Kinetic characterization of tyrosinase containing mushroom (Agaricus bisporus) cells immobilized in silica alginate

• Reaction kinetics of tyrosinase in immobilized mushroom cells was characterized.
• The immobilized cells showed activity between pH 3 and pH 11.
• The observed reaction rate was not limited by the substrate diffusion rate.
• A kinetic model for the catalyzed reaction has been developed.
• The model was suitable to predict the reaction progress under different conditions.

A tyrosinase containing cell preparation from the edible mushroom Agaricus bisporus was immobilized in silica alginate matrix capsules. This catalyst system was characterized in terms of its reaction kinetics using the orthohydroxylation of bisphenol A (BPA) as a model system. The effect of BPA concentration on the reaction rate could be described with the Michaelis–Menten kinetics with an apparent Michaelis–Menten constant of Km = 50.4 μmol/l. The reaction rate was proportional to the immobilized cell concentration in the investigated range. The highest observed apparent maximal reaction rate vmax related to the wet weight of matrix capsules at 30 °C was 51.5 nmol/(min g)). The diffusion coefficient D of BPA within the matrix capsules was determined to 4.9 × 10−10 m2/s ±10% at 30 °C. The studies revealed that the observed reaction rate was not limited by the BPA diffusion rate in the matrix material. The immobilized cells exhibited tyrosinase activity over the whole examined pH range (pH 3–11) with a broad maximum between pH 6 and pH 10. The apparent activation energy EA for the BPA conversion was determined to 37.6 kJ/mol, whereas the apparent activation energy EA,inact for the thermal inactivation of the catalyst was determined to 71.7 kJ/mol. It was demonstrated that the determined parameter values were suitable to predict the change of the BPA concentration with respect to time under different reaction conditions and therefore could be useful for future applications of the catalyst, for example in synthesis of o-diphenols or bioremediation processes.

Figure optionsDownload as PowerPoint slide