title: Kinetic study of the transient phase of a chemical reaction system coupled to an enzymatically catalyzed step. Application to the oxidation of epinine by tyrosinase.
abstract: The present work deals with epinine oxidation by mushroom tyrosinase and sodium metaperiodate. Intermediates produced within short reaction times were characterized by repetitive scanning spectrophotometry and the stoichiometry of the appearance of the respective aminochrome was established. The oxidation pathway from epinine to aminochrome had the following steps: epinine----o-quinone-H+----o-quinone----leukoaminochrome----aminoc hrome. The stoichiometry for the conversion of o-quinone-H+ into the aminochrome of epinine followed the equation: 2 o-quinone-H+----epinine+aminochrome. A transient phase kinetic study has been developed for the system of chemical reactions coupled to an enzymatically catalyzed step, these taking place when epinine is oxidized by mushroom tyrosinase. Rate constants for the implied chemical steps at different temperature and pH values were calculated from analysis of the progress curves of aminochrome accumulation with time. The thermodynamic activation parameters of the chemical steps were also calculated.
mesh_terms: D001487:Basidiomycota / Q000201:enzymology; D004156:Catechol Oxidase / Q000378:metabolism*; D003846:Deoxyepinephrine / Q000378:metabolism*; D004298:Dopamine / Q000031:analogs & derivatives*; D007700:Kinetics; D008433:Mathematics; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D013053:Spectrophotometry
chemical_list: D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase; D003846:Deoxyepinephrine; D004298:Dopamine