<p>Phosphatidylcholine-hydrolysing phospholipase D (PLD) isoforms are activated by ADP-ribosylation factors (ARFs). PLD produces phosphatidic acid from phosphatidylcholine, which may be essential for the formation of certain types of transport vesicles or may be constitutive vesicular transport to signal transduction pathways. PC-hydrolysing PLD is a homologue of cardiolipin synthase, phosphatidylserine synthase, bacterial PLDs, and viral proteins. Each of these appears to possess a domain duplication which is apparent by the presence of two motifs containing well-conserved histidine, lysine, and/or asparagine residues which may contribute to the active site aspartic acid. An <taxon tax_id="562">Escherichia coli</taxon> endonuclease (nuc) and similar proteins appear to be PLD homologues but possess only one of these motifs [<cite idref="PUB00005043"/>, <cite idref="PUB00005451"/>, <cite idref="PUB00002867"/>, <cite idref="PUB00000088"/>].</p> Phospholipase D/Transphosphatidylase