Abstract:
Polyphenoloxidase (PPO) is a nuclear- coded protein that can be found in plastid. PPO
is one of the main enzymes responsible for quality loss due to phenolic degradation
and oxidizes o-diphenolic compounds to the corresponding o-quinones in the presence
of oxygen. The activity of PPO was examined on Bruguiera cy/indrica and B.
sexangula leaves. The effect of different pH (5.8, 6.4 and 8.0) of extraction buffer and
different substrate specificity on PPO activity was investigated. PPO activity was
highest in leaves number one for both species. PPO activity in B.cylindrica was higher
compared with B. sexangula. B. cylindrica shown highest activity in pH 8.0 and B.
sexangula was in pH 5.8. The enzyme seemed to have the highest affinity which
indicates by lowest Km value with pyragallol for B. cy/indrica and 4-methylcatechol
for B. sexangu/a. The most efficient phenolic substrate for B. cy/indrica and B.
sexangula was 4-methylcatechol by considering the highest ratio VmaxlKm. The species
optimum pH and specific substrates for PPO activity is species dependent. Further
study is needed to characterize the properties and role of PPO in Bruguiera sp.
