Mammalian L-amino acid decarboxylases producing 1,4-diamines: histidine decarboxylase (HDC), aromatic L-amino acid decarboxylase (DDC) and ornithine decarboxylase (ODC); and their products: histamine, serotonin, tryptamine and putrescine, exhibit functional, metabolic and enzymic properties in common. HDC has been related to very different topics: alergy, neurochemistry and cell proliferation, as also described for DD and ODC. The Host Group have detected some analogies among the deduced primary sequences of these proteins. The common protein motifs observed every mammalian L-amino acid decarboxylase could be involved in the rapid turnover of these enzymes and/or in the decarboxylation mechanisms. In order to check this hypothesis, we will study the post-translational modifications and activities of expressed recombinant cDNAs encoding the rat mature HDC subunit and directed mutant DNA sequences. The characterization of the molecular underlying mechanisms of L-amino acid decarboxylase turnover and catalysis mechanisms will provide important basis for therapeutic strategies in alergy, neurochemistry and cell proliferation fields.