以邻苯二酚为底物,采用分光光度法对曹州木瓜多酚氧化酶(PPO)的酶学特性进行了研究。结果表明:曹州木瓜PPO的最适pH为5.0,最适温度为30℃;PPO在60~90℃内的热失活曲线具有双相特征,活化能Ea=112.95 kJ/mol;PPO催化的酶促褐变反应动力学符合米氏方程,且相应动力学参数为K m=6.92 mmol/L,V max=769.23 U;5种抑制剂对PPO的抑制效果从大到小依次为:亚硫酸氢钠>抗坏血酸(Vc)>L-半胱氨酸(Lcys)>柠檬酸>EDTA-2Na;Na+和K+对PPO活性的影响不明显,Al3+、Ba2+、Cu2+对PPO具有抑制作用,Mg2+、Mn2+、Ca2+在低浓度(1 mmol/L)时对PPO具有激活作用,高浓度(10 mmol/L)时具有抑制作用。

Enzymatic characterization of polyphenol oxidase(PPO) from Caozhou Chaenomeles sinensis was determined spectrophometrically using catechol as substrate.The results showed that the optimum pH and temperature for the enzymatic oxidation were 5.0 and 30℃,respectively.Thermal inactivation between 60 and 90℃ was observed to be biphasic with activation energy of 112.95 kJ / mol.The reaction kinetic for PPO-catalyzed browning was in accord with Michaelis-Menten equation,where the Michaelis constant Km and the maximum velocity value Vmax were 6.92 mmol / L and 769.23 U,respectively.NaHSO 3,ascorbic acid,L-cys,citric acid and EDTA-2Na significantly inhibited the PPO activity in the order of NaHSO 3 > ascorbic acid > L-cys > citric acid > EDTA-2Na.Na+and K+had no effect on PPO activity.The decreased PPO activity was observed in presence of Al3 +,Ba2 +and Cu2 +.Mg2 +,Mn2 + and Ca2 +activated PPO at lower concentration(1 mmol / L) while inhibited at higher concentration(10 mmol / L).