OXYGEN MICHAELIS CONSTANTS FOR TYROSINASE

The Michaelis constant of tyrosinase for oxygen in the presence of mon ophenols and o-diphenols, which generate a cyclizable o-quinone, has b een 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 ki netic analysis [Rodriguez-Lopez, J. N., Tudela, J., Varon, R., Garcia- Carmona, F. and Garcia-Canovas, F. (1992) J. Biol. Chem. 267, 3801-381 0] a quantitative ratio has been established between the Michaelis con stants for oxygen in the presence of monophenols and their o-diphenols . This ratio is used for the determination of the Michaelis constant f or oxygen with monophenols when its value cannot be calculated experim entally.