Soil contamination with heavy metal could induce the alteration of soil ecological environments, and soil enzyme activities are sensitive indicators for the soil toxicology. Xylanase is one of predominant soil enzymes related to carbon nitrogen cycle. In this work, we explored the underlying mechanisms for conformational and enzymatic activity alterations of xylanase after silver and lead exposure at molecular level with systematical measurements including multiple spectroscopic methods, isothermal titration calorimetry, and enzymatic activity. Both silver and lead could loosen and unfold the skeleton of xylanase with the quenching of endogenous fluorescence. Silver interacted with xylanase forming larger-size aggregations through Van der Waals forces and hydrogen bonding, while lead interacted with xylanase forming larger-size aggregations through hydrophobic force. Silver and lead induced an obvious loss (67.1 and 56.31%) of the xylanase enzymatic activity, but silver has a greater impact on xylanase than that of lead. The xylanase enzymatic activity significantly decreased due to the conformational alterations. The negative effect of silver exposure on xylanase structure and function was more prominent than that of lead.

中文翻译：

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探索银和铅对木聚糖酶结构和功能的影响：分光光度法和量热法。

重金属污染土壤可能引起土壤生态环境的变化，土壤酶活性是土壤毒理学的敏感指标。木聚糖酶是与碳氮循环有关的主要土壤酶之一。在这项工作中，我们探索了在分子水平上银和铅暴露后木聚糖酶构象和酶活性变化的潜在机制，并进行了系统的测量，包括多种光谱方法，等温滴定量热法和酶活性。随着内源性荧光的猝灭，银和铅都可能使木聚糖酶的骨架松动和展开。银通过范德华力和氢键与木聚糖酶相互作用形成较大的聚集体，而铅与木聚糖酶通过疏水力相互作用形成更大的聚集体。银和铅引起木聚糖酶酶活性的明显损失（67.1％和56.31％），但是银对木聚糖酶的影响比铅更大。由于构象改变，木聚糖酶的酶活性显着降低。银暴露对木聚糖酶结构和功能的负面影响比铅更为突出。