Biosynthesis and industrial production
As an ‘essential amino acid’, tryptophan is not synthesized from more basic substances in humans and other animals, who must ingest tryptophan or tryptophan-containing proteins. Plants and microorganisms commonly synthesize tryptophan from shikimic acid or anthranilate by the following process: anthranilate condenses with phosphoribosylpyrophosphate (PRPP), generating pyrophosphate as a by-product. The ring of the ribose moiety is opened and subjected to reductive decarboxylation, producing indole-3-glycerinephosphate; this, in turn, is transformed into indole. In the last step, tryptophan synthase catalyzes the formation of tryptophan from indole and the amino acid serine.
The industrial production of tryptophan is also biosynthetic and is based on the fermentation of serine and indole using either wild-type or genetically modified bacteria such as B. amyloliquefaciens, B. subtilis, C. glutamicum or E. coli. These strains carry either mutations that prevent the “re-uptake” of aromatic amino acids or multiple/overexpressed trp operons. The conversion is catalyzed by the enzyme tryptophan synthase.