Application of the tryptophanase promoter to high expression of the tryptophan synthase gene inEscherichia coli

Abstract

The application of an inducible regulation system using the tryptophanase operon promoter (TPase promoter; Ptna) was examined for its high expression of the tryptophan synthase (TS) gene in Escherichia coli. The main problem in the application of Ptna for industrial purposes is catabolite repression by glucose, since glucose is the most abundant carbon source. However, this problem could be avoided by changing glucose to an organic acid, such as succinate, fumarate, malate and acetate, in the course of cultivation after glucose initially added was completely consumed. Under these conditions, L-tryptophan was also used to induce tryptophan synthase. Thus, the specific activity of TS in E. coli strain no. 168 harbouring pBR322F-Ptna TS was increased 500-fold compared to that of the cultured host strain. About 1 mol L-tryptophan/l reaction mixture was formed from indole and L-serine at 37 degrees C for 3.5 h.

Cloning, nucleotide sequences, and overexpression in Escherichia coli of tandem copies of a tryptophanase gene in an obligately symbiotic thermophile, Symbiobacterium thermophilum

“…Tryptophanase (L-tryptophan indole-lyase; EC 4.1.99.1) is a catabolic enzyme that catalyzes a pyridoxal 5'-phosphatedependent conversion of L-tryptophan to indole, pyruvate, and ammonia through the ao,,-elimination reaction (19,22,24). Tryptophanase is a multifunctional enzyme which catalyzes not only many other a,,B eliminations of various kinds of substrates but also numerous 13-replacement reactions (7,13,14).…”