title: Catalysis and inactivation of tyrosinase in its action on hydroxyhydroquinone.
abstract: Hydroxyhydroquinone (HHQ) was characterized kinetically as a tyrosinase substrate. A kinetic mechanism is proposed, in which HHQ is considered as a monophenol or as an o-diphenol, depending on the part of the molecule that interacts with the enzyme. The kinetic parameters obtained from an analysis of the measurements of the initial steady state rate of 2-hydroxy p-benzoquinone formation were kcatapp=229.0±7.7 s(-1) and KMapp,HHQ=0.40±0.05 mM. Furthermore, the action of tyrosinase on HHQ led to the enzyme's inactivation through a suicide inactivation mechanism. This suicide inactivation process was characterized kinetically by λmaxapp (the apparent maximum inactivation constant) and r, the number of turnovers made by 1 mol of enzyme before being inactivated. The values of λmaxapp and r were (8.2±0.1)×10(-3) s(-1) and 35,740±2,548, respectively.
authors.affiliation: GENZ: Grupo de Investigación de Enzimología, Departamento de Bioquímica y Biología Molecular-A, Facultad de Biología, Campus de Excelencia Internacional "Mare Nostrum", Universidad de Murcia, Espinardo, Murcia, E-30100, Spain.
authors.forename: Maria
authors.initials: M
authors.lastname: del Mar Garcia-Molina
authors.forename: Jose Luis
authors.initials: JL
authors.lastname: Muñoz-Muñoz
authors.forename: Jose
authors.initials: J
authors.lastname: Berna
authors.forename: Pedro Antonio
authors.initials: PA
authors.lastname: García-Ruiz
authors.forename: Jose Neptuno
authors.initials: JN
authors.lastname: Rodriguez-Lopez
authors.forename: Francisco
authors.initials: F
authors.lastname: Garcia-Canovas
mesh_terms: D000363:Agaricales / Q000201:enzymology; D002384:Catalysis; D004156:Catechol Oxidase / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006873:Hydroquinones / Q000378:metabolism*; D007700:Kinetics; D014442:Monophenol Monooxygenase / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D010636:Phenols
chemical_list: D006873:Hydroquinones; D010636:Phenols; C013038:hydroxyhydroquinone; D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase; C031927:hydroquinone
keywords: catalysis; hydroquinone; hydroxyhydroquinone; suicide inactivation; tyrosinase