Which of the following phospholipids is least abundant in biological membranes?
Bulk membrane construction requires millimolar quantities of phosphatidylcholine and phosphatidylethanolamine structural lipids while phosphatidic acid remains trace because it functions primarily as biosynthetic intermediate and transient second messenger rather than barrier component. Phosphatidic acid generated de novo via glycerol three phosphate acyltransferase GPAT and one acylglycerol three phosphate acyltransferase AGPAT and by phosphorylation diacylglycerol via diacylglycerol kinases DGK alpha phosphorylating DAG kinases. Immediate conversion proceeds via CDP DAG synthases CDS1 CDS2 to CDP DAG fueling PI PG and cardiolipin synthesis and via lipin phosphatidate phosphatases LPIN1 to DAG for PC PE TAG synthesis. Signaling PA produced by phospholipase D PLD1 PLD2 hydrolyzing PC rapidly degraded within minutes by lipid phosphate phosphatases LPP. Consequently steady state mole fraction below one percent contrasts PC forty percent. Low abundance grants high signaling fidelity for recruitment of mTOR FRB Sos PH NADPH oxidase via specific PA binding domains. This explains why PA quantification requires sensitive mass spectrometry versus abundant choline lipids easily detected in lipidomics workflows.
Ref: Tanguy et al., Cellular Signalling, Phosphatidic acid metabolism low abundance and signaling.