Effect of beta-galactosidase hydration on alcoholysis reaction in organic one-phase liquid systems

Alcoholysis reactions were performed in organic one-phase liquid systems wi th E. coli beta -galactosidase to produce heptyl-beta -galactoside from lac tose and 1-heptanol. The reaction rate was highly dependent on the amount o f water solubilized in the alcohol. A larger amount of water led to a syste m of two liquid phases in which the alcoholysis rate was 73% faster than in the one-phase system. No hydrolysis reaction of either lactose or product was observed in one-phase liquid systems up to 20 h, independent of the wat er content. Solubility of lactose in the organic phase increased with the w ater content in the system and the reaction followed the Michaelis-Menten m odel. Water activity was calculated for heptanol containing different amoun ts of water and the obtained values were used to estimate the hydration of p-galactosidase from known models. Enzyme activity correlated with sorbed w ater, similar to the behavior reported for lysozyme in low water environmen ts. It is concluded that water contribution to enzyme hydration dominates t he rate of reaction compared to its effect on lactose solubilization. (C) 2 000 John Wiley & Sons, Inc.