title: Versatile peroxidase degradation of humic substances: use of isothermal titration calorimetry to assess kinetics, and applications to industrial wastes.
abstract: 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.
authors.affiliation: School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW 2052, Australia. Electronic address: sohailsiddiqui1995@yahoo.com.
authors.forename: Khawar Sohail
authors.initials: KS
authors.lastname: Siddiqui
authors.affiliation: School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW 2052, Australia; Department of Molecular Biology and Genetics, Istanbul University, Turkey.
authors.forename: Haluk
authors.initials: H
authors.lastname: Ertan
authors.affiliation: School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW 2052, Australia.
authors.forename: Timothy
authors.initials: T
authors.lastname: Charlton
authors.affiliation: Bioanalytical Mass Spectrometry Facility, The University of New South Wales, Sydney, NSW 2052, Australia; School of Medical Sciences, The University of New South Wales, Sydney, NSW 2052, Australia.
authors.forename: Anne
authors.initials: A
authors.lastname: Poljak
authors.affiliation: School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW 2052, Australia.
authors.forename: A K
authors.initials: AK
authors.lastname: Daud Khaled
authors.affiliation: School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW 2052, Australia; College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, North Renmin Road 2999, Shanghai 201620, PR China.
authors.forename: Xuexia
authors.initials: X
authors.lastname: Yang
authors.affiliation: School of Chemical and Biomolecular Engineering, University of Sydney, Sydney, NSW 2006, Australia.
authors.forename: Gavin
authors.initials: G
authors.lastname: Marshall
authors.affiliation: School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW 2052, Australia. Electronic address: r.cavicchioli@unsw.edu.au.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Cavicchioli
mesh_terms: D000494:Allosteric Regulation; D001673:Biodegradation, Environmental; D001709:Biotechnology; D002151:Calorimetry / Q000379:methods*; D055453:Coriolaceae / Q000201:enzymology; D006812:Humic Substances / Q000032:analysis*; D007220:Industrial Waste / Q000032:analysis*; D007700:Kinetics; D008031:Lignin; D008345:Manganese; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000737:chemistry / Q000378:metabolism*
chemical_list: D006812:Humic Substances; D007220:Industrial Waste; D008345:Manganese; D008031:Lignin; D009195:Peroxidase
keywords: Allosteric regulation; Biphasic sigmoidal Hill's plot; Environmental biotechnology; Enzyme kinetics; Lignin-manganese-peroxidase