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Polyphenoloxidase from Riesling and Dornfelder wine grapes (Vitis vinifera) is a tyrosinase

Fronk, Petra, Hartmann, Hermann, Bauer, Margarita, Solem, Even, Jaenicke, Elmar, Tenzer, Stefan, Decker, Heinz
Food chemistry 2015 v.183 pp. 49-57
Vitis vinifera, active sites, catechol oxidase, gel chromatography, oxidation, polyacrylamide gel electrophoresis, quinones, ultracentrifugation, wine grapes
Polyphenoloxidases (PPO) of the type-3 copper protein family are considered to be catecholoxidases catalyzing the oxidation of o-diphenols to their corresponding quinones. PPO from Grenache grapes has recently been reported to display only diphenolase activity. In contrast, we have characterized PPOs from Dornfelder and Riesling grapes which display both monophenolase and diphenolase activity. Ultracentrifugation and size exclusion chromatography indicated that both PPOs occur as monomers with Mr of about 38kDa. Non-reducing SDS–PAGE shows two bands of about 38kDa exhibiting strong activity. Remarkably, three bands up to 60kDa displayed only very weak PPO activity, supporting the hypothesis that the C-terminal domain covers the entrance to the active site. Molecular dynamic analysis indicated that the hydroxyl group of monophenolic substrates can bind to CuA after the flexible but sterically hindering Phe 259 swings away on a picosecond time scale.