Abstract
The microbial production of d-lysine has been of great interest as a medicinal raw material. Here, a two-step process for d-lysine production from l-lysine by the successive microbial racemization and asymmetric degradation with lysine racemase and decarboxylase was developed. The whole-cell activities of engineered Escherichia coli expressing racemases from the strains Proteus mirabilis (LYR) and Lactobacillus paracasei (AAR) were first investigated comparatively. When the strain BL21-LYR with higher racemization activity was employed, l-lysine was rapidly racemized to give dl-lysine, and the d-lysine yield was approximately 48% after 0.5 h. Next, l-lysine was selectively catabolized to generate cadaverine by lysine decarboxylase. The comparative analysis of the decarboxylation activities of resting whole cells, permeabilized cells, and crude enzyme revealed that the crude enzyme was the best biocatalyst for enantiopure d-lysine production. The reaction temperature, pH, metal ion additive, and pyridoxal 5′-phosphate content of this two-step production process were subsequently optimized. Under optimal conditions, 750.7 mmol/L d-lysine was finally obtained from 1710 mmol/L l-lysine after 1 h of racemization reaction and 0.5 h of decarboxylation reaction. d-lysine yield could reach 48.8% with enantiomeric excess (ee) ≥ 99%.
Highlights
D -Amino acids are being used increasingly used as a starting raw material in the production of valuable pharmaceuticals [1]
We developed two other processes that permeabilized cells, and crude extracts of the strain ATS3 were used as the biocatalysts to compare their effects on D‐lysine extracts of the strain ATS3 were used as the biocatalysts to compare their effects on D-lysine enantiomeric excess (Figure 3)
We have developed a two-step microbial process for high-level conversion of to D-lysine through a lysine racemase and decarboxylase cascade system
Summary
D -Amino acids are being used increasingly used as a starting raw material in the production of valuable pharmaceuticals [1]. D-lysine has been employed for the synthesis of luteinizing-hormone-releasing hormone analog, or as a drug carrier in the form of polylysine [2,3]. Several chemical or biochemical synthesis methods for D-lysine synthesis have been described [3]. D-lysine was successfully prepared from L-lysine by chemical racemization and microbial asymmetric degradation [4]. The chemical racemization of amino acids to prepare DL-amino acids is a complex process and requires severe reaction conditions, such as high temperature, strong acid, or alkali [3,4]. The chemical resolution of DL-amino acids is inefficient with low optical purity of products, and requires expensive chiral resolving agent
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