杏鲍菇多酚氧化酶的酶学特性研究

以杏鲍菇中多酚氧化酶（PPO）为研究对象,采用分光光度法在420nm处对其酶学特性进行研究。结果表明,杏鲍菇PPO的最适底物为邻苯二酚;最适pH为6.0;最适温度为35℃;90℃处理2min,可使酶完全失活;PPO催化的酶促褐变反应动力学符合米氏方程,动力学参数为K_m=0.0207mol/L,V_max=41.32U/min;7种金属离子对PPO酶活性的影响效果各不相同,Al³⁺、Mn²⁺对PPO酶活性有一定的抑制作用,Mg²⁺、Zn²⁺、Ca²⁺和Cu²⁺对PPO酶活性的抑制作用不明显,Fe³⁺对PPO酶活性有激活作用;抗坏血酸、柠檬酸、L-半胱氨酸和亚硫酸钠对PPO酶活性的抑制作用均随浓度的增大而加强,抑制能力由强到弱依次为:抗坏血酸>亚硫酸氢钠>L-半胱氨酸>柠檬酸。 

Study on enzymatic characteristics of polyphenol oxidase from Pleurotus eryngii Quel.

The enzymatic characteristics of polyphenol oxidase (PPO) from Pleurotus eryngii Quel.was studied by spectrophotometer at 420nm.The results showed that the optimum substrate for this enzyme was catechol.The PPO enzyme had the highest activity at pH6.0 and 35℃.The enzyme activity would been inactivated completely after exposure to 90℃for 2min.The kinetics of enzyme-catalyzed reaction of PPO was in accord with Michaelis-Menten equation, with K_m and V_max values of 0.0207mol/L and 41.32U/min, respectively.Seven kinds of metal ions had different effects on PPO activity, Al～ (3+) and Mn～ (2+) had an inhibitory effect on the enzyme, while Fe～ (3+) had a stimulative effect on the enzyme, and the effect of Mg～ (2+) , Zn～ (2+) , Ca～ (2+) and Cu～ (2+) on enzyme was not obvious.In the range designated, it was increasing in inhibitory effects of ascorbic acid, citric acid, NaHSO₃ and L-Cysteine against enzyme activity with the increasing concentration, and the order as follow:ascorbic acid﹥NaHSO₃﹥L-cysteine﹥citric acid.