Composition of head groups
of a phospholipid bilayer of a cellular
membrane. Choline and ethanolamine are two main substrates for the
synthesis of phosphatidylcholine (PtC) and phosphatidylethanolamine
(PtE), respectively. PtC can be degraded via GPC to choline. Proteins
embedded in the cellular membrane are shown to be glycosylated. Abbreviations:
ADP, adenosine diphosphate; ATP, adenosine triphosphate; CDP, cytidine
diphosphate; CKI 1, choline kinase; CTP, cytidine triphosphate; ECT
phosphoethanolamine cytidylyltransferase; EK, ethanolamine kinase;
EPT, ethanolaminephosphotransferase; LPL, lysophospholipase; P-Eta,
phosphoethanolamine; P-choline, phosphocholine; PD, glycerophosphocholine
phosphodiesterase; PLA, phospholipase A2; and PPi, pyrophosphate.