S. cyaneus (♦) and T. versicolor (▲) laccase residual activity as a function of incubation time at different pH in buffer solution at 25°C. Plots show the average and values of duplicates. Relative activity refers to the maximum activity measured during the test. The initial laccase activity was 130 U l-1 in all the tests. Lines: bi-exponential inactivation model fitted to the data. The white symbols (◊) represent S. cyaneus laccase residual activity in the tests where the pH increased gradually to 7.3-7.7 due to microbial growth. Due to change in pH, these data were not used to fit the model. The insert at pH 6 shows the increase of T. versicolor laccase activity during the first days of incubation, also observed at pH 5, 7 and 8.