There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Tyrosinase is an enzyme widely distributed in the biosphere. It is one of a group
of proteins with a strongly conserved bicopper active centre able to bind molecular
oxygen. Tyrosinase manifests two catalytic properties; monooxygenase and oxidase activity.
These actions reflect the oxidation states of the active centre. Tyrosinase has four
possible oxidation states and the details of their interaction are shown to give rise
to the unusual kinetic behaviour of the enzyme. The resting state of the enzyme is
met-tyrosinase [Cu(II)2] and activation, associated with a 'lag period', involves
reduction to deoxy-tyrosinase [Cu(I)2] which is capable of binding dioxygen to form
oxy-tyrosinase [Cu(II)2·O2]. Initially the conversion of met- to deoxy-tyrosinase
is brought about by a catechol that is indirectly formed from an ortho-quinone product
of tyrosinase action. The primary function of the enzyme is monooxygenation of phenols
to ortho-quinones by oxy-tyrosinase. Inactivation of the enzyme results from monooxygenase
processing of catechols which can lead to reductive elimination of one of the active-site
copper ions and conversion of oxy-tyrosinase to the inactive deact-tyrosinase [Cu(II)Cu(0)].
This review describes the tyrosinase pathways and the role of each oxidation state
in the enzyme's oxidative transformations of phenols and catechols.