腐植酸对漆酶诱导雌激素自聚合动力学的影响

Laccase-induced self-polymerization of estrogens:effect of humic acid on transformation kinetics

本文选择17β-雌二醇(E2)、17α-炔雌醇(EE2)和双酚A(BPA)作为环境中3种典型的代表性雌激素,采用批量平衡试验方法,研究了腐植酸(HA)对变色栓菌(Trametes versicolor)漆酶诱导雌激素转化动力学、产物分布和作用机制的影响。结果表明:漆酶在3 h内对3种雌激素的去除率均高于95%,E2、EE2和BPA的转化动力学常数(k)分别为2.48、2.03 h^(-1)和1.45 h^(-1)。添加HA有效抑制了E2(k=1.04 h^(-1))和EE2(k=0.64 h^(-1))的转化,但促进了BPA的去除(k=3.13 h^(-1)),漆酶诱导HA和长链BPA自聚物发生共聚合反应,所形成的BPA-HA共聚物快速降低了长链BPA自聚物的产量,从而消除了其对漆酶催化活性和稳定性的抑制作用。产物鉴定证实了雌激素的转化产物主要为二聚体、三聚体和四聚体等低聚物。雌激素和HA的共聚合机制分为2个步骤:首先,雌激素和HA被漆酶单电子氧化,该过程形成大量的活性自由基中间体;随后,这些不稳定的活性自由基中间体通过C C、C O C或C N C键共价结合,生成多种结构复杂的雌激素自聚物和共聚物。研究表明,HA能够影响漆酶诱导雌激素自聚合,形成更加复杂的共聚合产物,从而消除环境雌激素污染、封存有机碳。

Laccase is capable of catalyzing the one-electron oxidation of estrogens to produce macromolecular polymers,using dissolved O2 in water as the final electron acceptor.Presently,little information is available regarding the effects of humic acid(HA)on laccaseinduced estrogen self-polymerization.In this study,we selected 17β-estradiol(E2),17α-ethinylestradiol(EE2),and bisphenol A(BPA)as three representative environmental estrogens.The effects of HA on the laccase-induced estrogen transformation kinetics,product distribution,and mechanisms were all systematically investigated.The results of this indicated that the removal efficiencies of the three estrogens by laccase were greater than 95%within 3 h,and that the transformation kinetic constants(k)of E2,EE2,and BPA were 2.48,2.03 h^(-1),and 1.45 h^(-1),respectively.HA effectively inhibited laccase-started E2(k=1.04 h^(-1))and EE2 conversion(k=0.64 h^(-1)),whilst promoting the removal of BPA(k=3.13 h^(-1)).This was likely because laccase-induced HA and BPA co-polymerization rapidly reduced the yields of long-chain BPA self-polymers,thus eliminating their inhibition of catalytic activity and the stability of laccase.Product identification confirmed that the transformation products of the three estrogens were mainly dimers,trimers,tetramers,and oligomers.The co-polymerization mechanisms of estrogen and HA involved two steps here:Firstly,estrogen and HA were oxidized by laccase,which formed many active free radical intermediates.Subsequently,these unstable radical intermediates were covalently bound by C C,C O C,or C N C bonds to generate estrogenic self/co-polymeric products.These findings uncover the co-polymerization mechanisms of estrogen-HA induced by laccase and provide a theoretical basis for eliminating estrogen contamination and sequestrating organic carbon based on enzymatic polymerization.