Properties of tobacco polyphenol oxidase

Abstract The properties of partially purified tobacco leaf polyphenol oxidase have been studied. Evidence is presented to establish that the observed oxidations of catechol, caffeic acid, and chlorogenic acid were, in fact, catalyzed by polyphenol oxidase. Enzyme stability, activation, x-ray inactivation, inhibition, pH optima, substrate specificity, and substrate affinities are discussed. The properties of the tobacco enzyme do not parallel those of the well-characterized potato and mushroom polyphenol oxidases. The fractionation of leaf extracts has resulted in the concentration of a caffeic-chlorogenic acid specific oxidase; this system is completely free of catechol oxidase activity. Thus, tobacco leaf polyphenol oxidase is at least two enzymes. Of particular interest is the observation that the caffeic-chlorogenic acid oxidase is strongly inhibited by catechol.