Browsing by Subject "Polyphenol oxidase"

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    A continuous spectrophotometric assay for determination of the aureusidin synthase activity of tyrosinase
    (Wiley, 2010-04-13) Jiménez-Atiénzar, Mercedes; Cabanes Cos, Juana; Escribano Cebrián, Josefa; Gandía Herrero, Fernando; Pérez Gilabert, Manuela; García Carmona, Francisco; Departamento de Bioquímica y Biología Molecular "A"
    Introduction – Aurones (aureusidin glycosides) are plant flavonoids that provide yellow colour to the flowers of some orna-mental plants. In this study we analyse the capacity of tyrosinase to catalyse the synthesis of aureusidin by tyrosinase fromthe chalcone THC (2′,4′,6′,4–tetrahydroxychalcone).Objective – To develop a simple continuous spectrophotometric assay for the analysis of the spectrophotometric and kineticcharacteristics of THC oxidation by tyrosinase.Methodology – THC oxidation was routinely assayed by measuring the increase in absorbance at 415 nm vs. reaction time.Results – According to the mechanism proposed for tyrosinase, the enzymatic reaction involves the o-hydroxylation of themonophenol THC to the o-diphenol (PHC, 2′,4′,6′,3,4 – pentahydroxychalcone), which is then oxidised to the correspondingo-quinone in a second enzymatic step. This product is highly unstable and thus undergoes a series of fast chemical reactionsto produce aureusidin. In these experimental conditions, the optimum pH for THC oxidation is 4.5. The progress curvesobtained for THC oxidation showed the appearance of a lag period. The following kinetic parameters were also determined:Km = 0.12 mM , Vm = 13 mM /min, Vm/Km = 0.11/min.Conclusion – This method has made it possible to analyse the spectrophotometric and kinetic characteristics of THC by tyro-sinase. This procedure has the advantages of a short analysis time, straightforward measurement techniques and repro-ducibility. In addition, it also allows the study of tyrosinase inhibitors, such as tropolone.
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    Cinética de hidroxilación y oxidación de compuestos fenólicos por Polifenol Oxidasa de uva Monastrell (Vitis Vinifera)
    (Murcia: Universidad de Murcia, Servicio de Publicaciones, 1987) Sánchez Ferrer, Álvaro; Cabanes Cos, Juana; Bru Martínez, Roque; Facultad de Biología
    La enzima polifenol oxidasa ha sido purificada a partir de uva Monastrell mostrando actividad tanto en la oxidación de monofenoles (cresolasa) como en la de o-difenoles (catecolasa). Los parámetros cinéticos, Km y temperatura óptima, han sido evaluados en ambas actividades. La actividad cresolasa presenta un período de retardo característico, que puede ser modificado por la temperatura, la concentración de enzima, la presencia de o-difenoles y la concentración de sustrato.