Quantification of polyhenoloxidase (PPO) from Bruguiera cylindria and B. sexabgula

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.