The purification and properties of pig-liver catechol-O-methyl transferase

A procedure utilising affinity chromatography is described for the large-scale purification of pig-liver catechol-O-methyl transferase. The enzyme prepared by this method appears to be homogeneous by polyacrylamide gel electrophoretic criteria and gel chromatography. It is stable for prolonged periods when stored at -5 degrees C in 20% (v/v) glycerol. The enzyme has a molecular weight of about 23000 and does not appear to be a compound of subunits, or to associate to any appreciable degree. The pH optimum of the enzyme's activity is approximately pH 7.1--7.4, it does not catalyse the methylation of benzimidazole and has a Km of 0.64 mM and 0.056 mM towards 3,4-dihydroxyphenylacetic acid and S-adenosyl-L-methionine, respectively. Amino acid analysis showed the presence of five cysteine residues.