The Tryptophan → Ommochrome Pathway in Insects

TLDR: In this article, the role of ommochromes in insect life and the relation of tryptophan metabolism to insect development is discussed, and a physiological understanding of this pathway in insects is presented.

Abstract: Publisher Summary This chapter assembles data, which contribute to a physiological understanding of this pathway in insects, to appraise the role of ommochromes in insect life, and the relation of tryptophan metabolism to insect development. Tryptophan is an outstanding amino acid. It has the highest molecular weight of all amino acids occurring in proteins, and comprises, in its indolyl moiety, a system capable of donating electrons and; therefore, liable to form complexes with a range of other molecules. Molecular interactions have been observed between tryptophan and nucleic acids, and a variety of other molecules of biological importance. Organisms have taken advantage of the potentialities of this molecule and have transformed it into a wide range of biologically active compounds. In these, either the indole ring or its benzene nucleus are retained, the latter also being recast into the pyridine ring. In insects, a major product of tryptophan degradation is a group of 10 to 15 pigments, the ommochromes. Being brownish-yellow, bright red or dark violet-purple, these pigments produce the deep tinge of insect eyes and contribute to the brilliant coloration of many species.