Acid phosphatase activity was routinely assayed, at least
in duplicate, by incubating the enzyme with p-nitrophenylphosphate
(p-NPP) as substrate, as previously described
(Prazeres et al., 2004). The enzyme activity was determined
in a final volume of 1 ml containing 0.1 M sodium acetate
buffer pH 5.0, and 10 mM substrate. The reaction system
was incubated for 40 min at 37 C and the reaction was terminated
by addition of 1 ml of 1 M NaOH. The p-nitrophenol
(p-NP) released was measured at 405 nm in a
UNICAM 8625 UV/VIS spectrophotometer. The amount
of p-NP produced was calculated using a molar extinction
coefficient of 18 300 M1 cm1.