Peroxidase chemically attached on polymeric micelle and its reaction with phenolic compounds

Horseradish peroxidase was chemically modified with comb-shaped polymaleic anhydride-alt-1-tetradecene (PMA-TD) in microemulsion systems to produce surface-active peroxidase that has capability to form micellar structures in aqueous solutions and can be concentrated at liquid/liquid interfaces without unfolding of the enzyme. For chemical modification oil-in-water (O/W) and water-in-oil (W/O) microemulsion systems composed of n-butyl acetate and a buffer solution were prepared because n-butyl acetate turned out to be less detrimental to the activity of peroxidase at high degree of modification compared to other organic solvents. The modification degree of amine groups on the surface of peroxidase by maleic anhydride groups on PMA-TD was reached at equilibrium after 1 h reaction at 0 °C, and 42% of amine groups were modified with 7-fold amount of PMA-TD to peroxidase (wt/wt). The activity of the PMA-TD-modified peroxidase measured with 2,4-dichlorophenol at pH 7.0 was increased by approximately 2-fold compared to native peroxidase. There was no significant shift in optimum pH after modification, and optimum pH measured with 2,4-dichlorophenol was observed at pH 7.0. For all six phenolic compounds tested, there was a significant increase in the reaction efficiency with the PMA-TD-modified peroxidase. The remarkable enhancement of the reaction efficiency by the modification was presumably because of micellar structures of PMA-TD that could concentrate hydrophobic phenolic oligomers into the core of the micelles. Overall, horseradish peroxidase chemically attached to the surface of PMA-TD micelles was found to be significantly effective for the oxidative polymerization of phenolic compounds.