Modelling the alcoholysis reaction of β-galactosidase with butanol in reverse micelles

A theoretical thermodynamic model was applied to predict reverse micelle size in an octane-butanol/cetyl trimethylammonium bromide (CTAB)/water system where the alcoholysis of lactose and ONPG was carded out by β-galactosidase. Solvent concentration regions where the hydrolytic enzyme displayed only alcoholysis were found and assayed. The model allows the description of the experimental results, in terms of micellar concentration and size. It was also possible to define enzyme saturating conditions from the predictions of the empty and filled micelle volumes, which match the experimental results. Optimal conditions of the enzyme in a different system were also predicted introducing a parameter (ω'(o)), which is a water/surfactant molar concentration ratio and independent of the surfactant used. Besides demonstrating the possibility of using β-galactosidase in reverse micelles for alcoholysis reactions with no hydrolysis even at high water content, it was also found that the enzyme is more stable in reverse micelles than in water saturated with butanol or water/butanol mixtures.