![]() ![]() Lactobacillaceae ( Lactobacillus s.l.) species metabolize tryptophan into indole-3-aldehyde (I3A) which acts on the aryl hydrocarbon receptor (AhR) in intestinal immune cells, in turn increasing interleukin-22 (IL-22) production. Following absorption from the intestine and distribution to the brain, IPA confers a neuroprotective effect against cerebral ischemia and Alzheimer's disease. IPA binds to the pregnane X receptor (PXR) in intestinal cells, thereby facilitating mucosal homeostasis and barrier function. Clostridium sporogenes metabolizes tryptophan into indole and subsequently 3-indolepropionic acid (IPA), a highly potent neuroprotective antioxidant that scavenges hydroxyl radicals. Indole is produced from tryptophan by bacteria that express tryptophanase. This diagram shows the biosynthesis of bioactive compounds ( indole and certain other derivatives) from tryptophan by bacteria in the gut. This permits tightly regulated and rapid responses to changes in the cell's internal and external tryptophan levels. So high levels of tryptophan prevent tryptophan synthesis through a negative feedback loop, and when the cell's tryptophan levels go down again, transcription from the trp operon resumes. Binding of this repressor to the tryptophan operon prevents transcription of downstream DNA that codes for the enzymes involved in the biosynthesis of tryptophan. ![]() ![]() In bacteria that synthesize tryptophan, high cellular levels of this amino acid activate a repressor protein, which binds to the trp operon. The disorder fructose malabsorption causes improper absorption of tryptophan in the intestine, reduced levels of tryptophan in the blood, and depression. Auxins (a class of phytohormones) are synthesized from tryptophan.Niacin, also known as vitamin B 3, is synthesized from tryptophan via kynurenine and quinolinic acids.The kynurenine pathway of tryptophan catabolism is altered in several diseases, including psychiatric disorders such as schizophrenia, major depressive disorder, and bipolar disorder. Two enzymes, namely indoleamine 2,3-dioxygenase (IDO) in the immune system and the brain, and tryptophan 2,3-dioxygenase (TDO) in the liver, are responsible for the synthesis of kynurenine from tryptophan. Kynurenine, to which tryptophan is mainly (more than 95%) metabolized.Melatonin (a neurohormone) is in turn synthesized from serotonin, via N-acetyltransferase and 5-hydroxyindole-O-methyltransferase enzymes.Serotonin (a neurotransmitter), synthesized by tryptophan hydroxylase.In addition, tryptophan functions as a biochemical precursor for the following compounds: Tryptophan, along with other aromatic amino acids, is also important in glycan-protein interactions. ![]() For instance, tryptophan and tyrosine residues play special roles in "anchoring" membrane proteins within the cell membrane. Tryptophan is among the less common amino acids found in proteins, but it plays important structural or functional roles whenever it occurs. Transformed functional groups after each chemical reaction are highlighted in red.Īmino acids, including tryptophan, are used as building blocks in protein biosynthesis, and proteins are required to sustain life. Function Metabolism of l-tryptophan into serotonin and melatonin (left) and niacin (right). In 2023, the emission spectrum of tryptophan was discovered in the interstellar gas of the star cluster IC 348. Humans and many animals cannot synthesize tryptophan: they need to obtain it through their diet, making it an essential amino acid. Like other amino acids, tryptophan is a zwitterion at physiological pH where the amino group is protonated (– NH +ģ pK a = 9.39) and the carboxylic acid is deprotonated ( –COO − pK a = 2.38). Tryptophan is also a precursor to the neurotransmitter serotonin, the hormone melatonin, and vitamin B3. Tryptophan contains an α-amino group, an α- carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromatic beta carbon substituent. Is an α- amino acid that is used in the biosynthesis of proteins. ![]()
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