Identification and analyses of individual molecular species present in purified bovine heart ethanolamine glycerophospholipida.

aBovine heart lipids were extracted by a modified Bligh and Dyer procedure [21] and the ethanolamine phospholipid (PtdEtn) fraction was separated by using HPLC as previously described [23]. Analyses of PtdEtn molecular species were performed in the negative-ion mode by using an LTQ-Orbitrap mass spectrometer with an electrospray ion source. The determined monoisotopic masses (column 1) of PtdEtn molecular species were externally calibrated relative to the base peak. The molecular formulas listed in column 2 were derived from accurate mass analyses of monoisotopic mass and were grouped into each isobaric mass. The prefix “a”, “d”, and “p” stand for alkyl-acyl PtdEtn, diacyl PtdEtn, and plasmalogen PtdEtn, respectively. The relative abundance listed in column 3 was normalized to the isobaric base peak of the ion at m/z 766.5 after 13C de-isotoping and represents X±SD of at least four different analyses. The notation m∶n represents the fatty acyl (or ether aliphatic) chain containing m carbons and n double bonds. The numbers in the parentheses represent the relative composition of each individual molecular species of an isobaric ion. The symbols of “” indicate that the data represent the best estimation from the analyses.bIdentification of individual pPtdEtn molecular species was performed based on both accurate mass analyses and acidic vapor treatment. Identification of individual aPtdEtn molecular species was performed based on the accurate mass analyses, the paired rule, and the information of the identified pPtdEtn counterparts as discussed in the text. Identification of individual dPtdEtn molecular species was conducted solely based on accurate mass analyses. The abundance of each of the paired dPtdEtn molecular species cannot be accurately determined at the current stage of lipidomic technology.