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American Journal of Plant Physiology
Year: 2013  |  Volume: 8  |  Issue: 2  |  Page No.: 84 - 92

Fractional Purification and Kinetic Parameters (Km and Vmax) of Polyphenol Oxidase Extracted from Three Segments of Solanum melongenas and Musa sapientum Fruits

P.C. Chikezie, A.R. Akuwudike, C.M. Chikezie and C.O. Ibegbulem    

Abstract: Largely, kinetic properties of Polyphenol Oxidase (PPO) involved the study of enzyme extracts obtained from whole fruits and vegetables. In the present study, PPO was extracted from three segments of Solanum melongenas and Musa sapientum 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 for PPO (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. sapientum 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. sapientum 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. sapientum 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. sapientum 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. sapientum. The experimentally observed kinetic parameters of S. melongenas and M. sapientum signified the presence of PPO isoenzymes and non-uniform distribution of PPO in the two fruits.

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