1 - The Shikimate Pathway: Biosynthesis of the Aromatic Amino Acids

Abstract

Organisms differ markedly in their ability to carry out the chemical reactions involved in the biosynthesis of the amino acids that are constituents of proteins. Most microorganisms and plants are competent in all such syntheses while most animals lack about half of these capabilities. Among the amino acids that cannot be produced by de novo synthesis in animals are the three aromatic amino acids, namely, L-phenylalanine, L-tyrosine and L-tryptophan. In plants and microorganisms, they are formed by a metabolic process known as the shikimate pathway. (—)-Shikimic acid was first described as a natural product from the plant Illicium religiosum Sieb, by Eykmann in 1885, and it was from the Japanese name of this plant, shikimi-no-ki, that the name shikimic acid was derived. This chapter highlights the shikimate pathway from carbohydrate through chorismate to the aromatic amino acids and other metabolically important compounds. It describes the methodology and identification of intermediates. It also discusses the mechanistic studies of the common pathway and the enzymes involved as catalysts in each of the steps from 3-dehydroquinate to chorismate in the common pathway.