Abstract
Polyphenol 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 Km values 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 carbohydrate material.
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