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When enzymes are to be used in organic media, noncovalent immobilization methods are often used because enzymes in general are insoluble in those media. Usually, immobi-lization increases the observed catalytic activity drastically as compared with nonimmobilized enzyme powder. The main reason is that immobilization spreads the enzyme on a relatively large area, which facilitates the mass transfer of substrates and products. The morphology of the support material is thus of crucial importance. In many applications, a monolayer of enzyme on the support provides catalysts with good activity. In general, the enzyme is first present in an aqueous solution and water is then removed using a drying procedure. Simple and effective methods for the adsorption of lipase on porous polypropylene and deposition of a -chymotrypsin on Celite ® are presented in this chapter. [ABSTRACT FROM AUTHOR]

The catalytic activity of an enzyme in an organic medium depends on its hydration state. Of the different possible ways to quantify the amount of water present in the reaction mixture, the water activity has been shown to be preferable because it correlates well with the hydration state of the enzyme (compare Chapter 11). If other ways are used to quantify water in these systems, the results are often more difficult to interpret. In a typical example, the dependence of the enzymatic activity on the solvent was studied. The optimal water concentration varied within a wide range in the solvents studied, but the optimal water activity was virtually the same in all solvents (1). Similarly, the optimal water activity was the same when different support materials were used for immobilization of the enzyme but the optimal water concentration varied depending on the water-absorbing capacity of the support (2). [ABSTRACT FROM AUTHOR]