ABSTRACT
In living cells, water is the predominant solvent. It is therefore not surprising that scientific studies of enzymes have been carried out mainly in aqueous media. Often quite dilute solutions of substrates and enzymes in aqueous buffers have been studied. However, one should bear in mind that high concentrations of proteins, other biopolymers and low molecular weight compounds are present around the enzymes in living cells. Furthermore, some enzymes are associated with membrane structures containing mainly hydrophobic lipids. Accordingly, some of the “nonconventional” reaction media used recently for enzymatic reactions may be as natural for the enzymes as dilute aqueous solutions. Media normally referred to as non-conventional for enzymatic reactions are those containing mainly organic substances (solvents, substrates, products, etc.) or supercritical fluids (Table 9.1). Another type of non-conventional systems uses gaseous reaction media. Common for all these media is that the water content is reduced compared to “conventional media” (aqueous solutions).
