Studies on Purified Polyphenol Oxidase from Red Cocoyam (Xanthosomamafafa)

Abstract

Polyphenol oxidase (PPO) catalyzes oxidative conversion of phenolic substrates to their respective quinones, which further polymerize to form macromolecules resulting to browning reactions in various organisms. Here, the presence, purification and physicochemical properties of PPO from Xanthosomamafafa are described. Polyphenol oxidase from X. mafafa (xmPPO) is purified using a combination of ion-exchange (cation and anion exchanger) and gel filtration chromatography. The enzyme appeared to be homodimeric. The subunit molecular weight obtained on SDS-PAGE was 24.5 ± 0.3 kDa while that of native molecular weight on Sephadex G-100 was 44.3 ± 1.8 kDa. The Km and Vmax obtained for the purified xmPPO using L-DOPA as substrate were 6.5 ± 1.0 mM and 35.4 ± 2.0 units/mg protein respectively leading to first–order rate constant (kcat/Km) value of 3.9 × 10³ s^-1 M^-1. The optimum pH and temperature for the purified enzyme were 6.5 and 50 oC respectively. The enzyme was stable to heat at up to 60 ^oC retaining close to 70% residual activity. Substrates specificity revealed the enzyme had both monophenolase and diphenolase activities. In conclusion, the combination of properties of PPO from X. mafafa revealed that, it could also be enzyme of interest in several biotechnological applications.