Catalysis and inactivation of tyrosinase in its action on hydroxyhydroquinone

Hydroxyhydroquinone (HHQ) was characterized kinetically as a tyrosinase substrate. A kinetic mechanism is proposed, in which HHQ is considered as a monophenol or as an o ‐diphenol, depending on the part of the molecule that interacts with the enzyme. The kinetic parameters obtained from an analysis of the measurements of the initial steady state rate of 2‐hydroxy p ‐benzoquinone formation werek cat app= 229.0 ± 7.7 s −1 andK M app , HHQ= 0.40 ± 0.05 mM. Furthermore, the action of tyrosinase on HHQ led to the enzyme's inactivation through a suicide inactivation mechanism. This suicide inactivation process was characterized kinetically byλ max app(the apparent maximum inactivation constant) and r , the number of turnovers made by 1 mol of enzyme before being inactivated. The values ofλ max appand r were (8.2 ± 0.1) × 10 −3 s −1 and 35,740 ± 2,548, respectively. © 2014 IUBMB Life, 66(2):122–127, 2014