title: A continuous spectrophotometric method for determining the monophenolase and diphenolase activities of apple polyphenol oxidase.
abstract: A continuous spectrophotometric method for the determination of the monophenolase and diphenolase activities of apple polyphenol oxidase is described. The method is based on the coupling reaction between 3-methyl-2-benzothiazolinone hydrazone (MBTH) and the quinone product of the oxidation of p-hydroxyphenyl propionic acid and 3,4-dihydroxyphenyl propionic acid in the presence of polyphenol oxidase. The lambda(max) and molar absorptivity (epsilon) for the MBTH-quinone adduct have been calculated. The presence of MBTH in the reaction medium decreases the lag period during the expression of monophenolase activity. The high value of V(mas) suggests the existence of a high catalytic constant. This, together with the value of epsilon for the MBTH-quinone adduct, makes this method more sensitive than other continuous methods.
authors.affiliation: Departamento de Bioquímica y Biología Molecular-A, Facultad de Biología, Universidad de Murcia, Spain.
authors.forename: J C
authors.initials: JC
authors.lastname: Espín
authors.forename: M
authors.initials: M
authors.lastname: Morales
authors.forename: R
authors.initials: R
authors.lastname: Varón
authors.forename: J
authors.initials: J
authors.lastname: Tudela
authors.forename: F
authors.initials: F
authors.lastname: García-Cánovas
mesh_terms: D004156:Catechol Oxidase / Q000032:analysis*; D004789:Enzyme Activation; D005638:Fruit / Q000201:enzymology*; D013053:Spectrophotometry / Q000379:methods
chemical_list: D004156:Catechol Oxidase