The beta-galactosidase from Thermus sp. T2 (Htag-BgaA) is competitively inhibited by galactose (3.1 mM) and non-competitively inhibited by glucose (49.9 mM). These inhibitions were strongly reduced by immobilization on heterofunctional epoxy Sepabeads (boronate-epoxy-Sepabeads and chelate-epoxy-Sepabeads). The immobilized preparations displayed increased competitive inhibition constants (K-i) of galactose (boronate-epoxy-Sepabeads, 12.5 mM and chelate-epoxy-Sepabeads, 11.7 mM), whilst the enzyme KM (lactose) only doubled its value. A significant increment of the non-competitive constant was also found (by around a two-fold factor).These increments of the inhibition constants greatly impact on the industrial performance of the enzyme. Thus, while using soluble enzyme in the hydrolysis of 5% lactose, the reaction stopped at around 90% hydrolysis, both immobilized preparations to reached hydrolysis yields higher than 99%. These immobilized forms of beta-galactosidase could be used in the total hydrolysis of lactose in milk or dairy whey even at 70 degreesC. (C) 2003 Elsevier Science Inc. All rights reserved.