L-Methionine decarboxylase [EC 4.1.1.57] catalyzes the decarboxylation of L-methionine and is a pyridoxal 5'-phosohate(PLP)-dependent enzyme. L-Methionine decarboxylase has been purified 630-fold by DEAE-Toyopearl 650M, Phenyl-Toyopearl 650M and Sephacryl S-300 column chromatographies from Streptomyces sp.590. The enzyme has a dimeric structure with identical subunits of Mr 60,000. This enzyme shows optimum activity at pH7.0 and 45°C, and is stable between pH5.7 and pH9.0. L-Methionine decarboxylase has antitumor activity against RERF-LC-AI and HeLa cells. Ten N-terminal amino acid sequence of L-methionine decarboxylase was determined, and the sequence showed no homology with other reported proteins.