Effect of a Successive Feed of Melt Indole on the Production of
L-Tryptophan by Tryptophan Synthase

Takatoshi SETO* and Makoto IMANARI

Yokohama Research Center, Mitsubishi Chemical Co., Ltd.; 1000 Kamoshidacho,
Aoba-ku, Yokohama-shi 227-8502 Japan
Kurosaki Plant, Mitsubishi Chemical Co., Ltd.; Kurosaki, Yawatanishi-ku,
Kitakyushu-shi 806-0004 Japan

A process of L-tryptophan (Trp) synthesis from indole (Ind) and L-serine by Escherichia coli transformant cells including tryptophan synthase was investigated. Usually, the reaction is strongly inhibited by Ind and Trp accumulated. Therefore, we constructed a new system of successively feeding melt Ind into the reactor. Yield of Trp formation with this method was much larger than that with a blanket feed of Ind. In a reactor of 1 L, a concentration of Trp formed=92 g L−1 and an amount of Trp formation per amount of cells=9.2 g(g-cell)−1 were attained through 3-h reaction. The velocity of feeding Ind per amount of cells had the least upper bound in keeping Trp formation. Rate equations were constructed based on a model where the active enzyme was changed into an inactive one through the reaction. The hypothetical equations successfully explained the reaction of Trp synthesis from Ind and L-serine.

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