Enables tyrosine decarboxylase activity. Involved in octopamine biosynthetic process. Located in axon and neuronal cell body. Expressed in hermaphrodite gonad and lateral ganglion. Human ortholog(s) of this gene implicated in several diseases, including aromatic L-amino acid decarboxylase deficiency; hyperinsulinism; and nicotine dependence. Is an ortholog of human DDC (dopa decarboxylase).