Enzymatic Synthesis of Peptide in Water-Miscible Organic Solvent/Supercritical Carbon Dioxide

Enzymatic catalysis in nonaqueous media (see Chapters 23 and 24) has revealed some beneficial features of enzymes such as enhanced thermostability and altered specificity, and thermodynamic equilibria are shifted to favor synthesis over hydrolysis, e.g., esterification and peptide formation (1 –4 ). Enzymatic reactions in water-miscible organic solvents have the advantage of the solubility of a variety of substrates, including amino acid derivatives, which are often poorly soluble in nonpolar solvents (5 ). However, as the addition of a certain amount of exogenous water into a water-miscible organic solvent is required to obtain the enzyme activity, the yield of product at equilibrium is expected to be less than that in dry solvents, and, moreover, the stability of the enzyme is reduced by the autolysis. On the other hand, as the enzyme is insoluble in a nonaqueous medium, and is suspended, the enzymatic reaction tends to be a diffusion-controlled reaction (4 ,6 ).