Simple enzymatic procedure for L-carnosine synthesis: whole-cell biocatalysis and efficient biocatalyst recycling.
Bottom Line: β-Peptides and their derivates are usually stable to proteolysis and have an increased half-life compared with α-peptides.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).
Affiliation: Laboratory of Chemical Biotechnology, TU Dortmund, 44221 Dortmund, Germany.Show MeSH
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Mentions: By using this experimental set‐up with a constant feed over 4.5 h, an increase of the l‐carnosine titre (Fig. 8) was possible. The final concentration after complete H‐β‐Ala‐NH2 depletion was 3.7 g l−1, which corresponds to a yield of 65% on H‐β‐Ala‐NH2 (totally 25 mM added). Following the course of l‐carnosine formation shows a constant reaction rate of l‐carnosine for the first 2.5 h, while a steady decrease in the rate is observed afterwards. We assume increased hydrolytic activities on l‐carnosine at higher concentrations, which could be underlined by the fact that the final yield of 65% was lower when compared with batch experiments (71%). Also the consumption of the l‐histidine concentration over time and thus the decrease in the ratio of l‐histidine to H‐β‐Ala‐NH2 can influence l‐carnosine formation. The calculated rate of l‐carnosine formation of 3.3 mmol l−1 h−1 during feeding was slightly higher than during batch experiments (3.1 mmol l−1 h−1), suggesting that the H‐β‐Ala‐NH2 concentration dropped below the initial concentration of 5 mM. However, substrate limitation could be excluded due to additional l‐carnosine formation after 4.5 h, at which time no additional H‐β‐Ala‐NH2 was added. Although a decreased yield was observed, the overall process must also be evaluated in the context of downstream processing and thus the here presented fed‐batch process with an increased product titre might be suitable for l‐carnosine production.
Affiliation: Laboratory of Chemical Biotechnology, TU Dortmund, 44221 Dortmund, Germany.