These enzymes are collectively known as group IV decarboxylases [<cite idref="PUB00001452"/>].Pyridoxal-dependent decarboxylases acting on ornithine, lysine, arginine andrelated substrates can be classified into two different families on the basisof sequence similarities [<cite idref="PUB00003632"/>, <cite idref="PUB00001452"/>].Members of this family while most probably evolutionary related, do not shareextensive regions of sequence similarities. This site contains a conserved lysine residue which is known, in mouse ODC [<cite idref="PUB00002726"/>], to be the site of attachment of thepyridoxal-phosphate group.