Overview: Tryptophan is an essential amino acid with diverse biological role and function in human body. Here are some key aspects of the biological function of tryptophan:

1. Protein Synthesis: Tryptophan is one of the 20 standard amino acid used by cells to build proteins and is incorporated into polypeptide chains during translation.

2. Precursor for Serotonin Synthesis: Tryptophan serves as precursor for serotonin, a neurotransmitter involved in mood regulation, sleep-wake cycle, appetite, and emotional well-being. Within neurons, tryptophan is converted into 5-hydroxytryptophan (5-HTP) by the enzyme tryptophan hydroxylase.

3. Niacin (Vitamin B3) Synthesis: Tryptophan is a precursor for niacin (nicotinic acid or nicotinamide) synthesis. Through the kynurenine pathway, tryptophan is metabolized into nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide in cellular energy production and redox reaction.

4. Kynurenine Pathways : Tryptophan metabolism also occurs through the kynurenine pathway, leading to the production of various metabolites such as kynurenine acid, quinolinic acid, and picolinic acid. These metabolites have immunomodulatory, neuroprotective, and neurotoxic effects, influencing inflammation, oxidative stress, and neurotransmitter balance.

5. Melatonin Production: Tryptophan is precursor for melatonin synthesis, a hormone that regulate the sleep-wake cycles and circadian rhythms. It is converted to serotonin, which is then transform to melatonin during nighttime.

6. Regulation of immune response: Tryptophan metabolism, through the kynurenine pathway can modulate immune response, influencing immune tolerance, inflammation, and immune system regulation.

7. Antioxidants Properties :Tryptophan and its metabolite have antioxidants properties, helping to neutralize free radicals and oxidative stress in cells and tissue.

8. Neurotransmitter Balance : Tryptophan availability, along with other amino acids like tyrosine, phenylalanine, and methionine, influences neurotransmitter balance in brain. Alterations in amino acids ratios can impact neurotransmitters synthesis, affecting mood, cognitive, and neurological functions.

These biological functions highlight the importance of tryptophan in protein synthesis, neurotransmitters production, immune regulation, antioxidants defense, and overall physiological processes within the body.