Biosynthesis of Aromatic Amino Acids

The genes and operons responsible for aromatic amino acid biosynthesis are organized differently in different bacterial species, reflecting different evolutionary histories and possibly the functional and regulatory constraints experienced by each species. This chapter describes the genes, enzymes, and reactions of aromatic amino acid biosynthesis in B. subtilis. The chromosomal locations of the various operons are summarized in this chapter. The chapter also presents current understanding of regulation of aromatic amino acid metabolism in this bacillus. It compares the structural, functional, and regulatory features of aromatic amino acid metabolism in B. subtilis with that of E. coli. In early in vivo studies of aromatic amino acid biosynthesis in B. subtilis, it was observed that histidine, tyrosine, or tryptophan synthesis influenced the cellular levels of enzymes involved in the biosynthesis of the three amino acids ((phenylalanine, tyrosine, and tryptophan). B. subtilis forms a permease that transports phenyl alanine and tyrosine but not tryptophan or any other amino acid. Transport of phenylalanine and tyrosine by this system has been shown to be competitive.