Enantiospecific biocatalyst

Transaminases possess many features appropriate for effident biocatalysts, such as high turnover numbers and no requirement for external recycling of the co-factor. Because of the wide substrate tolerance of many amino transferases such as tyrosine amino transferase and branched-chain amino transferases from E. coU, these enzymes have been largely employed in the enantiospecific preparation of non-proteinogenic amino acids. These include straight-chain alkyl, diadd, branched-chain, aromatic, and bifunctional amino adds [65]. 

Very recently, however, a remarkably improved whole-cell biocatalyst coexpressing an L-carbamoylase, a hydantoin racemase, and an L-hydantoinase has been developed which showed a 50-fold higher productivity and is suitable for large-scale applications [17]. A prerequisite of this efficient whole-cell biocatalyst, which is applied at Degussa, was the successful inversion of the enantiospecificity of a previously D-selective hydantoinase by means of directed evolution [18]. These improvements have already been confirmed at a m3-scale using a batch reactor concept [17]. 

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