Lysine
Lysine (abbreviated as Lys or K) is an -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.
Lysine is a base, as are arginine and histidine. The -amino group often participates in hydrogen bonding and as a general base in catalysis. Common posttranslational modifications include methylation of the -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.

# Biosynthesis
As an essential amino acid, lysine is not synthesized in animals, hence it must be ingested as lysine or lysine-containing proteins.  In plants and microorganisms, it is synthesized from aspartic acid, which is first converted to -aspartyl-semialdehyde.  Cyclization gives dihydropicolinate, which is reduced to 1-piperidine-2,6-dicarboxylate.  Ring-opening of this heterocycle gives a series of derivatives of pimelic acid, ultimately affording lysine.  Enzymes involved in this biosynthesis include:
- Aspartokinase
- -aspartate semialdehyde dehydrogenase
- Dihydropicolinate synthase
- 1-piperdine-2,6-dicarboxylate dehydrogenase
- N-succinyl-2-amino-6ketopimelate synthase
- Succinyl diaminopimelate aminotransferase
- Succinyl diaminopimelate desuccinylase
- Diaminopimelate epimerase
- Diaminopimelate decarboxylase

# Metabolism
Lysine is metabolised in mammals to give acetyl-CoA, via an initial transamination with -ketoglutarate. The bacterial degradation of lysine yields cadaverine by decarboxylation.

# Synthesis
Synthetic, racemic lysine has long been known.  A practical synthesis starts from caprolactam.

# Dietary sources
The  human nutritional requirement is 11.5 g daily. It is the limiting amino acid (the essential amino acid found in the smallest quantity in the particular foodstuff) in all cereal grains, but is plentiful in all pulses (legumes). Plants that contain significant amounts of lysine include:
- Buffalo Gourd (10,13033,000 ppm) in seed
- Berro, Watercress (1,34026,800 ppm) in herb.
- Soybean (24,29026,560 ppm) in seed.
- Carob, Locust Bean, St.John's-Bread (26,320 ppm) in seed;
- Common Bean (Black Bean, Dwarf Bean, Field Bean, Flageolet Bean, French Bean, Garden Bean, Green Bean, Haricot, Haricot Bean, Haricot Vert, Kidney Bean, Navy Bean, Pop Bean, Popping Bean, Snap Bean, String Bean, Wax Bean) (2,39025,700 ppm) in sprout seedling;
- Ben Nut, Benzolive Tree, Jacinto (Sp.), Moringa (aka Drumstick Tree, Horseradish Tree, Ben Oil Tree), West Indian Ben (5,37025,165 ppm) in shoot.
- Lentil (7,12023,735 ppm) in sprout seedling.
- Asparagus Pea, Winged Bean (aka Goa Bean) (21,36023,304 ppm) in seed.
- Fat Hen (3,54022,550 ppm) in seed.
- Lentil (19,57022,035 ppm) in seed.
- White Lupin (19,33021,585 ppm) in seed.
- Black Caraway, Black Cumin, Fennel-Flower, Nutmeg-Flower, Roman Coriander (16,20020,700 ppm) in seed.
- Spinach (1,74020,664 ppm).
- Amaranth, Quinoa
Good sources of lysine are foods rich in protein including meat (specifically red meat, pork, and poultry), cheese (particularly parmesan), certain fish (such as cod and sardines), and eggs.
Nuts are particularly a bad source for lysine.#REDIRECT ]

# Properties
L-Lysine is a necessary building block for all protein in the body. L-Lysine plays a major role in calcium absorption; building muscle protein; recovering from surgery or sports injuries; and the body's production of hormones, enzymes, and antibodies.

# Clinical significance
It has been suggested that lysine may be beneficial for those with herpes simplex infections. However, more research is needed to fully substantiate this claim.  For more information, refer to Herpes simplex - Lysine.
Lysine can help to alleviate the symptoms of coldsores.  They help to speed up the healing process if taken immediately.

# Trivia
In the movie Jurassic Park the dinosaurs were genetically altered so they could not produce lysine (the "lysine contingency"). This was supposed to prevent the dinosaurs from leaving the park.