Clay Minerals Change the Toxic Effect of Cadmium on the Activities of Leucine Aminopeptidase

Shunyu Huang,Jipeng Wang,Jingji Li,Qiaohui Fan

doi:10.1155/2021/1024085

Shunyu Huang, Jipeng Wang + Show 2 more

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https://doi.org/10.1155/2021/1024085

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Abstract

Soil leucine aminopeptidase (LAP) is a hydrolytic enzyme involved in the acquisition of nitrogen by microorganisms. In contaminated soils, LAP activity is affected not only by the type and concentration of heavy metals but also by the form of enzyme. Here, we investigated the degree and mechanism of cadmium (Cd) inhibition of soil LAP and purified LAP. We also examined the effect of montmorillonite and kaolinite on LAP and LAP contaminated with Cd. The results showed that Cd inhibition of LAP activity increased with increasing Cd concentration and that Cd exerted noncompetitive inhibition of LAP. The addition of clay minerals decreases LAP activity and the maximum reaction rate ([Formula: see text]), regardless of the presence of Cd. Montmorillonite decreases the affinity of LAP to the substrate ([Formula: see text]), while kaolinite increases the affinity of LAP to the substrate. The clay mineral-immobilized LAP showed an increase in resistance to Cd contamination compared with the free LAP. The results obtained in this study may aid in understanding the toxic effects of heavy metals on soil enzymes.

Highlights

Cadmium (Cd) has become one of the most hazardous heavy metals in soil as a result of its potential, persistent, and irreversible toxicity [1,2,3]
Since soil enzyme activity is closely related to soil microorganisms and is sensitive to changes in environmental conditions, soil enzyme activity is often used as an indicator to evaluate the level to which heavy metals influence soil microbial function and soil ecosystem health [8,9,10,11,12]
Cd inhibited the enzymatic reaction by disrupting the conformation of the enzyme protein, which cannot be restored by adding the metals associated with the leucine aminopeptidase (LAP) active site

Summary

Introduction

Cadmium (Cd) has become one of the most hazardous heavy metals in soil as a result of its potential, persistent, and irreversible toxicity [1,2,3]. When Cd enters soil, it affects the environmental health of the soil and the stability of ecosystem, soil microorganisms [4, 5]. Since soil enzyme activity is closely related to soil microorganisms and is sensitive to changes in environmental conditions, soil enzyme activity is often used as an indicator to evaluate the level to which heavy metals influence soil microbial function and soil ecosystem health [8,9,10,11,12]. The extent of soil enzyme activity in response to heavy metals is related to the type and concentration of heavy metals and to the type of soil enzyme and soil properties, such as clay mineral content [17, 18] The soil enzyme activity exponentially decreases with increasing heavy metal concentrations by displacing enzyme conformation-related metals and occupying the active center of the enzyme or by binding to sulfhydryl, amino, and carboxyl groups in the enzyme structure to reduce the active site of the enzyme [13,14,15,16].

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