Characterization of polyphenol oxidase from Uapaca kirkiana fruit

Abstract

Polyphenol oxidase (PPO), the enzyme responsible for the postharvest spoilage of fruits, was extracted and purified from Uapaca kirkiana peel and pulp by ammonium sulfate precipitation and dialysis. Further purification of peel PPO was carried out by gel filtration chromatography. Optimum pH values were 7 and 8 for peel and pulp PPO, respectively. The optimum temperatures for peel and pulp PPO were 45 and 35 • C, respectively. Inhibition studies of the PPO enzyme were performed using citric acid, sodium azide, sodium metabisulfite and thiourea. The most effective inhibitors were sodium azide and citric acid for both peel and pulp PPO. V max and K m values were 13.63 units min −1 and 4.923 mmol L −1 , respectively, for peel PPO and 14.03 units min −1 and 5.43 mmol L −1 , respectively, for pulp PPO. Three isoenzymes of Uapaca kirkiana PPO were detected by polyacrylamide gel electrophoresis. One of the isoenzymes could be identified as having a molecular weight of 26 625 Da.

Polyphenol oxidases in plants and fungi: Going places? A review

“…The latter has been partially purified and appears to be an example of a PPO in the Cruciferae. Annona muricata (Bora et al, 2004), oregano (Dogan et al, 2005a), persimmon (Ozen et al, 2004), artichoke (Dogan et al, 2005b), marula (Sclerocarya birrea) (Mduli, 2005), loquat (Eriobotrya japonica) (Sellés-Marchart et al, 2006) and Uapaca kikiana fruit, a plant belonging to the Euphoriaceae (Muchuweti et al, 2006), all contain PPO. The PPO level in apricot fruits remains high even at a stage when it's mRNA can no longer be detected, indicating that the protein is stable for long periods (Chevalier et al, 1999).…”

Some kinetic properties of polyphenol oxidase obtained from dill (Anethum graveolens)

“…The reaction was carried out at various temperatures and pH values with the substrates mentioned below. PPO activity was calculated from the linear part of the curve giving absorbance values at 420 nm versus time [37,38,39,40]. One unit of PPO activity (EU/mL.min) was defined as the amount of enzyme that caused an increase in absorbance of 0.001/min [41,42].…”