It is responsible for browning reactions through the phylogenetic scale. The enzyme has a molecular weight of 128,000 daltons. It is a tetramer containing four gram atoms of copper per molecule and two binding sites for aromatic compounds including phenolic substrates. There is a distinct binding site for oxygen. The optimum pH range is 6 - 7.
Polyphenol oxidase is inhibited by compounds that complex with copper.
The enzyme is also inhibited competitively by benzoic acid with respect to catechol and by cyanide with respect to oxygen. The latter is accompanied by an increase in absorbance at 280 nm. The rate of increase is proportional to enzyme concentration and linear during a period of 5 - 10 minutes after an initial lag. The Multiple Forms of Mushroom Tyrosinase. Purification and Molecular Properties of the Enzymes, J. Biol .