BACKGROUNDStudies with peroxidase (EC 1.11.1.7) have demonstrated that phenolic precipitate adsorbs free enzyme, inactivating it. The end-product inactivation model has been proposed to explain the effect. Additives, such as polyethylene glycol and Triton X-100, were reported to effectively extend enzyme lifetime by preventing the adsorption. RESULTSIt was found that soybean peroxidase (SBP, EC 1.11.1.7) trapped in precipitate during phenol polymerization retains activity. Contrary to the end-product inactivation model, recycling precipitate effectively utilized the active SBP. The minimum SBP concentration required for the subsequent batch reaction removal of 1mmolL(-1) phenol from aqueous solution was reduced from 1.2 to 0.5 U mL(-1). SBP adsorption on the precipitate was proven to be reversible by the addition of Triton X-100. Thus, a new explanation of SBP fate during the reaction is suggested: SBP is immobilized in situ in an active form with reduction of specific activity rather than inactivation. The adsorption is characterized by a Langmuir isotherm. CONCLUSIONSThe phenolic precipitate immobilizes SBP in an active form, consistent with the Langmuir isotherm model. Recycling the precipitate improves the enzyme economy in phenol removal. (c) 2013 Society of Chemical Industry