The highest PPO activity
was found for the tri-phenolic compound pyrogallol.
Catecholand 3-methylcatechol showed similar reactivity.
The presence of an additional hydroxyl group, as found in pyrogallol,
therefore enhances PPO activity in contrast to a methyl group or
a hydrogen atom in the same position.
Substrates carrying a carboxylic acid group displayed the lowest PPO activity.
Gallic acid, a tri-phenolic compound, is a superior substrate compared to
protocatechuic acid, a di-phenolic compound.