Fractional purification and kinetic parameters (Km and Vmax) of polyphenol oxidase extracted from three segments of Solanum melongenas and Musa sapietum fruits

Polyphenol oxidase (PPO) was extracted from three segments of Solanum melongenas and Musa sapietum fruits and partially purified. The specific activity of PPO was measured at each purification step to ascertain level of enzyme purity. In all cases, PPO conformed to Michaelis-Menten kinetics, showing different values of kinetics parameters. Michaelis-Menten constant (PPOKm) of S. melongenas mid-section and anterior segments showed no significant difference (p < 0.05), whereas the posterior gave PPOKm = 4.6±0.49 mM (p > 0.05). Maximum PPO activity (PPOVmax) was highest in the posterior segment: PPOVmax = 0.602±0.09 U. Mid-section of M. sapietum exhibited the highest Km value (PPOKm = 5.8±0.69 mM) compared with the anterior (PPOKm = 3.9±0.69 mM) (p > 0.05) and posterior PPOKm = 4.9±0.11 mM segments (p < 0.05). Overall, M. sapietum PPOKm values were relatively higher than those of S. melongenas. Posterior S. melongenas exhibited the highest PPOVmax = 0.602±0.09 U, whereas the lowest value was registered in the anterior segment of M. sapietum PPOVmax = 0.234±0.09 U. Substrate specificity for PPO (PPOVmax/Km) extracted from various segments of S. melongenas was in the increasing order of Mid-section > Posterior > Anterior, whereas that of M. sapietum was Mid-section > Anterior > Posterior. PPOVmax/Km between the two fruits showed strong positive correlation (r = 0.862339). Catechol was a better substrate for PPOS. melongenas than PPOM. sapietum. The experimentally observed kinetic parameters of S. melongenas and M. sapietum signified the presence of PPO isoenzymes and non-uniform distribution of PPO in the two fruits.