title: Fluorescence detection of tyrosinase activity on dopamine-betaxanthin purified from Portulaca oleracea (common purslane) flowers.
abstract: Tyrosinase or polyphenol oxidase (EC 1.14.18.1) is one of the key enzymes for the biosynthesis of natural pigment betalains. These are an important class of water-soluble pigments, characteristic of plants belonging to the order Caryophyllales. In this work, dopamine-betaxanthin (also known as miraxanthin V) is reported as the pigment responsible for the bright coloration in yellow flowers of Portulaca oleracea (common purslane). The natural pigment is purified, and used as a substrate for the catecholase (diphenolase) activity of the enzyme tyrosinase. A new, continuous method to follow the activity is developed based on the fluorescent properties of the betaxanthin. Fluorescence of the enzyme activity derived products is reported for the first time. Relevance of the fluorescent phenomenon is discussed based on fluorescence images and the description of a physiological inner filter effect present in flowers of P. oleracea. The first description of the betalain content in flower pistils is also provided.
authors.affiliation: Departamento de Bioquimica y Biologia Molecular A, Unidad Docente de Biologia, Facultad de Veterinaria, Universidad de Murcia, Espinardo, Murcia, Spain. fgandia@um.es
authors.forename: Fernando
authors.initials: F
authors.lastname: Gandía-Herrero
authors.forename: Mercedes
authors.initials: M
authors.lastname: Jiménez-Atiénzar
authors.forename: Juana
authors.initials: J
authors.lastname: Cabanes
authors.forename: Josefa
authors.initials: J
authors.lastname: Escribano
authors.forename: Francisco
authors.initials: F
authors.lastname: García-Carmona
mesh_terms: D050858:Betalains / Q000032:analysis / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004298:Dopamine / Q000302:isolation & purification / Q000378:metabolism*; D035264:Flowers / Q000737:chemistry*; D005452:Fluoresceins; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D010042:Ouabain / Q000031:analogs & derivatives; D010848:Picolinic Acids / Q000302:isolation & purification / Q000378:metabolism*; D031822:Portulaca / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D005452:Fluoresceins; D010848:Picolinic Acids; C488995:betaxanthin; C109049:rhodol green-ethylenediamine-ouabain; D050858:Betalains; D010042:Ouabain; D014442:Monophenol Monooxygenase; D004298:Dopamine