Catalyzes the decarboxylation of L-3,4-dihydroxyphenylalanine (DOPA) to dopamine, L-5-hydroxytryptophan to serotonin and L-tryptophan to tryptamine. H(+) + L-dopa = CO2 + dopamine 5-hydroxy-L-tryptophan + H(+) = CO2 + serotonin Homodimer. Belongs to the group II decarboxylase family.