Oxidations with isolated and cell-bound dehydrogenases and oxidases

Oxidations catalyzed by microbial dehydrogenases and oxidases allow for transformation of different molecules (primary and secondary alcohols, aldehydes, amines, saturated compounds) with high chemo-, regio- and enantioselectivity. Although only few bio-oxidations have been developed on large scale, the use of dehydrogenases and oxidases can be seen as a complementary tool to conventional synthetic methods. This review shows the advantages and the limitations of bio-oxidations catalyzed by whole microbial cells and/or isolated enzymes, with particular emphasis on the problem of cofactor recycling. The representative examples have been chosen trying to highlight how the problems of low selectivity or productivity can be overcome by using different techniques, such as the use of isolated enzymes and addition of coenzymes coupled with systems for regeneration of the coenzymes, genetic modification of the microorganism for knocking-out the degrading enzymes, recombination of the oxidative enzyme of interest in hosts with no overmetabolism, in situ extraction of the product, employment of microorganisms with "incomplete" oxidative metabolism, use of synthetic substrates leading to product not further modifiable.