Catechol 1,2-dioxygenase from Pseudomonas putida was isolated and immobilized in calcium alginate hydrogels. The gel matrix could effectively entrap the enzyme, with high retention of activity. Following immobilization, catechol 1,2-dioxygenase exhibited improved storage stability and activity in the presence of organic solvents, and performed better at higher incubation temperatures. In addition, the enzyme retained most of its catalytic efficiency after successive operational cycles. The hypothesis that enhancement of enzyme stability after immobilization is related to the stabilization of its multimeric structure has been investigated. Electron paramagnetic resonance (EPR) spectroscopy indicates that the environment of the non-heme iron center was not affected during the immobilization process and the ability for the substrate (catechol) binding at the metal center was retained. Catalytic constants for free and immobilized enzyme were practically equivalent. The influence of internal and external mass-transfer limitations on the initial reaction rates of dioxygenase-catalyzed oxidation reactions has been investigated. (c) 2006 Elsevier Inc. All rights reserved.