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Tyrosine (abbreviated as Tyr or Y) or 4-hydroxyphenylalanine, is one of the 20 amino acid
Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
s that are used by cells
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
 to synthesize
Protein biosynthesis

Protein synthesis is the process in which cell build proteins. The term is sometimes used to refer only to protein translation but more often it refers to a multi-step process, beginning with amino acid synthesis and transcription which are then used for translation ....
 protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
s. This is a non-essential amino acid and it is found in casein
Casein

Casein is the predominant phosphoprotein that accounts for nearly 80% of proteins in cow milk and cheese. Milk-clotting proteases act on the soluble portion of the caseins, K-Casein, thus originating an unstable micelle state that results in clot formation....
. Tyrosine has a non-polar/hydrophobic side group (see table, amino acid
Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
). In fact, the word "tyrosine" is from the Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 tyros, meaning cheese
Cheese

Cheese is a food consisting of proteins and fat from milk, usually the milk of cattle, Water Buffalo, goats, or sheep's milk. It is produced by Coagulation of the milk protein casein....
, as it was first discovered in 1846 by German chemist Justus von Liebig
Justus von Liebig

Justus von Liebig was a German chemist who made major contributions to agriculture and biology chemistry, and worked on the organization of organic chemistry....
 in the protein casein from cheese.

e from being a proteogenic amino acid, tyrosine has a special role by virtue of the phenol
Phenol

Phenol, also known as carbolic acid, is a toxic, white crystalline solid with a sweet tarry odor, commonly referred to as a "hospital smell"....
 functionality.






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Tyrosine (abbreviated as Tyr or Y) or 4-hydroxyphenylalanine, is one of the 20 amino acid
Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
s that are used by cells
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
 to synthesize
Protein biosynthesis

Protein synthesis is the process in which cell build proteins. The term is sometimes used to refer only to protein translation but more often it refers to a multi-step process, beginning with amino acid synthesis and transcription which are then used for translation ....
 protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
s. This is a non-essential amino acid and it is found in casein
Casein

Casein is the predominant phosphoprotein that accounts for nearly 80% of proteins in cow milk and cheese. Milk-clotting proteases act on the soluble portion of the caseins, K-Casein, thus originating an unstable micelle state that results in clot formation....
. Tyrosine has a non-polar/hydrophobic side group (see table, amino acid
Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
). In fact, the word "tyrosine" is from the Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 tyros, meaning cheese
Cheese

Cheese is a food consisting of proteins and fat from milk, usually the milk of cattle, Water Buffalo, goats, or sheep's milk. It is produced by Coagulation of the milk protein casein....
, as it was first discovered in 1846 by German chemist Justus von Liebig
Justus von Liebig

Justus von Liebig was a German chemist who made major contributions to agriculture and biology chemistry, and worked on the organization of organic chemistry....
 in the protein casein from cheese.

Functions

Aside from being a proteogenic amino acid, tyrosine has a special role by virtue of the phenol
Phenol

Phenol, also known as carbolic acid, is a toxic, white crystalline solid with a sweet tarry odor, commonly referred to as a "hospital smell"....
 functionality. It occurs in proteins that are part of signal transduction
Signal transduction

In biology, 'signal transduction' refers to any process by which a cell converts one kind of signal or stimulus into another. Most processes of signal transduction involve ordered sequences of biochemistry chemical reaction inside the cell, which are carried out by enzymes, activated by Second messenger systems, resulting in a signal tran...
 processes. It functions as a receiver of phosphate groups that are transferred by way of protein kinase
Protein kinase

A protein kinase is a kinase enzyme that modifies other proteins by chemically adding phosphate groups to them . Phosphorylation usually results in a functional change of the target protein by changing enzyme catalysis, cellular location, or association with other proteins....
s (so-called receptor tyrosine kinase
Receptor tyrosine kinase

Receptor tyrosine kinases s are the high dissociation constant#Protein-Ligand binding cell surface receptors for many polypeptide growth factors, cytokines and hormones....
s). Phosphorylation of the hydroxyl group changes the activity of the target protein.

A tyrosine residue also plays an important role in photosynthesis
Photosynthesis

File:Seawifs global biosphere.jpgPhotosynthesis is a metabolic pathway that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight....
. In chloroplast
Chloroplast

Chloroplasts are organelles found in plant cells and other eukaryote organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve Thermodynamic free energy in the form of Adenosine triphosphate and reduce NADP to NADPH through a complex set of processes called photosynthesis....
s (photosystem II
Photosystem II

Photosystem II is the first protein complex in the Light-dependent reactions. It is located in the thylakoid membrane of plants, algae and cyanobacteria....
), it acts as an electron donor in the reduction
Reduction

Reduction, reduced, or reduce may refer to:...
 of oxidized chlorophyll
Chlorophyll

Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. Its name is derived from Greek language: ?????? and f????? ....
. In this process, it undergoes deprotonation
Deprotonation

Deprotonation is a chemistry term that refers to the removal of a proton from a molecule, forming the conjugate base. The relative ability for a molecule to give up a proton is measured by a pKa value....
 of its phenolic OH-group. This radical is subsequently reduced in the photosystem II by the four core manganese cluster.

Dietary Sources


Tyrosine, which can be synthesised in the body from phenylalanine
Phenylalanine

Phenylalanine is an a-amino acid with the chemical formula HO2CCHCH2C6H5, which is found naturally in the breast milk of mammals and manufactured for food and drink products and are also sold as nutritional supplements for their reputed analgesic and antidepressant effects....
, is also found in many high protein food products such as soy products, chicken, turkey, fish, peanuts, almonds, avocados, bananas, milk, cheese, yogurt, cottage cheese, lima beans, pumpkin seeds, and sesame seeds. Tyrosine can also be obtained through supplementation.

Biosynthesis


In plants and most microorganisms, tyr is produced via prephenate
Prephenic acid

Prephenic acid, more commonly known by its ion form prephenate, is an intermediate in the biosynthesis of the aromatic amino acids phenylalanine and tyrosine....
, an intermediate on the shikimate pathway
Shikimic acid

Shikimic acid, more commonly known as its ion form shikimate, is an important biochemical intermediate in plants and microorganisms. Its name comes from the Japanese flower shikimi , from which it was first isolated....
. Prephenate is oxidatively decarboxylated
Oxidative decarboxylation

Pyruvate decarboxylation is the biochemical reaction that uses pyruvate to form acetyl-CoA, releasing NADH, a reducing equivalent, and carbon dioxide....
 with retention of the hydroxyl
Hydroxyl

Hydroxyl in chemistry stands for a molecule consisting of an oxygen atom and a hydrogen atom connected by a covalent bond. The neutral form is a hydroxyl Radical and the hydroxyl anion is called a hydroxide....
 group to give p-hydroxyphenylpyruvate, which is transaminated
Transamination

There are two chemical reactions known as transamination . The first is the reaction between an amino acid and an alpha-keto acid. The amino group is transferred from the former to the latter; this results in the amino acid being converted to the corresponding a-keto acid, while the reactant a-keto acid is converted to the corresponding amin...
 using glutamate
Glutamic acid

Glutamic acid is one of the 20 proteinogenic amino acids and its codons are GAA and GAG. It is a non-essential amino acid. The carboxylate anions and salt of glutamic acid are known as glutamates....
 as the nitrogen source to give tyrosine and a-ketoglutarate
Ketoglutaric acid

a-Ketoglutaric acid is one of two ketone derivatives of glutaric acid. Its anion, a-ketoglutarate is an important biological compound. It is the keto acid produced by de-amination of glutamate, and is an intermediate in the Krebs cycle....
.

Mammals synthesize tyrosine from the essential amino acid phenylalanine
Phenylalanine

Phenylalanine is an a-amino acid with the chemical formula HO2CCHCH2C6H5, which is found naturally in the breast milk of mammals and manufactured for food and drink products and are also sold as nutritional supplements for their reputed analgesic and antidepressant effects....
 (phe), which is derived from food. The conversion of phe to tyr is catalyzed by the enzyme
Enzyme

Enzymes are biomolecules that catalysis chemical reactions. Almost all enzymes are proteins. In enzymatic reactions, the molecules at the beginning of the process are called Substrate , and the enzyme converts them into different molecules, the products....
 phenylalanine hydroxylase
Phenylalanine hydroxylase

Phenylalanine hydroxylase is an enzyme which catalyses the reaction causing the addition of an hydroxyl group to the end of the 6-carbon aromatic ring of phenylalanine, such that it becomes tyrosine:...
, a monooxygenase. This enzyme catalyzes the reaction causing the addition of an hydroxyl group to the end of the 6-carbon aromatic ring of phenylalanine, such that it becomes tyrosine.

Metabolism


Phosphorylation and sulphation

Some of the tyrosine residues can be tagged with a phosphate group (phosphorylated
Phosphorylation

Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Protein phosphorylation in particular plays a significant role in a wide range of cellular processes....
) by protein kinase
Protein kinase

A protein kinase is a kinase enzyme that modifies other proteins by chemically adding phosphate groups to them . Phosphorylation usually results in a functional change of the target protein by changing enzyme catalysis, cellular location, or association with other proteins....
s. (In its phosphorylated state, it is referred to as phosphotyrosine). Tyrosine phosphorylation is considered to be one of the key steps in signal transduction and regulation of enzymatic activity. Phosphotyrosine can be detected through specific antibodies
Antibody

Antibodies are gamma globulin proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacterium and viruses....
. Tyrosine residues may also be modified by the addition of a sulfate group, a process known as tyrosine sulfation
Tyrosine sulfation

Tyrosine sulfation is a posttranslational modification where a sulfate group is added to a tyrosine residue of a protein molecule. Secreted proteins and extracellular parts of membrane proteins that pass through the Golgi apparatus may be sulfated....
. Tyrosine sulfation
Tyrosine sulfation

Tyrosine sulfation is a posttranslational modification where a sulfate group is added to a tyrosine residue of a protein molecule. Secreted proteins and extracellular parts of membrane proteins that pass through the Golgi apparatus may be sulfated....
 is catalyzed by tyrosylprotein sulfotransferase (TPST). Like the phosphotyrosine antibodies mentioned above, antibodies have recently been described that specifically detect sulfotyrosine.

Precursor to hormones

In the adrenal gland
Adrenal gland

In mammals, the adrenal glands are the star-shaped endocrine glands that sit on top of the kidneys; their name indicates that position . They are chiefly responsible for regulating the stress response through the biosynthesis of corticosteroids and catecholamines, including cortisol and adrenaline, respectively....
, tyrosine is converted to levodopa
Levodopa

L-DOPA is a naturally occurring amino acid found in food and made from L-Tyrosine in the human body. L-DOPA is converted into dopamine in the brain and body....
 by the enzyme
Enzyme

Enzymes are biomolecules that catalysis chemical reactions. Almost all enzymes are proteins. In enzymatic reactions, the molecules at the beginning of the process are called Substrate , and the enzyme converts them into different molecules, the products....
 tyrosine hydroxylase
Tyrosine hydroxylase

Tyrosine hydroxylase or tyrosine 3-monooxygenase is the enzyme responsible for catalyzing the conversion of the amino acid L-tyrosine to dihydroxyphenylalanine ....
 (TH). TH is also the rate-limiting enzyme involved in the synthesis of the catecholamine
Catecholamine

Catecholamines are chemical compounds derived from the amino acid tyrosine. Their name is derived from the fact that they contain catechol and amine moieties....
 hormone
Hormone

Hormones are chemicals released by cells that affect cells in other parts of the body. Only a small amount of hormone is required to alter cell metabolism....
s dopamine
Dopamine

Dopamine is a neurotransmitter occurring in a wide variety of animals, including both vertebrates and invertebrates. In the human brain, this phenethylamine functions as a neurotransmitter, activating the five types of dopamine receptors ? D1, D2, D3, D4 and D5, and their variants....
, norepinephrine
Norepinephrine

Norepinephrine or noradrenaline is a catecholamine with dual roles as a hormone and a neurotransmitter.As a stress hormone, norepinephrine affects parts of the brain where attention and responding actions are controlled....
 (noradrenaline), and epinephrine
Epinephrine

Epinephrine is a hormone and neurotransmitter.Epinephrine increases the "fight or flight" response of the Sympathetic nervous system of the autonomic nervous system....
.

The thyroid
Thyroid

The thyroid is one of the largest endocrine glands in the body. This gland is found in the neck inferior to the thyroid cartilage and at approximately the same level as the cricoid cartilage....
 hormones triiodothyronine
Triiodothyronine

Triiodothyronine, carbonhydrogeniodinenitrogenoxygen, also known as T3, is a thyroid hormone.Thyroid-stimulating hormone activates the production of thyroxine and T3....
 (T3) and thyroxine
Thyroxine

Thyroxine, or 3,5,3',5'-tetra?iodothyronine , a form of thyroid hormones is the major hormone secreted by the follicular cells of the thyroid gland....
 (T4) in the colloid
Colloid

A colloid is a type of chemical mixture where one substance is dispersed evenly throughout another. The particles of the dispersed substance are only suspended in the mixture, unlike a solution, where they are completely dissolved within....
 of the thyroid
Thyroid

The thyroid is one of the largest endocrine glands in the body. This gland is found in the neck inferior to the thyroid cartilage and at approximately the same level as the cricoid cartilage....
 also are derived from tyrosine.

Precursor to alkaloids

In Papaver somniferum, the opium poppy, tyrosine is used to produce the alkaloid
Alkaloid

Alkaloids are naturally occurring chemical compounds containing base nitrogen atoms. The name derives from the word alkaline and was used to describe any nitrogen-containing base....
 morphine
Morphine

Morphine is a highly potent opiate analgesic Medication, is the principal active agent in opium, and is considered to be the prototypical opioid....
.

Precursor to pigments

Tyrosine is also the precursor to the pigment melanin
Melanin

Melanin is a class of compounds found in the plant, animal, and protista kingdom , where it serves predominantly as a pigment. The class of pigments are derivatives of the amino acid tyrosine....
.

Degradation


The decomposition of L-tyrosine (syn. para-hydroxyphenylalanine) begins with an a-ketoglutarate dependent transamination
Transamination

There are two chemical reactions known as transamination . The first is the reaction between an amino acid and an alpha-keto acid. The amino group is transferred from the former to the latter; this results in the amino acid being converted to the corresponding a-keto acid, while the reactant a-keto acid is converted to the corresponding amin...
 through the tyrosine transaminase to para-hydroxyphenylpyruvate. The positional description para, abbreviated p, mean that the hydroxyl group and side chain on the phenyl ring are across from each other (see the illustration below).

The next oxidation step catalyzes by p-hydroxylphenylpyruvate-dioxygenase and splitting off CO2 homogentisate (2,5-dihydroxyphenyl-1-acetate). In order to split the aromatic ring of homogentisate, a further dioxygenase, homogentistate-oxygenase is required. Thereby, through the incorporation of a further O2 molecule, maleylacetoacetate is created.

Fumarylacetate is created maleylacetoacetate-cis-trans-isomerase through rotation of the carboxyl group created from the hydroxyl group via oxidation. This cis-trans-isomerase contains glutathione
Glutathione

Glutathione is a tripeptide. It contains an unusual peptide linkage between the amino acid of cysteine and the carboxyl group of the glutamate side chain....
 as a coenzyme
Coenzyme

Many enzymes require a cofactor for catalytic activity, accelerating the transformation of a specific substrate to a particular product. The inactive protein, without the cofactor is called an apoenzyme, while the complete enzyme with cofactor is the holoenzyme....
. Fumarylacetoacetate is finally split via fumarylacetoacetate-hydrolase through the addition of a water molecule.

Thereby fumarate (also a metabolite of the citric acid cycle) and acetoacetate
Acetoacetic acid

Acetoacetic acid is the organic compound with the formula CH3CCH2CO2H....
 (3-ketobutyroate) are liberated. Acetoacetate is a ketone body, which is activated with succinyl-CoA, and thereafter it can be converted into acetyl-CoA
Acetyl-CoA

Acetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main use is to convey the carbon atoms within the acetyl group to the citric acid cycle to be oxidation for energy production....
 which in turn can be oxidized by the citric acid cycle
Citric acid cycle

The citric acid cycle ? also known as the tricarboxylic acid cycle ; the Krebs cycle; or, more rarely, the Szent-Gy?rgyi-Krebs cycle) ? is a series of enzyme-catalysed chemical reactions of central importance in all living cell s that use oxygen as part of cellular respiration....
 or be used for fatty acid synthesis
Fatty acid synthesis

Fatty acids are formed by the action of fatty acid synthase from acetyl-CoA and malonyl-CoA precursors....
.

Ortho- and meta-tyrosine


Three isomer
Isomer

In chemistry, isomers are compounds with the same molecular formula but different structural formulae. Isomers do not necessarily share similar properties unless they also have the same functional groups....
s of tyrosine are known. In addition to common amino acid L-tyrosine which is the para isomer (para-tyr, p-tyr or 4-hydroxyphenylalanine) there are two additional regioisomers, namely meta-tyrosine (m-tyr or 3-hydroxyphenylalanine or L-m-tyrosine) and ortho-tyrosine (o-tyr or 2-hydroxyphenylalanine) which occur in nature. The m-tyr and o-tyr isomers, which are rare, arise through non-enzymatic free-radical hydroxylation of phenylalanine under conditions of oxidative stress
Oxidative stress

Oxidative stress is caused by an imbalance between the production of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or easily repair the resulting damage....
.

m-Tyrosine and analogues (rare in nature and therefore available synthetically) have shown application in Parkinson's Disease
Parkinson's disease

Parkinson's disease is a degenerative disorder of the central nervous system that often impairs the sufferer's motor skills and speech, as well as other functions....
, Alzheimer's disease
Alzheimer's disease

Alzheimer's disease , also called Alzheimer disease, Senile Dementia of the Alzheimer Type or simply Alzheimer's, is the most common form of dementia....
 and arthritis
Arthritis

Arthritis is a group of conditions involving damage to the joints of the body. Arthritis is the leading cause of disability in people older than fifty-five years....
 .

Medical use


Tyrosine is a precursor to neurotransmitter
Neurotransmitter

Neurotransmitters are chemistry which relay, amplify and modulate signals between a neuron and another cell . Neurotransmitters are packaged into vesicles that cluster beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to receptors in the membrane on the postsynaptic side of...
s and increases plasma neurotransmitter levels (particularly dopamine and norepinephrine) but has little if any effect on mood. The effect on mood is more noticeable in humans subjected to stressful conditions (see below).

A number of studies have found tyrosine to be useful during conditions of stress, cold, fatigue, prolonged work and sleep deprivation, with reductions in stress hormone levels, reductions in stress-induced weight loss seen in animal trials, improvements in cognitive and physical performance seen in human trials. Because tyrosine hydroxylase is the rate limiting enzyme, however, effects are less significant than those of l-dopa.

Tyrosine does not seem to have any significant effect on mood, cognitive or physical performance in normal circumstances. A daily dosage supported in the literature is about 100 mg/kg for an adult. The usual dosage amounts to 500-1500 mg per day (dose suggested by most manufacturers; usually an equivalent to 1-3 capsules of pure tyrosine). It is not recommended to exceed 12000 mg (12 g) per day. In fact, too high doses result in reduced levels of dopamine. Tyrosine may decrease the absorption of other amino acids in high or chronic doses. It decreases absorption of l-dopa.

Drug Detoxification

Tyrosine appears to be a successful addition to conventional treatment for cocaine abuse and withdrawal. It may be used in conjunction with other amino acids such as tryptophan
Tryptophan

Tryptophan is one of the 20 List of standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG....
. Some individuals using tyrosine have also reported successful withdrawal from caffeine and nicotine.

See also

  • Tyramine
    Tyramine

    In organic chemistry chemistry tyramine is a monoamine Chemical compound derived from the amino acid tyrosine. Tyramine can cause the release of stored monoamines, such as dopamine, norepinephrine, and epinephrine....
  • Alkaptonuria
    Alkaptonuria

    Alkaptonuria is a rare inherited genetic disorder of phenylalanine and tyrosine metabolism. This is an autosomal dominance relationship that is due to a defect in the enzyme homogentisate 1,2-dioxygenase , which participates in Tyrosine#Degradation tyrosine....
  • Tyrosinemia
    Tyrosinemia

    Tyrosinemia is an error of metabolism, usually inborn, in which the body cannot effectively break down the amino acid tyrosine. Symptoms include liver and kidney disturbances and mental retardation....
  • Albinism
    Albinism

    Albinism is a form of hypopigmentation congenital disorder, characterized by a partial or total lack of melanin Biological pigment in the eyes, skin and hair ....
  • Causes of Autism
    Causes of autism

    Autism and autism spectrum disorders are complex neurodevelopmental disorders. Many causes of autism have been proposed, but its Etiology is still incomplete....
     (Section Thyroid problems)
  • Tyrosine sulfation
    Tyrosine sulfation

    Tyrosine sulfation is a posttranslational modification where a sulfate group is added to a tyrosine residue of a protein molecule. Secreted proteins and extracellular parts of membrane proteins that pass through the Golgi apparatus may be sulfated....
  • Betalain
    Betalain

    Betalains are a class of red and yellow indole-derived Biological pigment found in plants of the Caryophyllales. They are most often noticeable in the petals of flowers, but may color the fruits, leaf, plant stem, and roots of plants that contain them....
Iodinated tyrosine derivatives

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