(+)-Larreatricin hydroxylase, an enantio-specific polyphenol oxidase from the creosote bush ( Larrea tridentata )

An enantio-specific polyphenol oxidase (PPO) was purified approximately 1,700-fold to apparent homogeneity from the creosote bush (Larrea tridentata), and its encoding gene was cloned. The posttranslationally processed PPO ( approximately 43 kDa) has a central role in the biosynthesis of the creosote bush 8-8' linked lignans, whose representatives, such as nordihydroguaiaretic acid and its congeners, have potent antiviral, anticancer, and antioxidant properties. The PPO primarily engenders the enantio-specific conversion of (+)-larreatricin into (+)-3'-hydroxylarreatricin, with the regiochemistry of catalysis being unambiguously established by different NMR spectroscopic analyses; the corresponding (-)-enantiomer did not serve as a substrate. This enantio-specificity for a PPO, a representative of a widespread class of enzymes, provides additional insight into their actual physiological roles that hitherto have been difficult to determine.