Three classes of arginine decarboxylase exist, of which two use the cofactor pyridoxal 5'-phosphate and a third uses a pyruvoyl group. Methanococcus jannaschii uses pyruvoyl-dependent arginine decarboxylase (PvlArgDC) to convert L-arginine into agmatine, which can be converted to putrescine by agmatine ureohydrolase. Putrescine can be used to biosynthesize polyamines. These are essential for cell growth and proliferation and are found in all organisms. Some pathogenic microorganisms, such as Chlamydia sp., are thought to import L-Arg from the host, decarboxylate it, and export the agmatine product, depleting the host's L-Arg supply and increasing the extracellular pH. Agmatine is also an inhibitor of nitric-oxide synthase and a suppressor of apoptosis. PvlArgDC is translated as a proenzyme (pi-chain), which cleaves itself between Ser52 and Ser53 by autocatalytic serinolysis to form two polypeptide (alpha and beta) chains. The alpha chain begins with the newly created pyruvoyl group, which is the cofactor in the decarboxylation reaction, and the smaller beta fragment terminates with a new carboxyl group at Ser52.