Enzymatic Reaction (image will open in a new window) Polyphenol
oxidase (tyrosinase) (TY) is a bifunctional, copper-containing
oxidase having both catecholase and cresolase activity
(Malmström and Rydén 1968): Jolley et al. (1974) refer to it as
an oxygen and 4 electron-transferring phenol oxidase. It is
responsible for browning reactions throughout the phylogenetic
scale. Although a tyrosinase from Neurospora crassa has been
purified (Fling et al. 1963), most work has been done with the
mushroom enzyme, even though yields and consistency are poor;
its multiplicity was shown by Smith and Krueger (1962).
Bouchilloux et al. (1963) obtained four enzymes. See review by
Nelson and Mason (1970). Characteristics of Polyphenol Oxidase
from Mushroom: Molecular weight: 128,000 (Duckworth and Coleman
1970). Composition: The enzyme is a tetramer containing four
gram atoms of copper per molecule (Jolley et al. 1974), and two
binding sites for aromatic compounds including phenolic
substrates. There is also a distinctly dif