Hydrolytic enzymes amidases/acylases

The use of enzymes and whole cells as catalysts in organic chemistry is described. Emphasis is put on the chemical reactions and the importance of providing enantiopure synthons. In particular kinetics of resolution is in focus. Among the topics covered are enzyme classification, structure and mechanism of action of enzymes. Examples are given on the use of hydrolytic enzymes such as esterases, proteases, lipases, epoxide hydrolases, acylases and amidases both in aqueous and low-water media. Reductions and oxidations are treated both using whole cells and pure enzymes. Moreover, use of enzymes in sngar chemistiy and to prodnce amino acids and peptides are discnssed. 

Alternative hydrolytic enzymes, such as amidases and acylases, have also been employed for the resolution of racemic amines. Unlike lipases, these enzymes are typically not commercially available but they can be isolated from microorganisms. 

This consideration is significant for hydrolytic reactions with hydrolases such as lipases, esterases, and amidases. These include penicillin amidases (synonymous with penicillin acylases) and cephalosporin acylases which are used for hydrolytic cleavage of penicillins and cephalosporins in thousands of tons per year [98]. These hydrolyses have to be performed at a pH-value of 8 which is close to the optimum pH of the enzyme. Lower pH-values lead to lower reaction rates and reversibility of the reaction, and hence to a significant loss in product formation. Higher pH-values are not advisable owing to the instability of the reaction partners. Moreover, addition of buffers is not accepted because of the costly removal of the buffer components. 

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