Meyer Armin H, Penning Holger, Elsner Martin
Institute of Groundwater Ecology, Helmholtz Zentrum Munchen, 85764 Neuherberg, Germany.
Environ Sci Technol. 2009 Nov 1;43(21):8079-85. doi: 10.1021/es9013618.
Transformation of atrazine to hydroxyatrazine in the environment may be underestimated by current assessment schemes since immobilization and further transformation of the metabolite can render parent-to-daughter compound ratios unreliable. This study reports significant C and N isotope fractionation of atrazine in transformation to hydroxyatrazine by Chelatobacter heintzii, Pseudomonas sp. ADP, and Arthrobacter aurescens TC1 highlighting an alternative approach to detecting this natural transformation pathway. Indistinguishable dual isotope slopes big up tri, open (= delta(15)N/delta(13)C approximately epsilon(N)/epsilon(C)) for Chelatobacter heintzii (-0.65 +/- 0.08) and Arthrobacter aurescens TC1 (-0.61 +/- 0.02) suggest the same biochemical transformation mechanism despite different hydrolyzing enzymes (AtzA versus TrzN). With Pseudomonas sp. ADP (also AtzA) significantly smaller fractionation indicates masking effects by steps prior to enzyme catalysis, while a distinguishable big up tri, open = -0.32 +/- 0.06 suggests that some of these steps showed slight isotope fractionation. Abiotic reference experiments reproduced the pattern of biotic transformation at pH 3 (enrichment of (13)C, depletion of (15)N in atrazine), but showed enrichment of both (13)C and (15)N at pH 12. This indicates that the organisms activated atrazine by a similar Lewis acid complexation (e.g., with H(+)) prior to nucleophilic aromatic substitution, giving the first detailed mechanistic insight into this important enzymatic reaction.
由于代谢物的固定化和进一步转化可能使母体与子代化合物的比例变得不可靠，目前的评估方案可能低估了环境中莠去津向羟基莠去津的转化。本研究报告了海因茨螯合杆菌、假单胞菌属ADP和金黄节杆菌TC1在将莠去津转化为羟基莠去津过程中显著的碳和氮同位素分馏，突出了一种检测这种自然转化途径的替代方法。海因茨螯合杆菌（-0.65±0.08）和金黄节杆菌TC1（-0.61±0.02）的双同位素斜率（大三，开式（=δ15N/δ13C≈εN/εC））无法区分，这表明尽管水解酶不同（AtzA与TrzN），但生化转化机制相同。对于假单胞菌属ADP（也是AtzA），显著较小的分馏表明酶催化之前的步骤产生了掩盖效应，而可区分的大三，开式=-0.32±0.06表明其中一些步骤显示出轻微的同位素分馏。非生物对照实验重现了pH 3时生物转化的模式（莠去津中13C富集，15N消耗），但在pH 12时显示13C和15N均富集。这表明生物体在亲核芳香取代之前通过类似的路易斯酸络合（例如与H+）激活莠去津，首次对这一重要的酶促反应给出了详细的机理见解。
