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Ionic polymer-coated laccase with high activity and enhanced stability: application in the decolourisation of water containing AO7.

Zhang X, Hua M, Lv L, Pan B - Sci Rep (2015)

Bottom Line: The stability of the resulting LacPG was highly enhanced against pH variations, thermal treatments and provided better long-term storage with a negligible loss in enzymatic activity.Compared to Lac, LacPG exhibited significantly higher decolourisation efficiency in the degradation of a representative azo dye, acid orange 7 (AO7), which resulted from the electrostatic attraction between the coating and AO7.The increased size and modified surface chemistry of LacPG facilitated ultrafiltration and reduced membrane fouling.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, P.R. China.

ABSTRACT
Eliminating dyes in environmental water purification remains a formidable challenge. Laccase is a unique, environmentally friendly and efficient biocatalyst that can degrade pollutants. However, the use of laccase for the degradation of pollutants is considerably limited by its susceptibility to environmental changes and its poor reusability. We fabricated a novel biocatalyst (LacPG) by coating polyethylenimine onto the native laccase (Lac) followed by crosslinking with glutaraldehyde. The stability of the resulting LacPG was highly enhanced against pH variations, thermal treatments and provided better long-term storage with a negligible loss in enzymatic activity. Compared to Lac, LacPG exhibited significantly higher decolourisation efficiency in the degradation of a representative azo dye, acid orange 7 (AO7), which resulted from the electrostatic attraction between the coating and AO7. LacPG was separated from the AO7 solution using an ultrafiltration unit. The increased size and modified surface chemistry of LacPG facilitated ultrafiltration and reduced membrane fouling. LacPG exhibited enhanced stability, high catalytic activity and favourable properties for membrane separation; therefore, LacPG could be continuously reused in an enzymatic membrane reactor with a high efficiency for decolourising water containing AO7. The developed strategy appears to be promising for enhancing the applicability of laccase in practical water treatment.

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Related in: MedlinePlus

(a) Storage stabilities of Lac and LacPG and (b) far-UV CD spectra of Lac and LacPG before and after 60 days of storage (pH 7.0, 40°C); error bars show standard deviations for at least three measurements; all of the presented CD spectra were averaged over at least five scans, and the contribution from the background buffer solution was subtracted.
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f4: (a) Storage stabilities of Lac and LacPG and (b) far-UV CD spectra of Lac and LacPG before and after 60 days of storage (pH 7.0, 40°C); error bars show standard deviations for at least three measurements; all of the presented CD spectra were averaged over at least five scans, and the contribution from the background buffer solution was subtracted.

Mentions: Good storage stability is an essential requirement for a biocatalyst to be used in industrial applications. It is well known that high temperatures are detrimental to the storage of enzymes. Thus, the storage stabilities of Lac and LacPG were examined at 40°C, which could be considered to be scorching weather, and the results are shown in Fig. 4(a). Lac lost ca. 80% and 100% of its activity after 5 days and 60 days of storage, respectively, whereas no loss in activity was detected for LacPG. We explored the secondary conformations of Lac and LacPG by recording their circular dichroism (CD) spectra before and after 60 days of storage (Fig. 4(b)). The crosslinked PEI coatings had little effect on the secondary conformation of Lac, and the CD spectrum of fresh Lac had a similar shape to that of fresh LacPG, in which the negative peak at approximately 231 nm was assigned to the arrangements of β-sheets in the secondary structure41. After 60 days of storage, there was a considerable change in the CD spectrum of Lac, e.g., the negative peak at ≃231 nm shifted to ≃225 nm and increased in intensity, indicating a conformational change in Lac resulting from storage. However, 60 days of storage had a negligible effect on the CD spectrum of LacPG, and only a slight increase in the intensity of the negative peak at ≃231 nm was observed, indicating that the secondary structure of LacPG was stable.


Ionic polymer-coated laccase with high activity and enhanced stability: application in the decolourisation of water containing AO7.

Zhang X, Hua M, Lv L, Pan B - Sci Rep (2015)

(a) Storage stabilities of Lac and LacPG and (b) far-UV CD spectra of Lac and LacPG before and after 60 days of storage (pH 7.0, 40°C); error bars show standard deviations for at least three measurements; all of the presented CD spectra were averaged over at least five scans, and the contribution from the background buffer solution was subtracted.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4317704&req=5

f4: (a) Storage stabilities of Lac and LacPG and (b) far-UV CD spectra of Lac and LacPG before and after 60 days of storage (pH 7.0, 40°C); error bars show standard deviations for at least three measurements; all of the presented CD spectra were averaged over at least five scans, and the contribution from the background buffer solution was subtracted.
Mentions: Good storage stability is an essential requirement for a biocatalyst to be used in industrial applications. It is well known that high temperatures are detrimental to the storage of enzymes. Thus, the storage stabilities of Lac and LacPG were examined at 40°C, which could be considered to be scorching weather, and the results are shown in Fig. 4(a). Lac lost ca. 80% and 100% of its activity after 5 days and 60 days of storage, respectively, whereas no loss in activity was detected for LacPG. We explored the secondary conformations of Lac and LacPG by recording their circular dichroism (CD) spectra before and after 60 days of storage (Fig. 4(b)). The crosslinked PEI coatings had little effect on the secondary conformation of Lac, and the CD spectrum of fresh Lac had a similar shape to that of fresh LacPG, in which the negative peak at approximately 231 nm was assigned to the arrangements of β-sheets in the secondary structure41. After 60 days of storage, there was a considerable change in the CD spectrum of Lac, e.g., the negative peak at ≃231 nm shifted to ≃225 nm and increased in intensity, indicating a conformational change in Lac resulting from storage. However, 60 days of storage had a negligible effect on the CD spectrum of LacPG, and only a slight increase in the intensity of the negative peak at ≃231 nm was observed, indicating that the secondary structure of LacPG was stable.

Bottom Line: The stability of the resulting LacPG was highly enhanced against pH variations, thermal treatments and provided better long-term storage with a negligible loss in enzymatic activity.Compared to Lac, LacPG exhibited significantly higher decolourisation efficiency in the degradation of a representative azo dye, acid orange 7 (AO7), which resulted from the electrostatic attraction between the coating and AO7.The increased size and modified surface chemistry of LacPG facilitated ultrafiltration and reduced membrane fouling.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, P.R. China.

ABSTRACT
Eliminating dyes in environmental water purification remains a formidable challenge. Laccase is a unique, environmentally friendly and efficient biocatalyst that can degrade pollutants. However, the use of laccase for the degradation of pollutants is considerably limited by its susceptibility to environmental changes and its poor reusability. We fabricated a novel biocatalyst (LacPG) by coating polyethylenimine onto the native laccase (Lac) followed by crosslinking with glutaraldehyde. The stability of the resulting LacPG was highly enhanced against pH variations, thermal treatments and provided better long-term storage with a negligible loss in enzymatic activity. Compared to Lac, LacPG exhibited significantly higher decolourisation efficiency in the degradation of a representative azo dye, acid orange 7 (AO7), which resulted from the electrostatic attraction between the coating and AO7. LacPG was separated from the AO7 solution using an ultrafiltration unit. The increased size and modified surface chemistry of LacPG facilitated ultrafiltration and reduced membrane fouling. LacPG exhibited enhanced stability, high catalytic activity and favourable properties for membrane separation; therefore, LacPG could be continuously reused in an enzymatic membrane reactor with a high efficiency for decolourising water containing AO7. The developed strategy appears to be promising for enhancing the applicability of laccase in practical water treatment.

Show MeSH
Related in: MedlinePlus