title: Detection and characterization of p-coumaric acid hydroxylase in mung bean, Vigna mungo, seedlings.
abstract: A new p-coumaric acid (4-hydroxycinnamic acid) hydroxylase was detected in mung bean seedlings treated with tentoxin, a fungal toxin, in which polyphenol oxidase that hydroxylates a wide variety of monophenols in vitro was completely eliminated. The enzyme required molecular oxygen and showed a pH optimum of 5.0. The enzyme acted only on p-coumaric acid (Km, 3.0 X 10(-5) M), while its specificity for the electron donor was rather broad. The Km value for NADPH (1.5 X 10(-4) M) was much lower than that for L-ascorbic acid (1.0 X 10(-2) M), although the Vmax value was almost the same with both electron donors. The enzyme was potently inhibited by beta-mercaptoethanol (Ki, 3.5 X 10(-6) M) and diethyldithiocarbamate (Ki, 2.3 X 10(-4) M), but was insensitive to p-chloromercuribenzoate. The enzyme was localized in the cell organelles which sedimented between mitochondria and endplasmic reticulum on sucrose density gradient centrifugation. The enzyme activity in the seedling was changed in response to induction by light in a manner suggesting its involvement in biosynthesis of phenolic compounds in mung bean seedlings.
authors.affiliation: Institute for Biochemical Regulation, Faculty of Agriculture, Nagoya University, Aichi.
authors.forename: M
authors.initials: M
authors.lastname: Kojima
authors.forename: W
authors.initials: W
authors.lastname: Takeuchi
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases; D004156:Catechol Oxidase / Q000032:analysis; D002499:Centrifugation, Density Gradient; D065637:Cytochrome P-450 CYP2A6; D003577:Cytochrome P-450 Enzyme System / Q000032:analysis; D007887:Fabaceae / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D006899:Mixed Function Oxygenases / Q000032:analysis*; D010456:Peptides, Cyclic / Q000494:pharmacology; D010636:Phenols / Q000378:metabolism; D010650:Phenylalanine Ammonia-Lyase / Q000032:analysis; D010944:Plants / Q000201:enzymology; D010946:Plants, Medicinal; D013379:Substrate Specificity; D050564:Trans-Cinnamate 4-Monooxygenase
chemical_list: D010456:Peptides, Cyclic; D010636:Phenols; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D004156:Catechol Oxidase; D001189:Aryl Hydrocarbon Hydroxylases; D065637:Cytochrome P-450 CYP2A6; D050564:Trans-Cinnamate 4-Monooxygenase; D010650:Phenylalanine Ammonia-Lyase; C003384:tentoxin