title: Effect of ionic liquids alkyl chain length on horseradish peroxidase thermal inactivation kinetics and activity recovery after inactivation.
abstract: The effects of different alkyl chain lengths of ionic liquids 1-ethyl-, 1-butyl- and 1-hexyl-3-methylimidazolium chloride, on the catalytic activity, thermal stability and deactivation kinetics of horseradish peroxidase were studied in the temperature range of 45-85 °C. The presence of 1-ethyl- and 1-butyl-ionic liquids up to 25% (w/v) did not affect significantly the enzyme activity at 25 °C, whereas the addition of 1-hexyl-solvent resulted in lower activity of enzyme. Typical biphasic deactivation profiles were obtained and adequately fitted by a bi-exponential equation. When increasing ionic liquids concentration up to 25% (w/v), the second phase of deactivation became more prominent, till leading to apparent first-order kinetics. Occurrence of activity regain, following thermal deactivation was found, reaching up 60-80% of the initial activity, especially in 1-hexyl-3-methylimidazolium chloride. Activity regain was particularly noticeable in the first phase of deactivation. Temperature sensitivity of the Soret band maxima indicated that the enzyme prepared in buffer or 1-hexyl-3-methylimidazolium chloride had similar conformational changes in the haem region, but no correlations were found with activity decrease.
authors.affiliation: QOPNA, Department of Chemistry, University of Aveiro, 3810-193, Aveiro, Portugal, fmachado@ua.pt.
authors.forename: Maria F
authors.initials: MF
authors.lastname: Machado
authors.forename: Rui P
authors.initials: RP
authors.lastname: Queirós
authors.forename: Mauro D
authors.initials: MD
authors.lastname: Santos
authors.forename: Liliana G
authors.initials: LG
authors.lastname: Fidalgo
authors.forename: Ivonne
authors.initials: I
authors.lastname: Delgadillo
authors.forename: Jorge A
authors.initials: JA
authors.lastname: Saraiva
mesh_terms: D004791:Enzyme Inhibitors / Q000378:metabolism*; D006735:Horseradish Peroxidase / Q000378:metabolism*; D007093:Imidazoles / Q000378:metabolism*; D052578:Ionic Liquids / Q000378:metabolism*; D013696:Temperature
chemical_list: D004791:Enzyme Inhibitors; D007093:Imidazoles; D052578:Ionic Liquids; D006735:Horseradish Peroxidase