The following reaction mixture was employed: 0.02 m
sodium phosphate buffer, 20 mm catechol, 400 lL of
enzyme extract (pH 6.8); total volume 3.0 mL. The
mixture was incubated at 30 C and the enzymatic
activity evaluated by measuring the increase in optical
density (OD) at 410 nm (Serradell et al., 2000). The
enzymatic activity was calculated from the initial slope
of the absorbance vs. time plot activity graph. In all
experiments, control reactions without enzyme were
included and no significant oxidation of catechol was
observed during the measurement of PPO activity. The
enzymatic activity unit (U) was defined as the amount of
enzyme required for an increase of 0.01 OD unit min)1
under test conditions.