PHENOL REMOVAL BY MODIFIED PEROXIDASES

Horseradish peroxidase (HRP) catalyses the oxidation of toxic aromatic compounds, especially phenols, in the presence of hydrogen peroxide. Reaction products polymerise to form insoluble precipitates which read ily separate from aqueous solution, unlike their monomeric precursors. High-temperature phenol-containing gas liquors (produced from coal co nversion processes) or effluent from bleach plants of kraft mills can substantially affect the stability of enzymes such as HRP and thus the ir oxidation capabilities. Apparent inactivation of peroxidase during high temperature polymerisation reactions is mainly due to unfolding o f the protein backbone. The catalytic lifetime of HRP at high temperat ures can be extended by chemical modification of lysine epsilon-amino groups using succinimides. The bifunctional, ethylene glycol bis-succi nimidyl succinate (EG-NHS) and the monofunctional, acetic acid N-hydro xysuccinimide ester (AA-NHS) were used. The extent of stabilisation is dependent on the nature and concentration of the reagent used. The op timum pH for phenol removal is 9.0 (8.0 for 4-chlorophenol) for both n ative and modified forms of the enzyme; the optimum molar ratio of hyd rogen peroxide and phenolic substrate is around 1.0. The effects of pe roxide and enzyme concentration on the polymerisation reaction were in vestigated. HRP derivatives significantly reduced the oxidation reacti on time at 70 degrees C.