PEGylated horseradish peroxidase (PEG-HRP) was prepared by reacting activated monomethoxy poly(ethylene glycol) with horseradish peroxidase (HRP). Quantitative conversion of HRP to PEG-HRP was observed at a HRP to PEG molar ratio of 1-250 in pH 9.0 borate buffer at 25 degrees C for 3 h. The PEG-HRP conjugates obtained are soluble in various hydrophobic solvents including toluene and benzene. The PEG-HRP conjugates exhibit higher activity than the native HRP with and without the inclusion of equivalent amount of free PEG. Upon conjugation the optimal reaction temperature was increased by 30 degrees C. The PEG-HRP conjugates are relatively active in acetonitrile and dimethylformamide and are capable of catalysing the polymerization of 2-naphthol for the production of fluorescent poly(2-naphthol). The average molecular weight of the polymers, ranging from 900 to 1700, is affected by the concentration of acetonitrile in the reaction medium and is higher than that obtained with the reversed micellar system. The ease of separation of the synthesized polymers from the PEG-HRP conjugates can facilitate the recycling of enzymes. (c) 2006 Elsevier Ltd. All rights reserved.