title: Characterization of the activity of tyrosinase on betaxanthins derived from (R)-amino acids.
abstract: The activity of tyrosinase (EC 1.14.18.1) on selected (R)-betaxanthins is characterized in depth, demonstrating that the activity of the enzyme is not restricted to betaxanthins derived from (S)-amino acids. Conversion of (R)-tyrosine-betaxanthin [(R)-portulacaxanthin II] to the pigment (R)-dopaxanthin and its further oxidation to a series of products is described. Compound identity was studied by high performance liquid chromatography and electrospray ionization-mass spectrometry. The reaction rate on the (R)-isomer of dopaxanthin is 1.9-fold lower than that obtained for the (S)-isomer in previous studies. Tyrosinase showed stereospecificity in its affinity toward betaxanthins. The characterization of the activity of tyrosinase on (R)-betaxanthins reinforces the role of the enzyme in the biosynthetic scheme of betalains.
authors.affiliation: Departamento de Bioquímica y Biología Molecular A, Facultad de Veterinaria, Universidad de Murcia, E-30100 Espinardo, Murcia, Spain.
authors.forename: Fernando
authors.initials: F
authors.lastname: Gandía-Herrero
authors.forename: Josefa
authors.initials: J
authors.lastname: Escribano
authors.forename: Francisco
authors.initials: F
authors.lastname: García-Carmona
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D050858:Betalains / Q000378:metabolism; D050860:Betaxanthins / Q000737:chemistry* / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D007700:Kinetics; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D021241:Spectrometry, Mass, Electrospray Ionization; D013237:Stereoisomerism; D013379:Substrate Specificity
chemical_list: D000596:Amino Acids; D050860:Betaxanthins; D050858:Betalains; D014442:Monophenol Monooxygenase