Catalyzes the decarboxylation of L-tyrosine to produce tyramine (PubMed:30659181). 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 (PubMed:25529314). 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 Levodopa decarboxylation is not inhibited by carbidopa, benserazide, and methyldopa, that are three human L-dopa decarboxylase inhibitors. kcat is 6963 min(-1) for the decarboxylation of L-tyrosine. kcat is 3531 min(-1) for the decarboxylation of L-dopa (at pH 5.0). Amino-acid metabolism. Homodimer. Up-regulated by tyrosine and acidic pH. Makes part of an operon together with tyrP and nhaC-2. Cells lacking the tdc cluster (tyrS, tdc/tdcA, tyrP and nhaC-2) lose the ability to produce tyramine, and show reduced viability under acidic pHs in the presence of tyrosine. Belongs to the group II decarboxylase family. Tyrosine decarboxylase subfamily. Truncated N-terminus.