N-Acetyl-L-tryptophan or N-Acetyltryptophan, belongs to the class of organic compounds known as N-acyl-alpha amino acids. N-acyl-alpha amino acids are compounds containing an alpha amino acid which bears an acyl group at its terminal nitrogen atom. N-Acetyltryptophan can also be classified as an alpha amino acid or a derivatized alpha amino acid. Technically, N-Acetyltryptophan is a biologically available N-terminal capped form of the proteinogenic alpha amino acid L-tryptophan. N-acetyl amino acids can be produced either via direct synthesis of specific N-acetyltransferases or via the proteolytic degradation of N-acetylated proteins by specific hydrolases. N-terminal acetylation of proteins is a widespread and highly conserved process in eukaryotes that is involved in protection and stability of proteins (PMID: 16465618).  About 85% of all human proteins and 68% of all yeast proteins are acetylated at their N-terminus (PMID: 21750686). Several proteins from prokaryotes and archaea are also modified by N-terminal acetylation. The majority of eukaryotic N-terminal-acetylation reactions occur through N-acetyltransferase enzymes or NAT‚Äôs (PMID: 30054468).  These enzymes consist of three main oligomeric complexes NatA, NatB, and NatC, which are composed of at least a unique catalytic subunit and one unique ribosomal anchor. The substrate specificities of different NAT enzymes are mainly determined by the identities of the first two N-terminal residues of the target protein. The human NatA complex co-translationally acetylates N-termini that bear a small amino acid (A, S, T, C, and occasionally V and G) (PMID: 30054468). NatA also exists in a monomeric state and can post-translationally acetylate acidic N-termini residues (D-, E-). NatB and NatC acetylate N-terminal methionine with further specificity determined by the identity of the second amino acid.  N-acetylated amino acids, such as N-acetyltryptophan can be released by an N-acylpeptide hydrolase from peptides generated by proteolytic degradation (PMID: 16465618). In addition to the NAT enzymes and protein-based acetylation, N-acetylation of free tryptophan can also occur. Many N-acetylamino acids, including N-acetyltryptophan are classified as uremic toxins if present in high abundance in the serum or plasma (PMID: 26317986; PMID: 20613759). Uremic toxins are a diverse group of endogenously produced molecules that, if not properly cleared or eliminated by the kidneys, can cause kidney damage, cardiovascular disease and neurological deficits (PMID: 18287557). N-Acetyltryptophan has also been used as a protein stabilizer. It prevents protein molecules from oxidative degradation by scavenging oxygen dissolved in protein solutions (PMID: 21903216 ). N-Acetyltryptophan has been identified as a catabolite of tryptophan generated by the gut microbiota. After absorption through the intestinal epithelium, tryptophan catabolites enter the bloodstream and are later excreted in the urine (PMID: 28916042). N-Acetyltryptophan is an inhibitor of cytochrome c release and an antagonist of the neurokinin 1 receptor (NK-1R). These inhibitory effects are thought have a useful role in neuroprotection. For instance, in mouse models of amyotrophic lateral sclerosis (ALS) the administration of N-Acetyltryptophan has been shown delay disease onset, extend survival, and ameliorate deterioration in motor performance ALS transgenic mice (PMID: 25986728). N-acetyltryptophan has been shown to significantly reduce blood-brain barrier permeability and improve functional outcome in rat models of traumatic brain injury (PMID: 29256408). N-Acetyltryptophan has also been shown to have a role in preventing hepatic ischemia-reperfusion injury.  This is thought to occur through de-activation of the RIP2/caspase/IL-1beta signaling pathway (PMID: 31184936).