Abstract
Abstract l-Cysteine is widely used in food, medicine, and cosmetics. In this study, a recombinant Escherichia coli whole-cell system with tryptophan synthase was used to complete the biological transformation of l-serine to l-cysteine, and bioconversion of l-cysteine was investigated by tryptophan synthase. The biotransformation of l-cysteine was optimized by response surface methodology. The optimal conditions obtained are 0.13 mol·L−1 l-serine, 75 min, 130 W ultrasound operation, where the V max of tryptophan synthase is 25.27 ± 0.16 (mmol·h−1·(g-cells)−1). The V max of tryptophan synthase for the biosynthesis without ultrasound is 12.91 ± 0.34 (mmol·h−1·(g-cells)−1). Kinetic analysis of the recombinant Escherichia coli whole-cell system with tryptophan synthase also showed that under the ultrasound treatment, the K m values of l-cysteine biosynthesis increase from 1.342 ± 0.11 mM for the shaking biotransformation to 2.555 ± 0.13 mM for ultrasound operation. The yield of l-cysteine reached 91% after 75 min of treatment after 130 W ultrasound, which is 1.9-fold higher than no ultrasound.
Highlights
L-Cysteine is an amino acid that contains sulphydryl groups, and it is used in medicine, cosmetics, and food [1]
L-Cysteine was synthesized from L-serine and sodium bisulphide using tryptophan synthase by response surface methodology (RSM) under ultrasound treatment
The reaction of the recombinant E. coli whole-cell system with tryptophan synthase was executed in an ultrasonic tank with a power series ranging from 60 to 200 W (SB-120D, China)
Summary
L-Cysteine is an amino acid that contains sulphydryl groups, and it is used in medicine, cosmetics, and food [1]. The trp B and trp A genes (or trp BA genes) coexist in the tryptophan operon of the E. coli genome. The activities of both subunits increase upon complex formation and are further regulated by an intricate and well-studied allosteric mechanism. The rate of L-cysteine formation from L-serine and sodium hydrosulphide with tryptophan synthase was 47%. The yield of L-cysteine synthesized by tryptophan synthase was low. The synthesis of L-cysteine by ultrasound-assisted tryptophan synthase was rare. Our innovations gave a high yield of L-cysteine with ultrasound-assisted tryptophan synthase. L-Cysteine was synthesized from L-serine and sodium bisulphide using tryptophan synthase by response surface methodology (RSM) under ultrasound treatment
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