N-Acetyl-L-tyrosine or N-Acetyltyrosine, 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-Acetyltyrosine can also be classified as an alpha amino acid or a derivatized alpha amino acid. Technically, N-Acetyltyrosine is a biologically available N-terminal capped form of the proteinogenic alpha amino acid L-tyrosine. 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-acetyltyrosine 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 tyrosine can also occur. Many N-acetylamino acids, including N-acetyltyrosine 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-Acetyl-L-tyrosine, has also been associated with several inborn metabolic disorders including tyrosinemia I and aromatic l-amino acid decarboxylase deficiency. N-acetyltyrosine, is used in place of as a tyrosine precursor and administered as a source of nutritional support where oral nutrition is inadequate or cannot be tolerated (PMID: 14621123). N-acetyltyrosine has also been identified as an endogenous stress response factor. Under stress conditions, mitochondria release low levels of reactive oxygen species (ROS), which triggers a cytoprotective response, called "mitohormesis". N-acetyltyrosine has recently been identified as an intrinsic triggering factor of mitohormesis in stressed animals (PMID: 32118349). Interventions and small molecules, which promote formation of reactive oxygen species (ROS), have been shown to increase stress resistance and lifespan of different model organisms. These phenotypes occur only in response to low concentrations of ROS, while higher concentrations of ROS exert opposing effects. In this regard, a stress-dependent increase in N-acetyltyrosine was recently found to occur in insect larvae that had endured high temperatures (i.e. thermal stress). N-acetyltyrosine treatment has also been demonstrated to induce thermotolerance in several tested insect species. N-acetyltyrosine has been identified in the serum of humans as well as mice, and its concentration in mice was shown to be increased by heat stress, with N-acetyltyrosine pretreatment lowering the concentrations of corticosterone and peroxidized lipids in heat stressed mice (PMID: 33617888).