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Abstract: In this paper we report on the microencapsulation of glucose oxidase from Aspergillus niger (GOx) and laccase from Trametes versicolor (TvL) with the goal of immobilizing these enzymes in paper substrates to develop biosensors and bioreactors. Despite having high encapsulation efficiency, the technique caused a severe decrease (up to 65%) in the specific activities of both enzymes once microencapsulated. Encapsulated TvL presented lower K M and V max values compared to free laccase in solution, but the K M for GOx did not change after microencapsulation. TvL was found to interact strongly with poly(ethyleneimine) (PEI) in a manner similar to that expected from an uncompetitive inhibition mechanism, and fluorescence and circular dichroism spectroscopy demonstrated that significant alteration of the enzyme''s conformation occurs in the presence of PEI, an effect of the cationic polymer that was not observed with GOx. Microencapsulation improved the thermal stability of GOx at temperatures up to 60°C due to stabilization of its active conformation but reduced the thermal stability of laccase because of the increased coordination between PEI and copper atoms in the enzyme''s active site. Preliminary GOx bioactive paper was fabricated, which could be potentially used as food packaging paper. [Copyright &y& Elsevier]