The use of PAMAM dendrimers as a platform for laccase immobilization: kinetic characterization of the enzyme.

The kinetic behavior of the enzyme laccase in solution and immobilized onto carbon platforms using poly(amido amine) (PAMAM) dendrimers has been investigated. The results with the immobilized enzymes have demonstrated that almost ten times more enzyme on the carbon support is required for satisfactory kinetic rates to be achieved. Furthermore, the study as a function of the substrate concentration revealed that the kinetic behavior of the enzyme in solution fits the Michaelis-Menten model. However, when the enzyme is immobilized onto the carbon surface, the catalyzed reaction follows a particular kinetic behavior with apparent positive cooperativity. The highest activity with laccase (in solution or immobilized) is achieved around pH 4.5, and the substrate conversion rate clearly diminishes with rising pH. The optimum temperature lies around 60 °C. The enzyme displays good catalytic activity in a wide range of pH and temperature values. The stability tests evidenced that there is no appreciable reduction in the enzymatic activity after immobilization within the first 30 days. Taking into account both the kinetic and stability tests, one can infer that the use of PAMAM dendrimers seems to be a very attractive approach for the immobilization of enzymes, as well as a feasible and useful methodology for the anchoring of enzymes with potential application in many biotechnological areas.