Dependence of Lipase Activity on Water Content and Enzyme Concentration in Reverse Micelles

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Abstract
The activity of Candida rugosa lipase (EC 3.1.1.3) in reverse micelles has been measured at various concentrations of water and enzyme with the aim of answering the question, why is the enzyme activity affected by the molar ratio of water to surfactant (w0 = [H2O]/[Surfactant])? In the low range of water content (below w0 ≈ 6), the activity increases with increasing water content, indicating the requirement of a minimum amount of water for the full expression of enzymatic activity. The minimal w0-value for obtaining maximal activity depends on the enzyme concentration: The higher the enzyme concentration, the higher w0, max. In addition, it was found that, at least for the case of Candida rugosa lipase, the measured dependence of enzyme activity on w0 does not represent a true chemical equilibrium. Changing the w0-value during the reaction does not change the activity as expected on the basis of the w0-activity profile obtained for single w0 point measurements. All these observations, however, cannot be directly generalized to all enzymes in reverse micelles, due to the peculiarity of lipase. In particular, the enzyme seems to inactivate irreversibly during the solubilization process.