砀山酥梨膜结合态与可溶态多酚氧化酶性质比较

为探究砀山酥梨膜结合态多酚氧化酶（mPPO）性质，本文以砀山酥梨为原料，研究其mPPO催化特性及热失活动力学，并与可溶态多酚氧化酶（sPPO）性质进行比较。结果表明:以邻苯二酚为底物时，mPPO与sPPO催化特性及热失活动力学性质不同。mPPO比活力及对底物亲和力高于sPPO。mPPO在pH4.50时酶活最高，而sPPO最适pH为5.00。mPPO酸碱稳定性高于sPPO，mPPO在pH3.50～4.50环境中保持24 h后酶活大于原始酶活。砀山酥梨mPPO在35～45 ℃温度区间内活性最高，且mPPO在55～75 ℃区间热稳定性高于sPPO。热失活动力学分析结果表明，热处理对sPPO及mPPO的钝化均符合一级反应动力学，动力学参数E_a值及Z_T值分析表明mPPO比sPPO催化反应对温度的依赖性更小，热耐受性更高。

Comparison of Properties of Membrane-Bound and Soluble Polyphenol Oxidase from Dangshan Pear

In order to study the properties of membrane-bound polyphenol oxidase(mPPO)from Dangshan pear,the catalytic characteristics and thermal inactivation kinetics of mPPO from Dangshan pear were studied.Properties of mPPO were also compared with those of soluble polyphenol oxidase(sPPO).Results showed that,when catechol was used as substrate,the catalytic properties and thermal deactivation mechanical properties of mPPO and sPPO were quite different.The activity of mPPO had a stronger affinity to the substrate than sPPO with catechol as the substrate.The optimal pH of mPPO and sPPO was pH4.50 and 5.00,respectively.The pH stability of mPPO was higher than that of sPPO,and the residual enzyme activity of mPPO at pH3.50~4.50 for 24 h was higher than that of the original enzyme activity.The optimum reaction temperature for mPPO was 35~45℃and mPPO had higher thermal stability than sPPO at 55~75℃.The kinetic analysis of thermal deactivation showed that the passivation of sPPO and mPPO was in accordance with the firstorder kinetics model.Kinetic parameters Ea and ZT indicated that mPPO had less dependence on temperature and higher heat tolerance than sPPO.