Purification of the Glycosylated Polyphenol Oxidase from Potato Tuber

Glycosylated polyphenol oxidase was purified from potato tuber using ammonium sulfate fractionation, Sephadex G-100, and concanavalin A Sepharose column chromatography. Two or three types of polyphenol oxidase were separated on concanavalin A Sepharose. Type I and II polyphenol oxidases did not bind to concanavalin A Sepharose. Type I seemed to be an aggregated form of polyphenol oxidase. Type III polyphenol oxidase, which is presumed to be glycosylated because it was bound to concanavalin A Sepharose and eluted with $\alpha$-D-methyl glucopyranoside, was further purified by chromatography on Econo-Pac Q and Superose 12. Glycosylated polyphenol oxidase was purified 130-fold from the dissolved ammonium sulfate pellet resulting in about $6\;{\mu}g$ of the enzyme from 100 g of potato tuber periderm. The molecular weight of the glycosylated enzyme determined by SDS-polyacrylamide gel electrophoresis was about 64,000. Optimum temperature and pH of both II and type III potato polyphenol oxidases were $20^{\circ}C$ and pH 7.0, respectively. Glycosylated form of polyphenol oxidase (type III) preferred catechol to catechin as a substrate, whereas type II enzyme showed the reverse substrate preference.