The international nomenclature for the enzymes involved in the browning reaction
has changed. The first enzyme, monophenol monoxygenase or tyrosinase (EC 1.14.18.1),
initiates the browning reaction, which later involves diphenol oxidase or catechol oxidase
(EC 1.10.3.2) and laccase (EC 1.10.3.1). Catecholase oxidase will be referred to as
‘polyphenol oxidase’ (PPO). This enzyme requires the presence of both a copper prosthetic
group and oxygen. The copper is believed to be monovalent in the case of the mushroom
PPO and divalent in the case of the potato enzyme. PPO is classified as an oxidoreductase,
with oxygen functioning as the hydrogen acceptor.