P-MDB, a pH-sensitive and reversible water-soluble copolymer, was synthesized with methacrylic acid (MM), 2-(dimethylamino) ethyl methacrylate (DMAEMA), and butyl methacrylate (BMA) and used as carrier for cellulase. The copolymer is insoluble between pH 2.5 and 4.1, and soluble below pH 2.5 or above 4.1. Its recovery in aqueous solution was 97.2% by adjusting its isoelectric point (pI) to 3.1. Cellulase was covalently immobilized on P-MDB with 1-ethyl-3-(3-dimethyllaminopropyl) carbodiimide. Under optimized conditions, the activity yield of immobilized cellulase was 63.24% and its recovery was 96.8% by adjusting the pl to 3.5. Maximum activity of the immobilized cellulase was achieved at 60 degrees C (pH 5.0), while free cellulase exhibited maximum activity at 55 degrees C (pH 5.0). The immobilized cellulase retained 83.1% of its initial activity after repeated five cycles of hydrolysis reaction. P-MDB is a promising carrier for immobilizing enzymes with high and low optimum pH due to its dissolving characteristics. (C) 2012 Elsevier Ltd. All rights reserved.