Oxygen Michaelis constants for tyrosinase

Abstract

The Michaelis constant of tyrosinase for oxygen in the presence of monophenols and o-diphenols, which generate a cyclizable o-quinone, has been studied. This constant depends on the nature of the monophenol and o-diphenol and is always lower in the presence of the former than of the latter. From the mechanism proposed for tyrosinase and from its kinetic analysis [Rodríguez-López, J. N., Tudela, J., Varón, R., García-Carmona, F. and García-Cánovas, F. (1992) J. Biol. Chem. 267, 3801-3810] a quantitative ratio has been established between the Michaelis constants for oxygen in the presence of monophenols and their o-diphenols. This ratio is used for the determination of the Michaelis constant for oxygen with monophenols when its value cannot be calculated experimentally.

Screen-printed multienzyme arrays for use in amperometric batch and flow systems

“…In Ref. [33] the marked enhancement of the phenol reduction current of a tyrosinase electrode in the presence of 1.0 mmol L -1 H 2 O 2 was explained by mono-and diphenolase activities of the enzyme which can exist in different states yielding the quinone derivative products [34,35]. The mushroom enzyme predominates in a monophenolase inactive state (met form), being unable to bind oxygen, while the active monophenolase (oxy form), in a fresh preparation, is present in very small proportions [36,37].…”

A Disposable Optrode Using Immobilized Tyrosinase Films

“…The proposed mechanism for the diphenolase activity of tyrosinase has been studied by Rodriguez-López et al (15). In case of dopa oxidation by tyrosinase the process involves the spontaneous cyclization of dopaquinone to give rise to 5,6-dihydroxyindoline (cyclodopa).…”

Modelling the biosensor utilising parallel substrates conversion

“…(5) the initial boundary value problem (5)- (12) can be analytically solved only for a specific set of the model parameters [17,19,24,32]. A uniform discrete grid in both directions (space x and time t) with 600 points in the space direction was introduced to find a numerical solution.…”

“…The analysed biosensor produces molecular oxygen, which can be selectively determined by a sensitive to oxygen electrode, e.g. Clark type electrode [11,12]. For this reason the biosensors using this high selective electrode as a transducer are applicable for metabolites determination in complex biological liquids [13].…”