Characterization of the activity of tyrosinase on betanidin.
Betalains are an important class of water-soluble pigments, with radical scavenging capacity, which is characteristic of the order Caryophyllales. The structural unit of the violet betacyanins, betanidin is reported as a substrate for the enzyme tyrosinase (EC 1.14.18.1), which plays a key role in the betalains biosynthetic scheme. The compound was identified in Lampranthus productus violet flowers, from which it was extracted and purified. The tyrosinase-mediated oxidation of betanidin was characterized in depth and followed by high-performance liquid chromatography and spectrophotometry. The addition of ascorbic acid reversed the reaction product, betanidin-quinone, to the original pigment. Kinetic analysis revealed a Km = 0.66 mM. Betanidin degradation kinetics was also studied in the absence of the enzyme and demonstrated that pH values over 6.0 and high ionic strength reduce the pigment stability.
Gandía-Herrero
Fernando
F
Departamento de Bioquímica y Biología Molecular A, Unidad Docente de Biología, Facultad de Veterinaria, Universidad de Murcia, E-30100 Espinardo, Murcia, Spain.
Escribano
Josefa
J
García-Carmona
Francisco
F
D001205:Ascorbic Acid / Q000494:pharmacology; D050859:Betacyanins / Q000302:isolation & purification / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D035264:Flowers / Q000737:chemistry; D007700:Kinetics; D019684:Magnoliopsida / Q000737:chemistry; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D013053:Spectrophotometry
D050859:Betacyanins; D014442:Monophenol Monooxygenase; D001205:Ascorbic Acid