What is Tryptophan?
Tryptophan is an α-amino acid which is used in the biosynthesis of proteins and is encoded by the codon UGG. It is denoted as Trp or W. It consists of an α-carboxylic acid group, α-amino group, and a side chain indole, therefore making it a non-polar aromatic amino acid. It is required for humans but cannot be synthesized by the body. Therefore, it is taken through diet. It acts as a precursor to the hormone melatonin, neurotransmitter serotonin, and vitamin B3.
Physical and chemical properties of Tryptophan
It is a solid slightly yellowish-white in colour with no odour and flat taste. Its chemical formula is C11H12N2O2 and has a molar mass of 204.229 g·mol−1. It is soluble in hot alcohol, alkali hydroxides, acetic acid, ethanol but insoluble in ethyl ether and chloroform. The melting point of Trp is 290.5 dec °C and has a pKa value equal to 7.38 at 25 °C.
Functions of Tryptophan
Tryptophan functions as a biochemical precursor for some compounds that we have discussed below:
- A neurotransmitter such as serotonin is synthesized by tryptophan hydroxylase.
- A neurohormone such as elatonin is synthesized from serotonin.
- Niacin also referred to as vitamin B3, is synthesized from tryptophan through quinolinic and kynurenine acids.
- A class of phytohormones such as auxins are synthesized from tryptophan.
Production of Tryptophan
It is not synthesized from simpler substances in animals and humans. It is required in the diet in the form of tryptophan-containing proteins as it is an essential amino acid. Usually, microorganisms and plants commonly synthesize tryptophan from anthranilate or shikimic acid.
- Anthranilate undergoes condensation with PRPP (phosphoribosylpyrophosphate) to obtain pyrophosphate as a by-product.
- By opening the ring of the ribose moiety it is exposed to reductive decarboxylation to generate indole-3-glycerol phosphate.
- Further, it is transformed into indole.
- In the last step, catalyzation of tryptophan formation from indole and serine (amino acid) by tryptophan synthase takes place.
Isolation and Interactions of tryptophan
Frederick Hopkins was the first to report the isolation of tryptophan in the year 1901. When Try is consumed in a dietary supplement tablet form with antidepressants of the SSRI or MAOI class drugs, it can cause serotonin syndrome.
It is found in most dietary proteins or protein-based foods. It is present in large amounts in oats, milk, cottage cheese, eggs, poultry, chickpeas, sunflower seeds, pumpkin seeds, spirulina, chocolate, dried dates, yoghurt, red meat, fish, peanuts, sesame, almonds, and buckwheat.
Consuming tryptophan supplementation causes nausea, drowsiness, headache, blurred vision, euphoria, involuntary eye movements, diarrhoea, lightheadedness, dry mouth, and sedation.
Tryptophan is a significant intrinsic fluorescent probe which can be used to determine the nature of the microenvironment around tryptophan residues.