Simple enzymatic procedure for L-carnosine synthesis: whole-cell biocatalysis and efficient biocatalyst recycling

beta-Peptides and their derivates are usually stable to proteolysis and have an increased half-life compared with alpha-peptides. Recently, beta-aminopeptidases were described as a new enzyme class that enabled the enzymatic degradation and formation of beta-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 beta-peptides using this enzymatic activity. For the optimization of the reaction system we chose the commercially relevant beta,alpha-dipeptide L-carnosine (beta-alanine-L-histidine) as model product. We were able to show that different recombinant yeast and bacteria strains, which overexpress a beta-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).