Catalyzes the decarboxylation of L-tyrosine to produce tyramine (PubMed:24211777, PubMed:27292129). Cannot use other aromatic L-amino acids as substrates like L-phenylalanine, L-tryptophan and L-glutamate (PubMed:24211777). Is also able to decarboxylate the Parkinson's disease medication levodopa (L-dopa) to dopamine in vitro. H(+) + L-tyrosine = CO2 + tyramine H(+) + L-dopa = CO2 + dopamine kcat is 343.1 sec(-1) for the decarboxylation of L-tyrosine (PubMed:24211777). kcat is 124.8 sec(-1) for the decarboxylation of L-tyrosine. kcat is 76.5 sec(-1) for the decarboxylation of L-dopa (PubMed:27292129). Optimum pH is 5.0 for the decarboxylation of L-tyrosine. Is not active at pH below 3.5 or above 9.0. More than 90% of activity remains over pH range from 5.0 to 6.0, and activity decreases rapidly at pH below 5.0 or higher than 6.0. Optimum temperature is 50 degrees Celsius. Only 8.5% of activity remains at 70 degrees Celsius. However, the enzyme shows poor stability at 50 degrees Celsius, the relative activity dropped to 14% after 1 h of incubation. Amino-acid metabolism. Homodimer. 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. Belongs to the group II decarboxylase family. Tyrosine decarboxylase subfamily.