Phosphatidylserine decarboxylases (PSDs; EC 4.1.1.65) catalyze the formation of phosphatidylethanolamine (PE) by decarboxylation of phosphatidylserine (PS). Type I PSDs, such as PISD, are targeted to the inner mitochondrial membrane by an N-terminal targeting sequence. PISD also contains a conserved LGST motif that functions as an autocatalytic cleavage site where the proenzyme is split into mature alpha and beta subunits (Schuiki and Daum, 2009 [PubMed 19165886]).[supplied by OMIM, Jul 2010]