The enzyme phosphatidylserine decarboxylase (EC 4.1.1.65) catalyzes the chemical reaction

phosphatidyl-L-serine ${\displaystyle \rightleftharpoons }$ phosphatidylethanolamine + CO₂

This enzyme belongs to the family of lyases, specifically the carboxy-lyases, which cleave carbon-carbon bonds. The systematic name of this enzyme class is phosphatidyl-L-serine carboxy-lyase (phosphatidylethanolamine-forming). Other names in common use include PS decarboxylase, and phosphatidyl-L-serine carboxy-lyase. This enzyme participates in glycine, serine and threonine metabolism, and glycerophospholipid metabolism. It has two cofactors: pyridoxal phosphate, and Pyruvate.