TYROSINASE - KINETIC-ANALYSIS OF THE TRANSIENT PHASE AND THE STEADY-STATE

The transient phase of tyrosinase activity acting on monophenols has b een investigated. Although an analytical solution for the lag period ( tau) cannot be obtained, its dependence on reagent concentration and p H is studied. It is established that decreases as the quantity of enzy me increases, although it increases when monophenol or pH are increase d. The computer simulation shows those rate constants whose variations affect the transient phase most significantly. In addition, the stead y state of the pathway is studied using tyrosinases from several sourc es such as mushroom, frog epidermis and grape. The kinetic analysis, w hich is based on not imposing restrictions on the values of the rate c onstants involved in the mechanism, allows us to obtain analytical exp ressions for both monophenolase and diphenolase activities and explain s the experimental results obtained with the different enzymes. The va lues determined for the kinetic parameter, R, point to the monophenol hydroxylation step as being the limiting step of the turnover, while t he values obtained for n suggest the absence of fast equilibrium in th e oxidation of diphenol by E(met).