Ramsden Christopher A, Riley Patrick A
Lennard-Jones Laboratories, School of Physical and Geographical Sciences, Keele University, Staffordshire ST5 5BG, UK.
Totteridge Institute for Advanced Studies, The Grange, Grange Avenue, London N20 8AB, UK.
Bioorg Med Chem. 2014 Apr 15;22(8):2388-95. doi: 10.1016/j.bmc.2014.02.048. Epub 2014 Mar 4.
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.
酪氨酸酶是一种广泛分布于生物圈中的酶。它是一组具有高度保守的双铜活性中心、能够结合分子氧的蛋白质之一。酪氨酸酶具有两种催化特性：单加氧酶和氧化酶活性。这些作用反映了活性中心的氧化态。酪氨酸酶有四种可能的氧化态，其相互作用的细节显示出该酶具有异常的动力学行为。该酶的静止状态是高铁酪氨酸酶[Cu(II)2]，而与“延迟期”相关的激活过程涉及还原为脱氧酪氨酸酶[Cu(I)2]，后者能够结合双氧形成氧合酪氨酸酶[Cu(II)2·O2]。最初，高铁酪氨酸酶向脱氧酪氨酸酶的转化是由一种儿茶酚引发的，该儿茶酚是由酪氨酸酶作用产生的邻醌产物间接形成的。该酶的主要功能是通过氧合酪氨酸酶将酚类单加氧化为邻醌。该酶的失活是由于儿茶酚的单加氧酶作用，这可能导致活性位点的一个铜离子发生还原消除，并使氧合酪氨酸酶转化为无活性的失活酪氨酸酶[Cu(II)Cu(0)]。本综述描述了酪氨酸酶的作用途径以及每种氧化态在该酶对酚类和儿茶酚的氧化转化中的作用。
