Tyrosine decarboxylase (EC 4.1.1.25) (TDC) from the wine Lactobacillus brevis IOEB 9809 was purified by a rapid procedure involving anion exchange chromatography, ultrafiltration and hydrophobic interaction chromatography. The protein comprised two subunits of identical molecular mass (approximately 70000 Da). Enzyme activity was dependent on exogenously supplied pyridoxal 5'-phosphate and the enzyme was stable at 4 degrees C in the presence of the coenzyme. Optimum pH for the pure enzyme was 5.0. At this pH, TDC exhibited Michaelis-Menten kinetics (K(m) 0.63 mM, V(max) 998 units) and was highly substrate-specific for L-tyrosine. Other amino acids and L-DOPA are not converted by the protein. Tyramine acted as a mixed non-competitive inhibitor. Significant similarities in some biochemical properties were observed with the corresponding decarboxylase enzyme of Streptococcus faecalis, the sole bacterial TDC described to date.