67.8ku丝瓜多酚氧化酶酶学性质的研究

目的:为对67.8ku丝瓜多酚氧化酶（PPO）的酶学性质进行研究。方法:从丝瓜中提取、纯化得67.8ku的丝瓜多酚氧化酶,并分别从温度、pH、作用底物、金属离子、抑制剂及表面活性剂对丝瓜PPO活性的影响等方面对丝瓜PPO的酶学性质进行研究。结果:结果表明,pH为6.0时相对酶活最高,pH3.0⁸.0酶活较稳定;其最适作用温度为30℃,对热稳定性较强,70℃保温120min后还具有40%的相对酶活;Co2+、K+、Ca2+等对酶有较强的激活作用,而Na+、Mg2+、Cu2+对酶有明显的抑制作用;抗坏血酸为该酶最好的抑制剂,其次为半胱氨酸、β-巯基乙醇、Na2S2O3、Na2SO3等;十二烷基肌氨酸钠（Laurouyl Sarcosine）、十二烷基硫酸钠（SDS）等对酶有一定的激活作用,而十六烷基三甲基溴化铵（CTAB）、吐温-20（Tween-20）对酶有抑制作用;与l-多巴（l-dopa）的结合力最强,以其为底物时该酶的Km为1.32mmol/L,Vmax为0.22OD475/min。结论:该研究确定了丝瓜多酚氧化酶的最适作用条件及其影响因素,可为控制丝瓜在贮藏、加工过程中的酶促褐变提供理论依据。 

Study on enzymatic properties of 67.8ku polyphenol oxidase in loofah

Objective:To study the enzymatic properties of 67.8ku PPO in loofah. Methods:Polyphenol oxidase of 67.8ku was extracted and purified from loofah and the effect of tempere, pH, substrats, metal ions, inhibitors and surfactants on PPO activity were researched respectively. Results:The enzyme activity was the strongest when pH value was 6.0 and its activity was stable in pH3.0⁸.0. The optimum temperature of PPO was 30℃ and its thermostability was good. After 120min of keeping 70℃, its relative activity was 40%. The enzyme was activated by Co2+, K+and Ca2+, but inhibited by Na+, Mg2+and Cu2+. Ascorbic acid was the best inhibitor of the PPO, followed by cysteine, β-Mercaptoethanol, sodium thiosulfate and sodium sulfite. Some surfactants had significant stimulation to the enzyme activity such as Laurouyl Sarcosine and SDS, but some had inhibiton such as CTAB and Tween-20. The binding ability of l-dopa with the enzyme was the strongest, taking it as substrate, the value of Km and Vmax of PPO were 1.32mmol/L and 0.22OD475 /min respectively. Conclusion:The study identified the optimum conditions and the critical factors affected its activity of PPO in loofah, it could provide theoretical basis for the prevention of enzymatic browning during storage and processing of the loofah.