Figure 1 Glycerophospholipid classes and subclasses Figure 1 | Glycerophospholipid classes and subclasses. Different structures of the polar moiety (X), which are connected to the phosphate head group, define the individual glycerophospholipid (GPL) classes. The subclasses of phosphatidyl, plasmanyl and plasmenyl result from the different linkages (that is, ester, ether and vinyl ether) of a fatty acyl chain to the hydroxy group at the sn-1 position of glycerol. These subclasses are mainly present in choline and ethanolamine GPLs, although the presence of these subclasses in other GPL classes such as ether-containing serine GPL is reported154. The chains at R1, R'1 and R2 vary with different numbers of carbon atoms, numbers of double bonds and the location of the double bonds, to produce the individual molecular species of each lipid class. The cleavage sites of phospholipase A1 (PLA1), phospholipase A2 (PLA2), phospholipase C (PLC) and phospholipase D (PLD) are also indicated. Han, X. (2016) Lipidomics for studying metabolism Nat. Rev. Endocrinol. doi:10.1038/nrendo.2016.98