Phospholipase D (PLD)

Phospholipase D is an enzyme which is located in the plasma membrane and catalyzes the hydrolysis of phosphatidylcholine to form phosphatidic acid (PA), releasing the soluble choline headgroup into the cytosol. There are two mammalian isoforms of phospholipase D: PLD1 and PLD2. PLD directly interacts with kinases like PKC, ERK, TYK and controls the signalling indicating that PLD is activated by these kinases.

As choline is very abundant in the cell, PLD activity does not significantly affect choline levels, and choline is unlikely to play any role in signalling.  Phosphatidic acid is a signal molecule and acts to recruit SK1 to membranes. PA is extremely short lived and is rapidly hydrolysed by the enzyme PA phosphohydrolase to form diacylglycerol (DAG).