Methanococcus jannaschii contains homologues of most genes required for spermidine polyamine biosynthesis. Yet genomes from neither this organism nor any other euryarchaeon have orthologues of the pyridoxal 5'-phosphate- dependent ornithine or arginine decarboxylase genes, required to produce putrescine. Instead,these organisms have a new class of arginine decarboxylase (PvlArgDC) formed by the self-cleavage of a proenzyme into a 5-kDa subunit and a 12-kDa subunit that contains a reactive pyruvoyl group. Although this extremely thermostable enzyme has no significant sequence similarity to previously characterised proteins, conserved active site residues are similar to those of the pyruvoyl-dependent histidine decarboxylase enzyme, and its subunits form a similar (alpha-beta)(3) complex. Homologues of PvlArgDC are found in several bacterial genomes, including those of Chlamydia spp., which have no agmatine ureohydrolase enzyme to convert agmatine (decarboxylated arginine) into putrescine. In these intracellular pathogens, PvlArgDC may function analogously to pyruvoyl-dependent histidine decarboxylase; the cells are proposed to import arginine and export agmatine, increasing the pH and affecting the host cell's metabolism. Phylogenetic analysis of Pvl- ArgDC proteins suggests that this gene has been recruited from the euryarchaeal polyamine biosynthetic pathway to function as a degradative enzyme in bacteria [1].

1: Pyruvoyl-dependent arginine decarboxylase from Methanococcus jannaschii: crystal structures of the self-cleaved and S53A proenzyme forms. Tolbert WD, Graham DE, White RH, Ealick SE; Structure. 2003;11:285-294. PMID:12623016