N-alpha-Acetyl-L-lysine also known as Nalpha-Acetyllysine, 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-alpha-Acetyl-L-lysine can also be classified as an alpha amino acid or a derivatized alpha amino acid. Technically, N-alpha-Acetyl-L-lysine is a biologically available N-terminal capped form of the proteinogenic alpha amino acid L-lysine. Unlike L-lysine, acetylated lysine derivatives such as N-alpha-Acetyl-L-lysine are zwitterionic compounds. These are molecules that contains an equal number of positively- and negatively-charged functional groups. N-alpha-Acetyl-L-lysine is found naturally in eukaryotes ranging from yeast to plants to humans. 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-alpha-Acetyl-L-lysine 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 lysine can also occur. In particular, N-alpha-Acetyl-L-lysine can be biosynthesized from L-lysine and acetyl-CoA via the enzyme known as Lysine N-acetyltransferase.  Individuals with hyperlysinaemia due to L-lysine alpha-ketoglutarate reductase deficiency will excrete high levels of N-alpha-Acetyl-L-lysine in their urine (PMID: 116084). L-lysine alpha-ketoglutarate reductase deficiency, if untreated, can lead to neurological and behavioral deficits (PMID: 116084). Many N-acetylamino acids 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).