title: A kinetic study of p-cresol oxidation by quince fruit polyphenol oxidase.
abstract: The monophenolase activity of quince pulp polyphenol oxidase was characterized by extracting samples using a combination of a two-phase partition step in Triton X-114, followed by a PEG 8000/phosphate partition step, and a final ammonium sulfate fractionation between 30 and 75%. The purification method avoids the loss of cresolase activity described in another quince pulp polyphenol oxidase. The activity was characterized by a lag period, whose duration depended on the substrate concentration, the pH, and the presence of catalytic amounts of o-diphenol. By increasing the concentration of o-diphenols, it was possible to evaluate the enzyme activation constant, K(act), which showed a value of 4.5 microM for 4-methylcatechol. A general kinetic mechanism for this enzyme is used to explain the loss of activity that normally occurs during quince pulp polyphenol oxidase purification.
authors.affiliation: Department of Biochemistry and Molecular Biology-A, Faculty of Biology, University of Murcia, Campus Espinardo, E-30071 MURCIA, Spain.
authors.forename: Esteban
authors.initials: E
authors.lastname: Orenes-Piñero
authors.forename: Francisco
authors.initials: F
authors.lastname: García-Carmona
authors.forename: Alvaro
authors.initials: A
authors.lastname: Sánchez-Ferrer
mesh_terms: D004156:Catechol Oxidase / Q000378:metabolism*; D003408:Cresols / Q000378:metabolism*; D005638:Fruit / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D010636:Phenols / Q000494:pharmacology; D027824:Rosaceae / Q000201:enzymology*
chemical_list: D003408:Cresols; D010636:Phenols; C032538:4-cresol; D004156:Catechol Oxidase