L-Lysine (abbreviated as Lys or K) is an alpha-amino acid with the chemical formula HO2CCH(NH2)(CH2)4NH2. This amino acid is an essential amino acid, which means that humans cannot synthesize it. Its codons are AAA and AAG. L-Lysine is a base, as are arginine and histidine. The epsilon-amino group often participates in hydrogen bonding and as a general base in catalysis. Common posttranslational modifications include methylation of the epsilon-amino group, giving methyl-, dimethyl-, and trimethyllysine. The latter occurs in calmodulin. Other posttranslational modifications include acetylation. Collagen contains hydroxylysine which is derived from lysine by lysyl hydroxylase. O-Glycosylation of lysine residues in the endoplasmic reticulum or Golgi apparatus is used to mark certain proteins for secretion from the cell.L-lysine is an essential amino acid. Normal requirements for lysine have been found to be about 8 g per day or 12 mg/kg in adults. Children and infants need more- 44 mg/kg

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