Conformation, activity and proteolytic stability of acid phosphatase on clay minerals and soil colloids from an Alfisol

doi:10.1016/j.colsurfb.2009.07.031

Colloids and Surfaces B: Biointerfaces

Volume 74, Issue 1, 1 November 2009, Pages 279-283

https://doi.org/10.1016/j.colsurfb.2009.07.031 Get rights and content

Abstract

The present study was carried out to investigate the conformation, enzymatic activity and proteolytic stability of acid phosphatase on montmorillonite, kaolinite and soil colloids from an Alfisol by means of circular dichroism (CD) spectroscopy, isothermal titration microcalorimetry (ITC) and biochemical assay, respectively. The results showed that the secondary structure of phosphatase was changed from disordered type to ordered form during adsorption/desorption cycle, organic substance and 2:1-clay mineral in Brown Soil benefited the formation of ordered structure. Enzymatic activity of phosphatase was inhibited while the proteolytic stability was promoted after the interaction with active particles from permanent charge soil. The decrease of enzymatic activity and the increase of proteolytic stability resulted by montmorillonite and organic colloid were both greater than that by kaolinite and inorganic colloid, which was in consistent with the extent of structural change induced by different colloid particles. Thus, one of the most significant factors responsible for the variation of enzymatic activity and proteolytic stability might be the hiding or even damage of active sites and the irrecognition of cleavage sites in enzyme molecules induced by the formation of ordered structure. The information obtained in this study is of crucial significance for the understanding of the behavior and fate of extracellular enzymes in soils with permanent charges.

Introduction

Soil enzymes play critical roles in maintaining soil productivity and improving soil quality. The activities of soil enzymes have been used as indices of soil fertility, soil quality or soil pollution [1]. The extracellular biomolecules excreted from plant roots and soil microorganisms or faunas are tend to be physically or chemically immobilized on the surface of various soil active particles [2]. The activity and stability of enzymes might be promoted, inhibited or maintained after immobilization [3], [4], [5], [6], [7], [8], [9].

The structure of enzymes adsorbed on soil colloidal particles has been investigated by a number of studies. FTIR spectroscopy analysis revealed that the adsorption of ovPrP on montmorillonite induced an increase in β-structures and a loss in α-helices at pHs higher than 4.0 [10]. However, reduced amounts of β-sheet structures were observed for the adsorption of α-chymotrypsin on montmorillonite as the result of water diffusion inside the protein [11].

Structural variations in enzyme molecules interacted with various organic or inorganic soil components or complexes may result in changes in their enzymatic activity and hydrolytic stability by proteinase [12], [13], [14]. The activity and stability of enzymes affected by the interaction with natural soil components or clay minerals have been extensively examined. However, few studies paid attention to the conformational changes of enzymes induced by the interaction with soil colloidal particles and the subsequent consequences in activity and stability of enzymes. Acid phosphatase plays an important role in phosphorus cycles of soils. The aim of the present study was to investigate the conformation, enzymatic activity and proteolytic stability of acid phosphatase influenced by its interaction with the active colloidal particles separated from an Alfisol which is a typical permanent charge soil by means of circular dichroism (CD) spectroscopy, isothermal titration microcalorimetry (ITC) and biochemical assay, respectively.

Section snippets

Enzyme

Acid phosphatase (EC3.1.3.2 Type II, 1.0 units mg⁻¹ from potato) was purchased from Sigma Chemical Co., St. Louis, MO.

Soil colloids and minerals

Brown soil (Alfisol, pH 7.0) was sampled at the depth of 0–17 cm from Taishan, Shandong province, China. After removal of organic residue, the soil was rinsed in deionized water and the pH value of suspension was adjusted to 7–8 by the addition of 0.01 mol L⁻¹ NaOH or HCl solution. The suspension was dispersed by sonication for 30 min and the <2 μm colloidal fraction was separated by

Conformational change of acid phosphatase

The CD spectra of phosphatase before adsorption (native state) and after adsorption (desorbed state) are shown in Fig. 1. The investigation of phosphatase in adsorbed state was restrained by the light scattering caused by dark color of soil colloids and minerals. The spectral profile of phosphatase in native state showed a negative band with a minimum ellipticity at 221 nm. The single extreme valley of desorbed phosphatase from montmorillonite and kaolinite were both shifted to 217 nm while that

Discussions

Two opposite trends for the transformation of secondary structure of protein molecules induced by the interaction with solid surfaces have been reported previously. The one is from ordered type to disordered form, such as the adsorption of BSA on hydrophilic silica particles [17]. The other is from irregular type to regular form like the adsorption of α-chymotrypsin on hydrophobic Teflon surface [18]. Hydrophobic interactions have been considered as the critical force responsible for the

Acknowledgements

The research was financially supported by the National Natural Science Foundation of China (40825002) and the International Foundation for Science (C/2527-2).

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Conformation, activity and proteolytic stability of acid phosphatase on clay minerals and soil colloids from an Alfisol

Abstract

Introduction

Section snippets

Enzyme

Soil colloids and minerals

Conformational change of acid phosphatase

Discussions

Acknowledgements

Enzyme Microb. Technol.

Soil Biol. Biochem.

Soil Biol. Biochem.

Colloid Surf. B

Soil Biol. Biochem.

BBA-Gen. Subj.

J. Colloid Interface Sci.

J. Colloid Interface Sci.

J. Biotechnol.

Biophys. Chem.

J. Colloid Interface Sci.

J. Colloid Interface Sci.

J. Colloid Interface Sci.