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 first-order kinetics model. Kinetic parameters E_a and Z_T indicated that mPPO had less dependence on temperature and higher heat tolerance than sPPO.