Agarose coated with polyethyleneimine (PEI) or sulfate-dextran, monoaminoethyl-N-aminoethylagarose, DEAE-agarose and carboxymethyl-agarose was used to immobilize by ionic exchange and alpha-galactosidase from Thermus sp. T2 under different conditions. Supports coated with polymers (PEI or sulfate-dextran) allowed higher immobilization yields (by 10-20%) than mono-functional supports. Moreover, anionic exchangers permitted higher immobilization yields and expressed activities when compared to the cationic exchangers (98% or 67%, respectively under optimal conditions). Curiously, the enzyme could be immobilized on both anionic and cationic exchangers under identical conditions. Both MANAE and PEI-coated supports immobilized the enzyme at pH 7 and gave the highest immobilization yield, expressed activity (over 95%), stability and adsorption strength. Adsorption of the enzyme on PEI-coated supports allowed to greatly increase the enzyme stability at pH 5, 7 and 9 (by over 600-1000 folds), improving the activity at temperatures over the optimal (e.g., at 90 T the free enzyme retained less than 10% of the maximal activity, while the immobilized enzyme retained almost 60%) and at alkaline pH values (e.g., the immobilized enzyme was 4-fold more active at pH 9 than the free enzyme). (C) 2008 Elsevier Ltd. All rights reserved.