Modulation of the catalytic properties of multimeric β-galactosidase from E. coli by using different immobilization protocols

Different immobilized preparations of the β-galactosidase from E. coli were obtained by using different supports and immobilization strategies (bearing glyoxyl, epoxy, or BrCN groups or by glutaraldehyde crosslinking on matrices containing primary amino groups). In all cases, the immobilization yield was 100% with activity recoveries between more than 50% and almost 100% (using o-NPG as substrate). The immobilization varied the specificity of the enzyme. While the enzyme immobilized on Eupergit 250L decreased its activity to a 70% in the hydrolysis of o-NPG, this immobilized preparation exhibited an increment in the enzyme activity against lactose by a factor of 2. The different derivatives exhibited very different synthetic activity/hydrolytic activity ratios (Vs/Vh) in transglycosylation reactions and was strongly modulated by the experimental conditions. Thus, Vs/Vh values lower than 0.1 were obtained with the enzyme immobilized on BrCN at 4 °C and pH 7, while the soluble enzyme gave a ratio value of 0.46 and the enzyme immobilized on Eupergit 250L gave a ratio of 0.8. Under similar conditions, again experimental conditions presented different effects on the different enzyme preparations: Eupergit C immobilized enzyme and soluble enzyme improve the Vs/Vh ratio when decreasing the temperature while BrCN immobilized enzyme suffered a great decrease in this ratio. These results suggest that the properties of this enzyme may be strongly modulated during immobilization, and that using a battery of immobilization strategies is possible to prepare immobilized enzymes with very different properties.