Neutral glycerophospholipids

The neutral glycerophospholipids, PC and phosphatidylethanolamine (PE), make up the bulk of the complex lipids derived from glycerophosphoric 

Kayganich-Harrison and Murphy (1994a) employed negative ion FAB/ MS/MS together with stable isotope labelling to assess directly events of biosynthesis and metabolism of arachidonic acid-containing PL molecular species by cells in culture. Mast cells, cultured with [ C] linoleic acid, converted it into arachidonic acid which was then incorporated into cellular PLs. Over a 24 h period, the extent of label enrichment in each arachidonate-containing PL molecular species was monitored. Specific incorporation of [ CnJ-labelled arachidonate was determined from the ratio of the carbox-ylate anions at m/z 320 and 303, which correspond to [ Cn] arachidonate and unlabelled arachidonate, respectively. The carboxylate anions were produced by CID of each specific molecular anion. 

Kim and Salem (1986) developed a technique for rapid and detailed molecular species analysis of PL with use of reversed-phase HPLC with on-line TS/MS. In conjunction with a hexane/methanol/0.2 m ammonium acetate mixture as mobile phase, the technique was generalized for natural mixtures of PC and PE. The positive ion spectra of PC gave fragments similar to those of ammonia Cl, but the TS produced much simpler spectra, with extremely low background. As an example, 16 0/18 1 GPC gave the DG ion at m/z 578, the result of a loss of the phosphocholine group. The ions derived from phosphocholine were detected at m/z 142 and 184, with the peak at m/z 142 usually more intense than that of m/z 184. The molecular ion was present as a protonated form at m/z 761. The m/z 142 ion was monitored for the detection of PC. Coupling of reversed-phase HPLC with MS detection allowed an extensive separation of the molecular species of egg yolk PC. The DG ion peaks, which are predominant in the TS spectra of PC, allowed an easy reconstruction of the 10 major molecular species of PC. 

Wang and Ma (1994) used 0.5% ammonium hydroxide in a water/ methanol/hexane mixture and a Cl8 column to resolve complex mixtures of molecular species of PLs, which were detected as protonated and sodiated molecular species. Samples were injected onto a C18 HPLC column (5 pm, 2.1 mm X 15 cm) and separated by means of the aforementioned mobile phase changing linearly from 12 88 0 to 0 88 12 in 17 min after holding at the initial composition for 3 min. The column flow rate was 0.5 ml min and the effluent was split 1 100. The capillary exit voltage was generally set at 200 V and raised up to 300 V for the detection of DG ions. 

Substantial amounts of 18 1 and 18 0-alkyl PAF and 16 0-acyl-PAF were also identified. 

---

Jungalwala, Evans and McCluer (1984) were the first to combine HPLC with on-line FAB/MS for the analysis of glycerophospholipids. Separation of PL was achieved on a Brownlee silica gel cartridge column with ammonia-containing solvent as described for neutral PLs (subsection on choline... 

NLS neutral loss scan or scanning NMR nuclear magnetic resonance OPDA oxo-phytodienoic acid PA phosphatidic acid PC choline glycerophospholipid(s)... 

Glycerophospholipids are important components of biological membranes and are thus widely spread in nature. Partially purified products are used for a variety of applications, with soya lecithin as a typical example. Enzymes can be used to modify glycerophospholipids in various ways and in the surfactant area removal of one of the fatty acids to make lysophospholipids is the most important example. Sometimes this reaction is carried out only to make it easier to remove the phospholipids fraction from the neutral fat, such as in the processing of vegetable oils. This enzymatic de-gumming is an important industrial process [20]. In other applications, lysophospholipids are produced in order to improve the emulsifying properties of the lipids. One such example is in the preparation of mayonnaise, with improved emulsion stability [21]. In this application, phospholipase A2 is used selectively to remove the fatty acid in the sn-2 position. 

---