Abstract:
Polyphenol oxidases (PPO) are enzymes that catalyze the oxidation of certain phenolic
substrates to quinones in the presence of molecular oxygen. This study was carried to
determine the polyphenoloxidase (PPO) activity in different position of leaves in R.
apiculata and R. mucronata. The PPO activity was also measured when subjected to
different pH of extraction buffer (pH 5.8, 6.4 and 8.0) and different substrate specificity
which are cathecol, pyragallol and 4-methylcathecol. R. mucronata has highest PPO
activity than R. apiculata in all leaf samples. The PPO activity in R. mucronata are
992±22.9 unit/μg proteins and R. apiculata are 968 ± 12.9 unit/μg proteins in old leaves.
The most suitable pH for PPO activity in R. apiculata is pH 8.0 while R. mucronata is pH
5.8. The enzyme seemed to have the highest affinity (lowest Km value) for cathecol for R.
mucronata and 4-methylcathecol for R. apiculata. Hence, from the Vmax/Km values, 4-
methycathecol is preferred phenolic substrate for R. apiculata and R. mucronata is
cathecol. Further study is required to determine the characterization the PPO in
Rhizophoraceae sp.
