ABSTRACTPolyphenol oxidase (EC 1.14.18.1) has been purified from Jerusalem artichoke tubers by immobilized copper affinity chromatography. The enzyme is primarily an o‐dihydroxyphenol oxidase with apparent Kmvalues of 1.9, 3.5 and 3.9 mM for chlorogenic acid, 4‐methylcatechol, and catechol, respectively. Several compounds exhibited inhibitory action for the enzyme in the order of: sodium metabisulfite>sodium diethyldithiocarbamate>2,3‐naphthalenediol>thioglycollate. Multiple forms were identified by gel filtration and SDS‐gradient polyacrylamide gel electrophoresis: two aggregates with apparent MW of 120 and 86 K and two monomeric subnits of 40–42 and 32–34 K, respectively. Concentration dependent association‐dissociation phenomena most likely determine the multimeric state of this enzyme. While the aggregated forms exhibited specificity towards mono‐, di‐ and polyhydroxyphenols, the low MW subunits were found active only with o‐dihydroxyphenols. The isoelectric points of the various enzyme species were within the range of 4.0 to 10.0. The enzyme was found to contain appreciable amounts of associated ca