title: Laccase immobilization over multi-walled carbon nanotubes: Kinetic, thermodynamic and stability studies.
abstract: The biocatalytic performance of immobilized enzyme systems depends mostly on the intrinsic properties of both biomolecule and support, immobilization technique and immobilization conditions. Multi-walled carbon nanotubes (MWCNTs) possess unique features for enzyme immobilization by adsorption. Enhanced catalytic activity and stability can be achieved by optimization of the immobilization conditions and by investigating the effect of operational parameters. Laccase was immobilized over MWCNTs by adsorption. The hybrid material was characterized by Fourier transformed infrared (FTIR) spectroscopy, scanning and transmission electron microscopy (SEM and TEM, respectively). The effect of different operational conditions (contact time, enzyme concentration and pH) on laccase immobilization was investigated. Optimized conditions were used for thermal stability, kinetic, and storage and operational stability studies. The optimal immobilization conditions for a laccase concentration of 3.75μL/mL were a pH of 9.0 and a contact time of 30min (522 Ulac/gcarrier). A decrease in the thermal stability of laccase was observed after immobilization. Changes in ΔS and ΔH of deactivation were found for the immobilized enzyme. The Michaelis-Menten kinetic constant was higher for laccase/MWCNT system than for free laccase. Immobilized laccase maintained (or even increased) its catalytic performance up to nine cycles of utilization and revealed long-term storage stability.
authors.affiliation: LCM - Laboratory of Catalysis and Materials, LSRE - Laboratory of Separation and Reaction Engineering, Associate Laboratory LSRE-LCM, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal. Electronic address: aptavares@ua.pt.
authors.forename: Ana P M
authors.initials: AP
authors.lastname: Tavares
authors.affiliation: LCM - Laboratory of Catalysis and Materials, LSRE - Laboratory of Separation and Reaction Engineering, Associate Laboratory LSRE-LCM, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal.
authors.forename: Cláudia G
authors.initials: CG
authors.lastname: Silva
authors.affiliation: Department of Nanostructured Materials, Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia; Laboratory for Materials Chemistry, National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia.
authors.forename: Goran
authors.initials: G
authors.lastname: Dražić
authors.affiliation: LCM - Laboratory of Catalysis and Materials, LSRE - Laboratory of Separation and Reaction Engineering, Associate Laboratory LSRE-LCM, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal.
authors.forename: Adrián M T
authors.initials: AM
authors.lastname: Silva
authors.affiliation: LCM - Laboratory of Catalysis and Materials, LSRE - Laboratory of Separation and Reaction Engineering, Associate Laboratory LSRE-LCM, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal.
authors.forename: José M
authors.initials: JM
authors.lastname: Loureiro
authors.affiliation: LCM - Laboratory of Catalysis and Materials, LSRE - Laboratory of Separation and Reaction Engineering, Associate Laboratory LSRE-LCM, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal.
authors.forename: Joaquim L
authors.initials: JL
authors.lastname: Faria
mesh_terms: D000327:Adsorption; D001236:Aspergillus oryzae / Q000737:chemistry / Q000201:enzymology; D004795:Enzyme Stability; D004800:Enzymes, Immobilized / Q000737:chemistry* / Q000302:isolation & purification; D017743:Equipment Reuse; D005656:Fungal Proteins / Q000737:chemistry* / Q000302:isolation & purification; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D042845:Laccase / Q000737:chemistry* / Q000302:isolation & purification; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000648:ultrastructure; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D013816:Thermodynamics
chemical_list: D004800:Enzymes, Immobilized; D005656:Fungal Proteins; D037742:Nanotubes, Carbon; D042845:Laccase
keywords: Characterization; Kinetics; Laccase immobilization; Multi-walled carbon nanotubes; Thermodynamics