5: Reduction

This chapter covers enzyme classes that catalyse reduction reactions, including ketoreductases, enoate reductases, carboxylic acid reductases, imine reductases, amino acid dehydrogenases, opine dehydrogenases, amine dehydrogenases and nitro reductases. The chapter is divided into separate sections, each detailing the reduction of a specific functional group, including ketones, aldehydes, carboxylic acids, alkenes, imines, nitro aromatics, sulfoxides, azides, n-oxides and azo compounds. Each section begins with a review of chemical methods of carrying out each transformation, followed by a description of the enzyme classes that are also capable of carrying it out. The substrate scope of each enzyme class, including its chemo-, regio- and stereoselectivity, is discussed and a general mechanism for the enzyme-catalysed reaction is presented. Where appropriate, strategies for co-factor recycling are also included. This should give the reader a rounded understanding of when and how to carry out reduction reactions using enzymes.