(pH 6.0) to obtain a homogenate, which was centrifuged at 12,000g
and 4 C for 30 min. To the supernatant, (NH4)2SO4 was added to
obtain 95% saturation, which was then centrifuged at 12,000g
and 4 C for 30 min. The precipitate was dissolved in 5 mL of
10 mM phosphate buffer (pH 6.0) and dialysed against the same
buffer at 4 C for 24 h with four exchanges of buffer. The dialysed
enzyme extract, was used to measure PPO activity in the following
experiments. The protein content in the enzyme extract was determined
according to the method described by Bradford (1976),
using bovine serum albumin as standard