphatidylinositol monophosphate (PIP) were identified in the carrot samples by the observation of ions [M-H]⁻ and numerous fragment ions in the negative FAB mass spectra. MS/MS analysis were carried out to obtain further structural information of these phospholipids using a double-focusing mass spectrometer in which the magnetic sector (B) and the electrostatic analyzer (E) were scanned at a constant ratio (B/E). These B/E linked scans provided fragment ions of selected precursor ions while eliminating matrix and other contaminating ions. No molecular ions were detected for lysophosphatidylinositol monophosphate (LPIP) or phosphatidylinositol bisphosphate (PIP₂), but fragment ions corresponding to these structures were observed. The primary fatty acids present in the carrot inositol phospholipids were linoleic (18∶2) and palmitic (16∶0) acids, whereas animal lipids contained arachidonic (20∶4), stearic (18∶0), linoleic, and palmitic acids. The only phosphatidylinositol found in carrot cells was palmitoyl linoleoyl PI.