Abstract: Enzymatic synthesis of L-tryptophan from L-serine and indole catalyzed by tryptophan synthase from recombinant Escherichia coli DM206 [pET28a-trpBA/BL21(DE3)] in an aqueous/organic biphasic system was carried out. The effects of organic solvents, volume fraction of ethyl acetate, reaction temperature, pH value of the aqueous phase, molar ratio of L-serine to indole, L-serine concentration, surfactants, and enzyme amount were investigated. Ethyl acetate was found to be the best organic solvent for the reaction. The optimal volume fraction of ethyl acetate was 2.5%. The optimal temperature and pH value were 35 ºC and 8, respectively. The optimal molar ratio of L-serine to indole was 1:1.2. The optimal L-serine concentration was 100 mmol/L. The optimal mass fraction of Tween 80 was 0.4%. The optimal enzyme amount was 20 g/L. Under the optimal conditions, bioconversion rate of L-serine reached 95% after 2.5 h in the aqueous/organic biphasic system.

Key words: tryptophan synthase, L-tryptophan, L-serine, indole, ethyl acetate, water