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 °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.