Differentiation of 1-O-alk-1′-enyl-2-acyl and 1-O-alkyl-2-acyl Glycerophospholipids by Multiple-Stage Linear Ion-Trap Mass Spectrometry with Electrospray Ionization

Abstract

We described linear ion-trap mass spectrometric approaches applying MS(3) and MS(4) toward to the structural characterization of 1-O-alk-1'-enyl-2-acyl-, 1-O-alkyl-2-acyl-, and diacyl-glycerophospholipids (GPL) as the [M - H](-) ions desorbed by ESI in negative-ion mode. Further dissociation of the [lM - H - R(2)CO(2)H - polar head group](-) ions from the [M - H](-) ions of GPL that have undergone the consecutive losses of the fatty acid substituent at sn-2 and the polar head group readily gives the structural information of the radyl group at sn-1, resulting in structural differentiation among the 1-O-alk-1'-enyl-2-acyl-, 1-O-alkyl-2-acyl, and diacyl-glycerolphospholipid molecules. The distinction between a 1-O-alk-1'-enyl-2-acyl- and a 1-O-alkyl-2-acyl-GPL is based on the findings that the MS(3) (or MS(4)) spectrum of the [M - H - R(2)CO(2)H - polar head group](-) ion from the former compound is dominated by the alkenoxide anion that represents the radyl moiety at sn-1, while the spectrum from the latter compound is dominated by the ion at m/z 135 arising from further loss of the 1-O-alkyl group as an alcohol. Another important notion is that the optimal collision energy required for acquiring the former spectrum is significantly lower than that required for obtaining the latter spectrum. Using the approaches, we are able to reveal the structures of several isobaric isomers in GPL mixtures of biological origin. Because the [M - H](-) ions are readily formed by various GPL classes (except glycerophosphocholine) in the negative-ion mode, these mass spectrometric approaches should have broad application in the structural identification of GPLs.

Instability of the cellular lipidome with age

“…The major contributors to total LPE concentration were 1-O-alkyl ethers, the most (Fig. S1) as previously described (Hsu and Turk 2007). Total LPEs decreased with age but did so in a much more gradual manner than the other GPs and also did not plateau.…”

Identification of atypical ether-linked glycerophospholipid species in macrophages by mass spectrometry

“…All of the above peak assignments are in good correlation with previously reported data for PS and PT mass spectral analyses (27)(28)(29). Over 30 PT species were identifi ed in different mac- were observed all in agreement with previously published data ( 21,31,32 ). As with all plasmanyl PE and PC, there were no fragments corresponding to the alkyl moiety, but just fragments arising from the loss of the acyl moiety, thus creating ether-containing lyso lipid fragments and their dehydrated forms.…”

“…The representative MS/MS spectrum on 331.1 is also present. Here again, the ions corresponding to the radyl substituents at sn-1 are not detected in agreement with previously shown fragmentation of plasmanyl phospholipids ( 21 ). We hypothesize that the ether and vinyl ether PA, PI, and PS glycerophospholipids reported above are direct or indirect products from the biosynthesis of plasmanyl and rophages (proposed phospholipid species presented in Table 2 ).…”

Profiling changes triggered during maturation of dendritic cells: a lipidomic approach

“…ESI-MS analysis of the PE spot was performed in negative mode and revealed that major diacyl-PE species correspond to [M − H] − with m/z Table 2 [34,35,37,38]. All these components were confirmed by study of the fragmentation pathways observed in the MS-MS spectra, which enabled identification of the composition of fatty acyl residues of both diacyl-PE and alkenyl-PE and the most probable location along the glycerol backbone [34]. Diacyl-PE species with [M − H] − m/z 742.5, the most prevalent PE, was taken as an example, thus, their study by MS-MS revealed two abundant RCOO − ions at m/z 281 and m/z 279, that correspond to oleic (C18:1) and linoleic (C18:2) fatty acids, respectively.…”