Naish-Byfield S, Riley P A
Department of Biology and Biochemistry, Brunel University, Uxbridge, United Kingdom.
Pigment Cell Res. 1998 Jun;11(3):127-33. doi: 10.1111/j.1600-0749.1998.tb00722.x.
Evidence is presented for the binding of the quinone oxidation product of the monohydric phenol substrate, 4-hydroxyanisole, to mushroom tyrosinase. Column chromatography and SDS-PAGE separation showed labelling of the enzyme when incubated with 14C ring-labelled 4-hydroxyanisole. It is proposed that covalent binding to the enzyme and other proteins is through reaction of accessible nucleophilic groups, including thiols and amino groups, with the anisylquinone. This reductive addition enables the indirect generation of the catecholic substrate, which acts as an electron donor for the bicupric active site of met-tyrosinase and explains the lag kinetics of tyrosinase oxidation of non-cyclizing substrates. The effects of diluting the enzyme or the addition of amino acids on the lag period was consistent with a mechanism involving indirect generation of the dihydric phenol, which acts as the met-enzyme-recruiting substrate.
有证据表明一元酚底物4-羟基苯甲醚的醌氧化产物与蘑菇酪氨酸酶结合。柱色谱和SDS-PAGE分离显示，当与14C环标记的4-羟基苯甲醚一起孵育时，该酶会被标记。有人提出，与该酶和其他蛋白质的共价结合是通过可及的亲核基团（包括硫醇和氨基）与茴香基醌的反应实现的。这种还原加成使得儿茶酚底物能够间接生成，该底物作为变构酪氨酸酶双铜活性位点的电子供体，并解释了非环化底物酪氨酸酶氧化的滞后动力学。稀释酶或添加氨基酸对滞后时间的影响与涉及间接生成二元酚的机制一致，该二元酚作为变构酶招募底物。
