Ether Hydrolysis, Ether Thiolysis, and the Catalytic Power of Etherases in the Disassembly of Lignin.,Biochemistry

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Ether Hydrolysis, Ether Thiolysis, and the Catalytic Power of Etherases in the Disassembly of Lignin.
Biochemistry ( IF 2.9 ) Pub Date : 2019-11-11 , DOI: 10.1021/acs.biochem.9b00698
Charles A Lewis ₁ , Richard Wolfenden ₁

Affiliation

The recycling of much of the carbon in Nature depends on the breakdown of polymers in woody matter, notably cellulose (a polyacetal) and lignin (a polyether). Here, we show that equilibrium favors ether hydrolysis in water, although the rates of spontaneous hydrolysis of ethers are too slow to measure in neutral solution except at temperatures approaching the critical point of water. Circumventing that kinetic obstacle, glutathione-dependent etherases from white-rot fungi are known to employ the thiolate group of glutathione to attack guaiacyl ethers. Experiments at elevated temperatures indicate that thioglycolate attacks diethyl ether in water, in the absence of enzymes, with a rate constant of 6 × 10-11 M-1 s-1 at 25 °C and that ether thiolysis is strongly favored thermodynamically, with a Keq value of 2.5 × 106 (ΔG = -8.7 kcal/mol). Compared with the rate of non-enzymatic thiolysis, the lignin-degrading etherases LigE and LigF produce 1015-fold rate enhancements, among the largest that have been observed for an enzyme acting on two substrates.

中文翻译：

木质素分解中的醚水解，醚硫解和醚酶的催化能力。

自然界中大部分碳的循环利用取决于木质物质中聚合物的分解，特别是纤维素（聚缩醛）和木质素（聚醚）的分解。在这里，我们表明平衡有利于水中的醚水解，尽管醚的自发水解速度太慢，无法在中性溶液中测量，除非温度接近水的临界点。绕过动力学障碍，白腐真菌的谷胱甘肽依赖性醚酶已知利用谷胱甘肽的硫醇盐基团攻击愈创木醚。在升高的温度下进行的实验表明，巯基乙酸盐在不存在酶的情况下以25×C的速率常数为6×10-11 M-1 s-1的速率攻击水中的乙醚，并且热力学上强烈支持醚硫解， Keq值为2.5×106（ΔG= -8.7 kcal / mol）。

更新日期：2019-11-11

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