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Versatile peroxidase degradation of humic substances: Use of isothermal titration calorimetry to assess kinetics, and applications to industrial wastes

Paper ID Volume ID Publish Year Pages File Format Full-Text
23233 43422 2014 11 PDF Available
Title
Versatile peroxidase degradation of humic substances: Use of isothermal titration calorimetry to assess kinetics, and applications to industrial wastes
Abstract

•ITC was used for the first time to study kinetics of humic substances degradation.•The kinetics of versatile-peroxidase oxidation of humic substances was sigmoidal.•The peroxidase reactions exhibited product inhibition or synergistic activation.•The enzyme's allosteric behaviour promotes a high level of regulation of activity.•Degradation products were examined by electrospray ionization mass spectrometry.

The kinetic constants of a hybrid versatile-peroxidase (VP) which oxidizes complex polymeric humic substances (HS) derived from lignin (humic and fulvic acids) and industrial wastes were determined for the first time using isothermal titration calorimetry (iTC). The reaction conditions were manipulated to enable manganese-peroxidase (MnP) and/or lignin-peroxidase (LiP) activities to be evaluated. The peroxidase reactions exhibited varying degrees of product inhibition or activation; properties which have not previously been reported for VP enzymes. In contrast to previous work (Ertan et al., 2012) on small non-polymeric substrates (MnSO4, veratryl alcohol and dyes), all kinetic plots for polymeric HS were sigmoidal, lacked Michaelis–Menten characteristics, and were indicative of positive cooperativity. Under conditions when both LiP and MnP were active, the kinetic data fitted to a novel biphasic Hill Equation, and the rate of enzymatic reaction was significantly greater than the sum of individual LiP plus MnP activities implying synergistic activation. By employing size-exclusion chromatography and electrospray ionization mass spectrometry, the characteristics of the oxidative degradation products of the HS were also monitored. Our study showed that the allosteric behaviour of the VP enzyme promotes a high level of regulation of activity during the breakdown of model and industrial ligninolytic substrates. The work was extended to examine the kinetics of breakdown of industrial wastes (effluent from a pulp and paper plant, and fouled membrane solids extracted from a ground water treatment membrane) revealing unique, VP-mediated, kinetic responses. This work demonstrates that iTC can be successfully employed to study the kinetic properties of VP enzymes in order to devise reaction conditions optimized for oxidative degradation of HS present in materials used in a wide range of industries.

Keywords
HS, humic substances; FA, fulvic acid; HA, humic acid; PPE, paper and pulp effluent; FMS, fouled membrane solids; VP, versatile-peroxidase; VP-BA, VP from Bjerkendera adusta; LiP, lignin-peroxidase; MnP, manganese-peroxidase; LiP-MnP, combined LiP and MnP
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Versatile peroxidase degradation of humic substances: Use of isothermal titration calorimetry to assess kinetics, and applications to industrial wastes
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Biotechnology - Volume 178, 20 May 2014, Pages 1–11
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us