Catalyzes the decarboxylation of L-tyrosine to produce tyramine (PubMed:31196984). Plays a role in acid resistance since tyramine production via tyrosine decarboxylation appears to provide a cytosolic pH maintenance mechanism that helps the bacterium cope with acid stress such as that encountered in gastrointestinal tract (GIT) environments. Therefore, may contribute to the colonization of the human GIT by E.faecalis (By similarity). Also involved in drug metabolism, being able to catalyze decarboxylation of levodopa (L-dopa) to dopamine. In gut microbiota this enzyme is in fact exclusively responsible for the decarboxylation of levodopa, and thus reduces in situ levels of levodopa in the treatment of Parkinson's disease. It was shown that abundance of bacterial tyrosine decarboxylase in the proximal small intestine - the primary site of levodopa absorption - contributes to interindividual variation in drug efficacy and can explain the requirement for an increased dosage regimen of levodopa treatment in Parkinson's disease patients. H(+) + L-tyrosine = CO2 + tyramine H(+) + L-dopa = CO2 + dopamine (S)-alpha-fluoromethyltyrosine (AFMT) specifically inhibits microbial L-dopa decarboxylase activity, including in Parkinson's disease patient microbiotas. AFMT shows potential to block degradation of L-dopa by E.faecalis in mice. Blocking bacterial L-dopa decarboxylase activity in patients with Parkinson's disease, with knowledge of the abundance of this enzyme in an individual, could personalize and potentially improve L-dopa therapies. In contrast, L-dopa decarboxylation by E.faecalis is not inhibited by carbidopa, a commonly used human L-dopa decarboxylase inhibitor. kcat is 63.6 sec(-1) for the decarboxylation of L-tyrosine. kcat is 55.5 sec(-1) for the decarboxylation of L-dopa (at pH 5.5). L-dopa decarboxylation occurs more rapidly at lower pH, suggesting that this metabolism is likely accelerated at the lower pH of the upper small intestine. Amino-acid metabolism. Homodimer. Cells lacking this gene lose the ability to decarboxylate L-dopa, and display no growth defects compared with wild type. Belongs to the group II decarboxylase family. Tyrosine decarboxylase subfamily.