Partial Purification and Characterization of Polyphenol Oxidase from Cocoyam,Xanthosoma sagittifolium

Polyphenol oxidase has been partially purified from Xanthosoma sagittifolium. The enzyme showed activity towards pyrogallol, DL-β-3,4-dihydroxyphenylalanine (DOPA) and catechol. Of these three, pyrogallol was the best substrate. The effects of various compounds as inhibitors of the reaction catalysed by the enzyme were tested. p-Nitrophenol competitively inhibited the binding of both catechol and pyrogallol to the enzyme. Inhibition by the substrate analogue, p-cresol was of the mixed type while thiourea and diethyldithiocarbamate inhibited the enzyme uncompetitively. The approximate molecular weight of the enzyme determined by gel filtration was 47 000.