Enzymological Characteristics of Polyphenol Oxidase from Hawthorn
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Abstract:
The enzymatic characteirstics of Polyphenol oxidase (PPO) from hawthorn was studied The effects of substrate specificity, pH value, temperature, thermostability, substrate concentration, metal ions, and inhibitors on PPO activity were examined using spectrophotometry . The optimum substrate, pH value, temperature, and substrate concentration for PPO were found to be catechol, 6.5, 40 ℃, and 0.10 mol/L, respectively. PPO was completely inactivated by heating at 90 ℃ for 1.0 min or 85 ℃ for 1.5 min. PPO activity followed Michaelis-Menten kinetics in the enzymatic browning reaction. The Km and Vmax values were 55.83 mmol/L and 98.04 U/min, respectively. Metal ion Al3+ showed relatively strong inhibitory effect on the enzyme activity, followed by Mn2+, Ca2+, and Zn2+, where all four substances showed dose-dependent effect. The inhibitory effects of Cu2+ and Mg2+ on enzyme activity were not obvious, while activity was promoted to some degree by Fe3+. At the same concentration, inhibitory effects were in the following order: ascorbic acid > L-cysteine, NaHSO3 > citric acid, where ascorbic acid showed the most significant inhibitory effect on PPO activity.
