Thiamine Biosynthesis in Escherichia coli: Identification of the Intermediate and By-Product Derived from Tyrosine

Thiamine is an essential cofactor in many metabolic pathways and is required by all living organisms. The biosynthesis of thiamine phosphate is convergent, linking two independently biosynthesized heterocyclic precursors in the final step. In this paper, we elucidate the reaction products formed in vitro from the ThiGH complex, demonstrating that the aromatic by-product derived from the side chain of tyrosine is p-cresol and the remaining fragment of tyrosine yields glyoxylate, the expected product of in situ hydrolysis of dehydroglycine. Finally, these experiments are shown to be relevant to in vivo metabolism by the detection of p-cresol in E. coli that are expressing ThiH.