Pathways

Tyrosine is one of the amino acid used in protein synthesis. The tyrosine biosynthesis pathways is connected with the chorismate biosynthesis pathway. Chorismate biosynthesis produce the chorismate, which can further be converted to prephenate by T-protein. Combined with cofactor, NAD, prephenate has been further converted to 4-Hydroxyphenylpyruvic acid by T-protein with generated NADH and carbon dioxide. Tyrosine aminotransferase catalyzes 4-Hydroxyphenylpyruvic acid to tyrosine, and also converts glutamic acid to oxoglutaric acid. Tyrosine will be further catalyzed into various molecules such as 2-iminoacetate, p-Cresol, 5'Deoxyadenosine and L-Methionine; or it will be exported from cell via the lysine exporter.

Tyrosine is one of the amino acid used in protein synthesis. The tyrosine biosynthesis pathways is connected with the chorismate biosynthesis pathway. Chorismate biosynthesis produce the chorismate, which can further be converted to prephenate by T-protein. Combined with cofactor, NAD, prephenate has been further converted to 4-Hydroxyphenylpyruvic acid by T-protein with generated NADH and carbon dioxide. Tyrosine aminotransferase catalyzes 4-Hydroxyphenylpyruvic acid to tyrosine, and also converts glutamic acid to oxoglutaric acid. Tyrosine will be further catalyzed into various molecules such as 2-iminoacetate, p-Cresol, 5'Deoxyadenosine and L-Methionine; or it will be exported from cell via the lysine exporter.

Tyrosine is one of the amino acid used in protein synthesis. The tyrosine biosynthesis pathways is connected with the chorismate biosynthesis pathway. Chorismate biosynthesis produce the chorismate, which can further be converted to prephenate by T-protein. Combined with cofactor, NAD, prephenate has been further converted to 4-Hydroxyphenylpyruvic acid by T-protein with generated NADH and carbon dioxide. Tyrosine aminotransferase catalyzes 4-Hydroxyphenylpyruvic acid to tyrosine, and also converts glutamic acid to oxoglutaric acid. Tyrosine will be further catalyzed into various molecules such as 2-iminoacetate, p-Cresol, 5'Deoxyadenosine and L-Methionine; or it will be exported from cell via the lysine exporter.

Tyrosine is one of the amino acid used in protein synthesis. The tyrosine biosynthesis pathways is connected with the chorismate biosynthesis pathway. Chorismate biosynthesis produce the chorismate, which can further be converted to prephenate by T-protein. Combined with cofactor, NAD, prephenate has been further converted to 4-Hydroxyphenylpyruvic acid by T-protein with generated NADH and carbon dioxide. Tyrosine aminotransferase catalyzes 4-Hydroxyphenylpyruvic acid to tyrosine, and also converts glutamic acid to oxoglutaric acid. Tyrosine will be further catalyzed into various molecules such as 2-iminoacetate, p-Cresol, 5'Deoxyadenosine and L-Methionine; or it will be exported from cell via the lysine exporter.

Tyrosine Hydroxylase (TH) Deficiency is a rare inborn error of metabolism (IEM) and autosomal recessive disorder of catecholamines pathways. The disorder is caused by defects in the Tyrosine hydroxylase (TH) gene which encodes for the enzyme tyrosine hydroxylase. This enzyme is part of the production of catecholamines such as dopamine, norepinephrine and epinephrine are all essential for normal nervous system function. Dopamine transmits signals to help the brain control physical movement and emotional behavior. Norepinephrine and epinephrine are involved in the autonomic nervous system. Mutations in the TH gene result in reduced activity of the tyrosine hydroxylase enzyme. As a result, the body produces less dopamine, norepinephrine and epinephrine. Symptoms of the disorder include abnormal movements, autonomic dysfunction, and other neurological problems. Treatments can include the administration of levodopa; however patient responses can vary greatly. The frequency of Tyrosine Hydroxylase Deficiency is unknown.

Tyrosine Hydroxylase (TH) Deficiency is a rare inborn error of metabolism (IEM) and autosomal recessive disorder of catecholamines pathways. The disorder is caused by defects in the Tyrosine hydroxylase (TH) gene which encodes for the enzyme tyrosine hydroxylase. This enzyme is part of the production of catecholamines such as dopamine, norepinephrine and epinephrine are all essential for normal nervous system function. Dopamine transmits signals to help the brain control physical movement and emotional behavior. Norepinephrine and epinephrine are involved in the autonomic nervous system. Mutations in the TH gene result in reduced activity of the tyrosine hydroxylase enzyme. As a result, the body produces less dopamine, norepinephrine and epinephrine. Symptoms of the disorder include abnormal movements, autonomic dysfunction, and other neurological problems. Treatments can include the administration of levodopa; however patient responses can vary greatly. The frequency of Tyrosine Hydroxylase Deficiency is unknown.

Tyrosine Hydroxylase (TH) Deficiency is a rare inborn error of metabolism (IEM) and autosomal recessive disorder of catecholamines pathways. The disorder is caused by defects in the Tyrosine hydroxylase (TH) gene which encodes for the enzyme tyrosine hydroxylase. This enzyme is part of the production of catecholamines such as dopamine, norepinephrine and epinephrine are all essential for normal nervous system function. Dopamine transmits signals to help the brain control physical movement and emotional behavior. Norepinephrine and epinephrine are involved in the autonomic nervous system. Mutations in the TH gene result in reduced activity of the tyrosine hydroxylase enzyme. As a result, the body produces less dopamine, norepinephrine and epinephrine. Symptoms of the disorder include abnormal movements, autonomic dysfunction, and other neurological problems. Treatments can include the administration of levodopa; however patient responses can vary greatly. The frequency of Tyrosine Hydroxylase Deficiency is unknown.

The tyrosine metabolism pathway describes the many ways in which tyrosine is catabolized or transformed to generate a wide variety of biologically important molecules. In particular, tyrosine can be metabolized to produce hormones such as thyroxine and triiodothyronine or it can be metabolized to produce neurotransmitters such as L-DOPA, dopamine, adrenaline, or noradrenaline. Tyrosine can also serve as a precursor of the pigment melanin and for the formation of Coenzyme Q10. Additionally, tyrosine can be catabolized all the way down into fumarate and acetoacetate. This particular pathway for tyrosine degradation starts with an alpha-ketoglutarate-dependent transamination reaction of tyrosine, which is mediated through the enzyme known as tyrosine transaminase. This process generates p-hydroxyphenylpyruvate. This aromatic acid is then acted upon by p-hydroxylphenylpyruvate-dioxygenase which generates the compound known as homogentisic acid or homogentisate (2,5-dihydroxyphenyl-1-acetate). In order to split the aromatic ring of homogentisate, a unique dioxygenase enzyme known as homogentisic acid 1,2-dioxygenase is required. Through this enzyme, maleylacetoacetate is created from the homogentisic acid precursor. The accumulation of excess homogentisic acid and its oxide (named alkapton) in the urine of afflicted individuals can lead to a condition known as alkaptonuria. This genetic condition, also known as an inborn error of metabolism or IEM, occurs if there are mutations in the homogentisic acid 1,2-dioxygenase gene. After the breakdown of homogentisate is achieved, maleylacetoacetate is then attacked by the enzyme known as maleylacetoacetate-cis-trans-isomerase, which generates fumarylacetate. This isomerase catalyzes the rotation of the carboxyl group created from the hydroxyl group via oxidation. This cis-trans-isomerase uses glutathione as a coenzyme or cofactor. The resulting product, fumarylacetoacetate, is then split into acetoactate and fumarate via the enzyme known as fumarylacetoacetate-hydrolase through the addition of a water molecule. Through this set of reactions fumarate and acetoacetate (3-ketobutyroate) are liberated. Acetoacetate is a ketone body, which is activated with succinyl-CoA, and thereafter it can be converted into acetyl-CoA, which in turn can be oxidized by the citric acid cycle (also known as the TCA cycle) or used for fatty acid synthesis. Other aspects of tyrosine metabolism include the generation of catecholamines. In this process, the enzyme known as tyrosine hydroxylase (or AAAH or TYH) catalyzes the conversion of tyrosine to L-DOPA. The L-DOPA can then be converted via the enzyme DOPA decarboxylase (DDC) to dopamine. Dopamine can then be converted to 3-methoxytyramine via the action of catechol-O-methyltransferase (COMT). Dopamine can also be converted to norepinephrine (noradrenaline) through the action of the enzyme known as dopamine beta hydroxylase (DBH). Norepinephrine can then be converted to epinephrine (adrenaline) through the action of phenyethanolamine N-methyltransferase (PNMT). Catecholamines such as L-DOPA, dopamine and methoxytyramine are produced mainly by the chromaffin cells of the adrenal medulla and by neuronal cells found in the brain. For example, dopamine, which acts as a neurotransmitter, is mostly produced in neuronal cell bodies in the ventral tegmental area and the substantia nigra while epinephrine is produced in neurons in the human brain that express PMNT. Catecholamines typically have a half-life of a few minutes in the blood. They are typically degraded via catechol-O-methyltransferases (COMT) or by deamination via monoamine oxidases (MAO). Another important aspect of tyrosine metabolism includes the production of melanin. Melanin is produced through a mechanism known as melanogenesis, a process that involves the oxidation of tyrosine followed by the polymerization of these oxidation by-products. Melanin pigments are produced in a specialized group of cells known as melanocytes. There are three types of melanin: pheomelanin, eumelanin, and neuromelanin of which eumelanin is the most common. Melanogenesis, especially in the skin, is initiated through the exposure to UV light. Melanin is the primary pigment that determines skin color. Melanin is also found in hair and the pigmented tissue underlying the iris. The first step in the synthesis for both eumelanins and pheomelanins is the conversion of tyrosine to dopaquinone by the enzyme known as tyrosinase. The resulting dopaquinone can combine with cysteine to produce cysteinyldopa, which then polymerizes to form pheomelanin. Dopaquinone can also form lecuodopachrome, which then can be converted to dopachrome (a cyclization product) and this eventually becomes eumelanin. Tyrosine plays a critical role in the synthesis of thyroid hormones. Thyroid hormones are produced and released by the thyroid gland and include triiodothyronine (T3) and thyroxine (T4). These two hormones are responsible for regulating metabolism. Thyroxine was discovered and isolated by Edward Calvin Kendall in 1915. Thyroid hormones are produced by the follicular cells of the thyroid gland through the action of thyroperoxidase, which iodinates reactive tyrosine residues on thyroglobulin. Proteolysis of the thyroglobulin in cellular lysosomes releases the small molecule thyroid hormones. In mammals, tyrosine can be formed from dietary phenylalanine by the enzyme phenylalanine hydroxylase, found in large amounts in the liver. Phenylalanine is considered an essential amino acid, while tyrosine (which can be endogenously synthesized) is not. In plants and most microbes, tyrosine is produced via prephenate, an intermediate that is produced as part of the shikimate pathway.

The biosynthesis of tyrosine begins with chorismate interacting with chorismate mutase resulting in a prephenate. Prephenate reacts with a hydrogen ion through a prephenate dehydratase resulting in the release of NADPH, carbon dioxide and 4-hydroxyphenylpyruvate. The latter compound can be turn into tyrosine through two different reversible reactions a) 4-hydroxyphenylpyruvate reacts with alanine through a aromatic amino acid aminotransferase 2 resulting in the release of pyruvate and phenylalanine. b) 4-hydroxyphenylpyruvatereacts with glutamic acid through a amino aci aminotransferase 1 resulting in the release of oxoglutaric acid and phenylalanine. The degradation of phenylalanine begins with the two previous reactions turning phenylalanine back into 4-hydroxyphenylpyruvate. The latter compound reacts with a phenylpyruvate carboxy lyase resulting in the release of phenylacetaldehyde. This latter compound reacts with a alcohol dehydrogenase resulting in the release of tyrosol.