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

Abstract

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 in to 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 pe r 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.