Phenoloxidases of perennial plants: Hydroxylase activity, isolation and physiological role

The difficulties of isolation of phenoloxidases with hydroxylase activity from different plants have been discussed. Phenoloxidase with high hydroxylase activity has been isolated from tea and kivi leaves, apple (Kekhura) fruits, walnut husks and vine stems. The tea leaf phenoloxidase has been shown to be able to catalyze the hydoxylation of the natural substrate p-coumaric acid. The step in the secondary metabolism in which phenoloxidase hydroxylase activity may be included in the plant lignification process has been shown. It has been supposed that masking of hydroxylase activity of phenoloxidase might be connected with the difficulties and peculiarities of the enzyme isolation and perhaps, hydroxylase activity of perennial plant phenoloxidase is included in the process of lignin formation.