In vertebrates, the production of agmatine may be accomplished by ornithine decarboxylase (EC 4.1.1.17).
Mammalian paralogs of ornithine decarboxylase (fold-type III) were at one time attributed an arginine decarboxylase function, but subsequent studies proved that these proteins are not enzymes, but ornithine decarboxylase antizyme inhibitors (see ODCp).

In archaea such as M. jannaschii, arginine decarboxylase is pyruvoyl-dependent.