Pectin methylesterase from Kiwi and Kaki fruits: purification, characterization and role of pH in the enzyme regulation and interaction with the Kiwi proteinaceous inhibitor

Pectin methylesterase was purified from kiwi (Actinidia chinensis) and kaki fruit ( Diospyros kaki). The pH values of the fruit homogenates were 3.5 and 6.2, respectively. The kiwi enzyme is localized in the cell wall and has a neutral-alkaline pI, whereas the kaki enzyme is localized in the soluble fraction and has a neutral-acidic pI. The molecular weights of the kiwi and kaki enzymes were 50 and 37 kDa, respectively. The two enzymes showed a similar salt and pH dependence of activity, and a different pH dependence of the inhibition by the kiwi proteinaceous inhibitor.