Simple enzymatic procedure for l ‐carnosine synthesis: whole‐cell biocatalysis and efficient biocatalyst recycling

Summary β ‐Peptides and their derivates are usually stable to proteolysis and have an increased half‐life compared with α ‐peptides. Recently, β ‐aminopeptidases were described as a new enzyme class that enabled the enzymatic degradation and formation of β ‐peptides. As an alternative to the existing chemical synthesis routes, the aim of the present work was to develop a whole‐cell biocatalyst for the synthesis and production of β ‐peptides using this enzymatic activity. For the optimization of the reaction system we chose the commercially relevant β , α ‐dipeptide l ‐carnosine ( β ‐alanine‐ l ‐histidine) as model product. We were able to show that different recombinant yeast and bacteria strains, which overexpress a β ‐peptidase, could be used directly as whole‐cell biocatalysts for the synthesis of l ‐carnosine. By optimizing relevant reaction conditions for the best‐performing recombinant Escherichia coli strain, such as pH and substrate concentrations, we obtained high l ‐carnosine yields of up to 71%. Long‐time as well as biocatalyst recycling experiments indicated a high stability of the developed biocatalyst for at least five repeated batches. Application of the recombinant E. coli in a fed‐batch process enabled the accumulation of l ‐carnosine to a concentration of 3.7 g l −1 .