Abstract
A new process for tryptophan production was established using a lipoic acid auxotrophic mutant, Enterobacter aerogenes L-12, which has both pyruvic acid productivity and tryptophanase activity. The process consists of the production of pyruvic acid from glucose by the washed cells and the subsequent conversion of the acid to tryptophan by the tryptophanase itself in the presence of indole and NH4Cl.
To prepare washed cells of which the tryptophanase activity and the pyruvic acid productivity were both high, it was best to culture the strain in a medium containing 1% Polypepton, 0.2% glucose, 3 μg/l DL-lipoic acid, 0.05% L-tryptophan, and mineral salts. The optimum composition of the reaction mixture for the pyruvic acid production by the washed cells was established. Under these conditions, 17 g/l of pyruvic acid was accumulated from 5% glucose after 36 hr of incubation. Thus, the conversion of the pyruvic acid to tryptophan was done by adding indole, NH4Cl, pyridoxal-5'-phosphate, Triton X-100, and KOH to adjust the pH to 9.0 to the above reaction mixture. As a result, the pyruvic acid was rapidly converted to tryptophan, and the concentration of 14 g/l was obtained after 36 hr (total 72 hr).
