Anhui Province Key Laboratory of Farmland Ecological Conservation and Pollution Prevention, School of Resources and Environment, Anhui Agricultural University, 130 Changjiang West Road, Hefei, 230036, Anhui, China.
Anhui Province Key Laboratory of Farmland Ecological Conservation and Pollution Prevention, School of Resources and Environment, Anhui Agricultural University, 130 Changjiang West Road, Hefei, 230036, Anhui, China.
Chemosphere. 2020 Nov;258:127371. doi: 10.1016/j.chemosphere.2020.127371. Epub 2020 Jun 11.
Fungal laccase has aroused great concern in rapidly removing estrogens because of its ability to accelerate humification and oligomerization. Here, the effect of two humic acids (HAs) on the reaction kinetics and products distribution of 17α-ethynylestradiol (EE2) in laccase-initiated humification and coupling was systematically elucidated. Laccase from Trametes versicolor exhibited over 98.3% removal rate for EE2 at pH 5.0 within 120 min, while HAs invariably restrained EE2 transformation by competing with target-substrate for the enzymatic catalytic center. EE2 removal followed pseudo-first-order kinetics, and the rate constant was decreased markedly with increasing concentration of two HAs (0-60 mg L). Additionally, laccase heightened the aromaticity and humification degrees (A/A ratio) of HAs probably due to the formation of new humic polymers such as (HA) and/or (HA)-(EE2) (m and n represent the number of HA and EE2 units, respectively). Three major EE2 oligomers were identified, in accordance with a mechanism involving the phenoxy radical-driven polymerization to yield a wide variety of self-coupling products. Notably, HAs diminished the extent of EE2 self-coupling but aggrandized the cross-coupling between EE2 and HAs, and the inhibition degree of EE2 self-coupling increased with the concentration of HAs. One major reason is EE2 could be covalently incorporated into humic molecules to produce (HA)-(EE2) cross-coupling products via radical-caused C-C, C-O-C, and/or C-O-C bonds, thereby reducing EE2 self-oligomerization. These findings highlight that HAs play a vital role in the fungal laccase-induced humification and oligomerization of EE2, which obviously alter the geochemical fate and transport of EE2 in natural aquatic ecosystems.
真菌漆酶因其能够加速腐殖化和低聚物化而引起了人们对快速去除雌激素的极大关注。在这里，系统地研究了两种腐殖酸（HA）对漆酶引发的腐殖化和偶联过程中 17α-乙炔基雌二醇（EE2）反应动力学和产物分布的影响。在 pH 值为 5.0 时，来自变色栓菌的漆酶在 120 分钟内对 EE2 的去除率超过 98.3%，而 HA 总是通过与目标底物竞争酶催化中心来抑制 EE2 的转化。EE2 的去除遵循准一级动力学，随着两种 HA（0-60 mg/L）浓度的增加，速率常数显著降低。此外，漆酶可能会提高 HA 的芳香度和腐殖化程度（A/A 比），这可能是由于形成了新的腐殖聚合物，如（HA）和/或（HA）-（EE2）（m 和 n 分别代表 HA 和 EE2 单元的数量）。根据涉及酚氧基自由基引发聚合生成各种自偶联产物的机制，鉴定出三种主要的 EE2 低聚物。值得注意的是，HA 降低了 EE2 自偶联的程度，但增大了 EE2 和 HA 之间的交叉偶联，并且 EE2 自偶联的抑制程度随着 HA 浓度的增加而增加。一个主要原因是 EE2 可以通过自由基引起的 C-C、C-O-C 和/或 C-O-C 键共价结合到腐殖质分子中，生成（HA）-（EE2）交叉偶联产物，从而减少 EE2 自低聚物化。这些发现强调了 HA 在真菌漆酶诱导 EE2 腐殖化和低聚化中的重要作用，这明显改变了 EE2 在自然水生态系统中的地球化学归趋和迁移。
