Structural Analysis of Phosphatidylinositol from Carrot Cell Membranes by Fast Atom Bombardment and Tandem Mass Spectrometry

Abstract

Inositol phospholipids from carrot cell membranes grown in suspension culture were partially purified by silicic acid column chromatography and then determined by negative ion fast atom bombardment mass spectrometry (FAB). Deprotonated molecules, [M - H]−, were detected of the phosphatidylinositol (PI) and other phospholipids in the column effluent. Following FAB desorption, the structure of carrot PI was determined by using tandem mass spectrometry (MS/MS) with collisional activation. First, inositol phospholipids were differentiated from other phospholipids in the column effluent by using constant neutral loss MS/MS to identify which [M - H]− ions fragmented to eliminate neutral inositol (i.e., [M - H - 162]− ions). Next, collisional activation of the [M - H]− ion of PI at m/z 833 was combined with B/E linked scanning to obtain additional structural information such as the presence of the glycerol and fatty acid moieties, and additional confirmation of the inositol phosphate. Charge-remote fragmetation was used to determine the structure of each fatty acid group bound to PI. Finally, B/E linked scanning of [M - H - inositol]− ion at m/z 671 was used to determine the location of each fatty acid group on the glycerol chain of PI.