Purification and properties of polyphenol oxidase from mango peel (Mangifera indica. Var. Raspuri)

Polyphenol oxidase from the peel of ripe mango fruit (Mangifera indica. Var. Raspuri) was purifed 126-fold to homogeneity by ammoniun sulphate fractionation, column chromatography on Blue Sepharose CL-6B and gel chromatography on Sephadex G-200. It had an iso-electric point (pI) of 4.1±0.2 and molecular weight of 137,000 daltons as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and gel filtration. It was more specific for catechol (than for other substatres tested) with a Km of 8.2 mM. 2-mercaptoethanol, L-cysteine, sodium diethyldithiocarbamate and thiourea were effective inhibitors of this enzyme. It had pH and temperature optima of 5.5 and 46°C, respectively. It lost 50% activity by exposure to 85°, 75° and 65°C for 3, 16 and 25.5 min, respectively. Copper content was one atom per mole of enzyme and copper was essential for its activity. Unlike most of the polyphenol oxidases, multiple forms were not detected in the crude extract