Garcia-Jimenez Antonio, Teruel-Puche Jose Antonio, Garcia-Ruiz Pedro Antonio, Saura-Sanmartin Adrian, Berna Jose, Garcia-Canovas Francisco, Rodriguez-Lopez José Neptuno
GENZ-Group of Research on Enzymology, Department of Biochemistry and Molecular Biology-A, Regional Campus of International Excellence "Campus Mare Nostrum", University of Murcia, Espinardo, Murcia, Spain.
Group of Molecular Interactions in Membranes, Department of Biochemistry and Molecular Biology-A, University of Murcia, Espinardo, Murcia, Spain.
PLoS One. 2017 Nov 14;12(11):e0187845. doi: 10.1371/journal.pone.0187845. eCollection 2017.
Deoxyarbutin, a potent inhibitor of tyrosinase, could act as substrate of the enzyme. Oxytyrosinase is able to hydroxylate deoxyarbutin and finishes the catalytic cycle by oxidizing the formed o-diphenol to quinone, while the enzyme becomes deoxytyrosinase, which evolves to oxytyrosinase in the presence of oxygen. This compound is the only one described that does not release o-diphenol after the hydroxylation step. Oxytyrosinase hydroxylates the deoxyarbutin in ortho position of the phenolic hydroxyl group by means of an aromatic electrophilic substitution. As the oxygen orbitals and the copper atoms are not coplanar, but in axial/equatorial position, the concerted oxidation/reduction cannot occur and the release of a copper atom to bind again in coplanar position, enabling the oxidation/reduction or release of the o-diphenol from the active site to the medium. In the case of deoxyarbutin, the o-diphenol formed is repulsed by the water due to its hydrophobicity, and so can bind correctly and be oxidized to a quinone before being released. Deoxyarbutin has been characterized with: [Formula: see text] = 1.95 ± 0.06 s-1 and [Formula: see text] = 33 ± 4 μM. Computational simulations of the interaction of β-arbutin, deoxyarbutin and their o-diphenol products with tyrosinase show how these ligands bind at the copper centre of tyrosinase. The presence of an energy barrier in the release of the o-diphenol product of deoxyarbutin, which is not present in the case of β-arbutin, together with the differences in polarity and, consequently differences in their interaction with water help understand the differences in the kinetic behaviour of both compounds. Therefore, it is proposed that the release of the o-diphenol product of deoxyarbutin from the active site might be slower than in the case of β-arbutin, contributing to its oxidation to a quinone before being released from the protein into the water phase.
脱氧熊果苷是一种有效的酪氨酸酶抑制剂，它可以作为该酶的底物。氧化型酪氨酸酶能够使脱氧熊果苷羟基化，并通过将生成的邻二酚氧化为醌来完成催化循环，同时该酶转变为脱氧型酪氨酸酶，后者在有氧存在的情况下又会演变为氧化型酪氨酸酶。这种化合物是目前所描述的唯一一种在羟基化步骤后不会释放邻二酚的物质。氧化型酪氨酸酶通过芳香亲电取代作用使脱氧熊果苷在酚羟基的邻位发生羟基化。由于氧轨道和铜原子并非共面，而是处于轴向/赤道位置，所以无法发生协同氧化/还原反应，也不会释放出一个铜原子以便在共面位置重新结合，从而实现氧化/还原反应或使邻二酚从活性位点释放到介质中。就脱氧熊果苷而言，所形成的邻二酚因其疏水性而被水排斥，因此能够正确结合并在释放之前被氧化为醌。脱氧熊果苷的特征在于：[公式：见原文] = 1.95 ± 0.06 s-1以及[公式：见原文] = 33 ± 4 μM。β-熊果苷、脱氧熊果苷及其邻二酚产物与酪氨酸酶相互作用的计算模拟表明了这些配体是如何结合在酪氨酸酶的铜中心的。脱氧熊果苷的邻二酚产物释放过程中存在能量屏障，而β-熊果苷的情况并非如此，再加上极性差异以及它们与水相互作用的差异，有助于理解这两种化合物动力学行为的差异。因此，有人提出脱氧熊果苷的邻二酚产物从活性位点的释放可能比β-熊果苷的情况更慢，这使得它在从蛋白质释放到水相之前就被氧化为醌。
