Lysine
Essential α-amino acid crucial for protein synthesis and metabolism.
Olaneli · Public domain
Lysine (symbol Lys or K; also L-lysine) is an α-amino acid that serves as a building block for many proteins. Its structure includes an α-amino group, an α-carboxylic acid group, and a side chain; at physiological pH in water, the amino group is protonated, the carboxyl group is deprotonated, and the side chain is partially protonated, classifying it as a basic, charged, aliphatic amino acid. It is encoded by the codons AAA and AAG. The α-carbon is chiral, and while lysine can refer to either enantiomer or a racemic mixture, the biologically active form is L-lysine, where the α-carbon has the S configuration. The human body cannot synthesize lysine, making it an essential nutrient that must be obtained from the diet. In organisms that do synthesize it, two main biosynthetic pathways exist: the diaminopimelate (DAP) pathway and the α-aminoadipate (AAA) pathway, each employing distinct enzymes and substrates. The DAP pathway, found in prokaryotes and plants, begins with a condensation reaction between aspartate-derived L-aspartate semialdehyde and pyruvate, proceeding through several variant routes (acetylase, aminotransferase, dehydrogenase, and succinylase) that converge on meso-diaminopimelate, which is decarboxylated to produce L-lysine. The AAA pathway, present in yeast, fungi, and some protists, involves the condensation of α-ketoglutarate and acetyl-CoA via homocitrate, followed by a series of enzymatic steps to yield α-aminoadipate, which is then converted to lysine. Lysine catabolism most commonly occurs through the saccharopine pathway. In humans, lysine is crucial for proteinogenesis, collagen crosslinking, mineral nutrient uptake, and carnitine production for fatty acid metabolism. It also participates in histone modifications, impacting the epigenome, and its ε-amino group engages in hydrogen bonding and acts as a general base in catalysis. A deficiency can lead to defective connective tissues, impaired fatty acid metabolism, anaemia, and systemic protein-energy deficiency, while an excess from ineffective catabolism can cause severe neurological disorders. Lysine was first isolated in 1889 by Ferdinand Heinrich Edmund Drechsel from casein hydrolysis, and its chemical structure was determined in 1902 by Emil Fischer and Fritz Weigert. The one-letter symbol K was assigned because L was already taken by leucine and M by methionine.
- discovered_by
- Ferdinand Heinrich Edmund Drechsel
- structure_determined_by
- Emil Fischer and Fritz Weigert
- classification
- Basic, charged, aliphatic α-amino acid
- biological_role
- Proteinogenesis, collagen crosslinking, mineral uptake, carnitine production, histone modifications
- deficiency_effects
- Defective connective tissues, impaired fatty acid metabolism, anaemia, systemic protein-energy deficiency
Lore & Background
Lysine is an α-amino acid that serves as a building block for many proteins. It features an α-amino group, an α-carboxylic acid group, and a side chain; at physiological pH in water, the amino group is protonated, the carboxylic acid group is deprotonated, and the side chain is partially protonated, classifying it as a basic, charged, aliphatic amino acid. The α-carbon is chiral, and while lysine can refer to either enantiomer or a racemic mixture, the biologically active form is L-lysine, where the α-carbon is in the S configuration. It is encoded by the codons AAA and AAG. The ε-ammonium group is attached to the fourth carbon from the α-carbon, which is attached to the carboxyl group. Humans cannot synthesize lysine, making it an essential dietary nutrient. In organisms that do produce it, two main biosynthetic pathways exist: the diaminopimelate pathway, found in prokaryotes and plants, and the α-aminoadipate pathway, found in yeast, protists, and higher fungi. Lysine catabolism often occurs via the saccharopine pathway. It plays roles in proteinogenesis, collagen crosslinking, mineral nutrient uptake, and carnitine production for fatty acid metabolism. Lysine is also involved in histone modifications, impacting the epigenome, and its ε-amino group participates in hydrogen bonding and acts as a general base in catalysis. A deficiency can lead to defective connective tissues, impaired fatty acid metabolism, anaemia, and protein-energy deficiency, while an overabundance from ineffective catabolism can cause severe neurological disorders. Lysine was first isolated in 1889 by Ferdinand Heinrich Edmund Drechsel from casein hydrolysis, and its chemical structure was determined by Emil Fischer and Fritz Weigert in 1902. The one-letter symbol K was assigned because L was already taken by leucine.
Reader's Guide
Lysine is essential in humans because the body cannot synthesize it; it must be obtained from the diet. It plays several roles, most importantly in proteinogenesis, but also in the crosslinking of collagen polypeptides, uptake of essential mineral nutrients, and production of carnitine, which is key in fatty acid metabolism. Lysine is also involved in histone modifications, impacting the epigenome. A lack of lysine can lead to defective connective tissues, impaired fatty acid metabolism, anaemia, and systemic protein-energy deficiency. Conversely, an overabundance of lysine due to ineffective catabolism can cause severe neurological disorders. Two main biosynthetic pathways exist in organisms that synthesize lysine: the diaminopimelate pathway (found in prokaryotes and plants) and the α-aminoadipate pathway (found in yeast, protists, and higher fungi). Catabolism primarily occurs via the saccharopine pathway, mainly in the liver mitochondria.
Did You Know?
- The one-letter symbol K was assigned to lysine because L was already taken by leucine, and K is the next letter not used for another common amino acid.
- Lysine contains an ε-ammonium group attached to the fifth carbon (the ε-carbon) from the α-carbon.
- The human body cannot synthesize lysine; it is essential and must be obtained from the diet.
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Frequently Asked Questions
Who is Lysine?
Lysine is a basic, charged, aliphatic α-amino acid that serves as a building block for countless proteins. It is encoded by the codons AAA and AAG and is commonly referenced by its single-letter code K.
What are Lysine's powers/role?
Lysine participates in protein synthesis, collagen crosslinking, mineral uptake, carnitine production, and histone modifications. It gets incorporated into nascent polypeptide chains and can be chemically modified post-translationally to regulate gene expression and structural integrity.
How does Lysine's story end?
Because the human body lacks the metabolic pathway to synthesize it, lysine must be continuously supplied through diet, making it an essential nutrient. Without regular dietary intake, protein assembly and downstream metabolic processes grind to a halt.
Why is Lysine important?
As an essential amino acid, lysine underpins protein construction, stable collagen networks, carnitine biosynthesis, and epigenetic histone modifications. Its absence simultaneously disrupts multiple core cellular pathways, making it irreplaceable in human biochemistry.
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