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35-468: L -Tyrosine or tyrosine (symbol Tyr or Y ) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins . It is a conditionally essential amino acid with a polar side group . The word "tyrosine" is from the Greek tyrós , meaning cheese , as it was first discovered in 1846 by German chemist Justus von Liebig in the protein casein from cheese. It

70-917: A nucleotide sequence known as a SECIS element , which directs the cell to translate a nearby UGA codon as selenocysteine (UGA is normally a stop codon ). In some methanogenic prokaryotes, the UAG codon (normally a stop codon) can also be translated to pyrrolysine . In eukaryotes, there are only 21 proteinogenic amino acids, the 20 of the standard genetic code, plus selenocysteine . Humans can synthesize 12 of these from each other or from other molecules of intermediary metabolism. The other nine must be consumed (usually as their protein derivatives), and so they are called essential amino acids . The essential amino acids are histidine , isoleucine , leucine , lysine , methionine , phenylalanine , threonine , tryptophan , and valine (i.e. H, I, L, K, M, F, T, W, V). The proteinogenic amino acids have been found to be related to

105-614: A urinary metabolite of tyrosine in rats. Three structural isomers of L-tyrosine are known. In addition to the 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 (also known as 3-hydroxyphenylalanine , L- m -tyrosine , and m -tyr) and ortho -tyrosine ( o -tyr or 2-hydroxyphenylalanine), that 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 . Tyrosine

140-408: Is transaminated using glutamate as the nitrogen source to give tyrosine and α-ketoglutarate . Mammals synthesize tyrosine from the essential amino acid phenylalanine (Phe), which is derived from food. The conversion of Phe to Tyr is catalyzed by the enzyme phenylalanine hydroxylase , a monooxygenase. This enzyme catalyzes the reaction causing the addition of a hydroxyl group to the end of

175-472: Is a precursor of phenylalanine. Alternatively, it can be dehydrated by prephenate dehydrogenase to 4-hydroxyphenylpyruvic acid , which is a precursor of tyrosine. It is biosynthesized by a [3,3]- sigmatropic Claisen rearrangement of chorismate . Prephenic acid is unstable; as a 1,4-cyclohexadiene , it is easily aromatized , for example, under the influence of acids or bases. This instability makes both isolation and synthesis difficult. Prephenic acid

210-530: Is a precursor to neurotransmitters and increases plasma neurotransmitter levels (particularly dopamine and norepinephrine), but has little if any effect on mood in normal subjects. A 2015 systematic review found that "tyrosine loading acutely counteracts decrements in working memory and information processing that are induced by demanding situational conditions such as extreme weather or cognitive load " and therefore "tyrosine may benefit healthy individuals exposed to demanding situational conditions". L-tyrosine

245-471: Is an intermediate in the biosynthesis of the aromatic amino acids phenylalanine and tyrosine , as well as of a large number of secondary metabolites of the shikimate pathway . Prephenic acid occurs naturally as an intermediate in the biosynthesis of phenylalanine and tyrosine via the shikimic acid pathway . It is formed from chorismic acid by chorismate mutase . It can be dehydrated by prephenate dehydratase to phenylpyruvic acid , which

280-413: Is based on 135 Archaea, 3775 Bacteria, 614 Eukaryota proteomes and human proteome (21 006 proteins) respectively. In mass spectrometry of peptides and proteins, knowledge of the masses of the residues is useful. The mass of the peptide or protein is the sum of the residue masses plus the mass of water ( Monoisotopic mass = 18.01056 Da; average mass = 18.0153 Da). The residue masses are calculated from

315-432: Is called tyrosyl when referred to as a functional group or side chain. While tyrosine is generally classified as a hydrophobic amino acid, it is more hydrophilic than phenylalanine . It is encoded by the codons UAC and UAU in messenger RNA . The one-letter symbol Y was assigned to tyrosine for being alphabetically nearest of those letters available. Note that T was assigned to the structurally simpler threonine, U

350-416: Is included for completeness. †† UAG and UGA do not always act as stop codons (see above). ‡ An essential amino acid cannot be synthesized in humans and must, therefore, be supplied in the diet. Conditionally essential amino acids are not normally required in the diet, but must be supplied exogenously to specific populations that do not synthesize it in adequate amounts. & Occurrence of amino acids

385-409: Is one of the post-translational modifications . Phosphorylated tyrosine occurs in proteins that are part of signal transduction processes. Similar functionality is also presented in serine and threonine , whose side chains have a hydroxy group, but are alcohols . Phosphorylation of these three amino acids' moieties (including tyrosine) creates a negative charge on their ends, that is greater than

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420-414: Is the rate-limiting enzyme involved in the synthesis of the neurotransmitter dopamine . Dopamine can then be converted into other catecholamines , such as norepinephrine (noradrenaline) and epinephrine (adrenaline). The thyroid hormones triiodothyronine (T 3 ) and thyroxine (T 4 ) in the colloid of the thyroid are also derived from tyrosine. The latex of Papaver somniferum ,

455-405: Is used in pharmaceuticals , dietary supplements , and food additives . Two methods were formerly used to manufacture L-tyrosine. The first involves the extraction of the desired amino acid from protein hydrolysates using a chemical approach. The second utilizes enzymatic synthesis from phenolics, pyruvate, and ammonia through the use of tyrosine phenol-lyase . Advances in genetic engineering and

490-513: The 6-carbon aromatic ring of phenylalanine , such that it becomes tyrosine. Some of the tyrosine residues can be tagged (at the hydroxyl group) with a phosphate group ( phosphorylated ) by protein kinases . In its phosphorylated form, tyrosine is called 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 . Tyrosine residues may also be modified by

525-419: The activity of the target protein, or may form part of a signaling cascade via SH2 domain binding. A tyrosine residue also plays an important role in photosynthesis . In chloroplasts ( photosystem II ), it acts as an electron donor in the reduction of oxidized chlorophyll . In this process, it loses the hydrogen atom of its phenolic OH-group. This radical is subsequently reduced in the photosystem II by

560-409: The addition of a sulfate group, a process known as tyrosine sulfation . Tyrosine sulfation is catalyzed by tyrosylprotein sulfotransferase (TPST). Like the phosphotyrosine antibodies mentioned above, antibodies have recently been described that specifically detect sulfotyrosine. In dopaminergic cells in the brain , tyrosine is converted to L-DOPA by the enzyme tyrosine hydroxylase (TH). TH

595-400: The addition of a water molecule. Thereby fumarate (also a metabolite of the citric acid cycle) 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 or be used for fatty acid synthesis . Phloretic acid is also

630-797: The advent of industrial fermentation have shifted the synthesis of L-tyrosine to the use of engineered strains of E. coli . Proteinogenic amino acid In contrast, non-proteinogenic amino acids are amino acids that are either not incorporated into proteins (like GABA , L -DOPA , or triiodothyronine ), misincorporated in place of a genetically encoded amino acid, or not produced directly and in isolation by standard cellular machinery (like hydroxyproline ). The latter often results from post-translational modification of proteins. Some non-proteinogenic amino acids are incorporated into nonribosomal peptides which are synthesized by non-ribosomal peptide synthetases. Both eukaryotes and prokaryotes can incorporate selenocysteine into their proteins via

665-414: The amino acid residue placed centrally in an alanine pentapeptide. The value for Arg is from Pace et al. (2009). The value for Sec is from Byun & Kang (2011). N.D.: The pKa value of Pyrrolysine has not been reported. Note: The pKa value of an amino-acid residue in a small peptide is typically slightly different when it is inside a protein. Protein pKa calculations are sometimes used to calculate

700-423: The change in the pKa value of an amino-acid residue in this situation. * UAG is normally the amber stop codon , but in organisms containing the biological machinery encoded by the pylTSBCD cluster of genes the amino acid pyrrolysine will be incorporated. ** UGA is normally the opal (or umber) stop codon, but encodes selenocysteine if a SECIS element is present. † The stop codon is not an amino acid, but

735-607: The four core manganese clusters . The Dietary Reference Intake for tyrosine is usually estimated together with phenylalanine . It varies depending on an estimate method, however the ideal proportion of these two amino acids is considered to be 60:40 (phenylalanine:tyrosine) as a human body has such composition. Tyrosine, which can also be synthesized in the body from phenylalanine, is found in many high- protein food products such as meat , fish , cheese , cottage cheese , milk , yogurt , peanuts , almonds , pumpkin seeds , sesame seeds , soy protein and lima beans . For example,

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770-404: 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 -hydroxyphenylpyruvate dioxygenase and splitting off CO 2 homogentisate (2,5-dihydroxyphenyl-1-acetate). In order to split the aromatic ring of homogentisate, a further dioxygenase, homogentisate 1,2-dioxygenase is required. Thereby, through

805-409: The incorporation of a further O 2 molecule, maleylacetoacetate is created. Fumarylacetoacetate is created by maleylacetoacetate cis - trans -isomerase through rotation of the carboxyl group created from the hydroxyl group via oxidation. This cis-trans -isomerase contains glutathione as a coenzyme . Fumarylacetoacetate is finally split by the enzyme fumarylacetoacetate hydrolase through

840-454: The metabolic cost (ATP) for synthesis of the amino acids. Negative numbers indicate the metabolic processes are energy favorable and do not cost net ATP of the cell. The abundance of amino acids includes amino acids in free form and in polymerization form (proteins). Amino acids can be classified according to the properties of their main products: Prephenic acid Prephenic acid , commonly also known by its anionic form prephenate ,

875-406: The negative charge of the only negatively charged aspartic and glutamic acids. Phosphorylated proteins keep these same properties—which are useful for more reliable protein-protein interactions—by means of phosphotyrosine, phosphoserine and phosphothreonine. Binding sites for a signalling phosphoprotein may be diverse in their chemical structure. Phosphorylation of the hydroxyl group can change

910-411: The opium poppy, has been shown to convert tyrosine into the alkaloid morphine and the bio-synthetic pathway has been established from tyrosine to morphine by using Carbon-14 radio-labelled tyrosine to trace the in-vivo synthetic route. Tyrosine ammonia lyase (TAL) is an enzyme in the natural phenols biosynthesis pathway. It transforms L-tyrosine into p-coumaric acid . Tyrosine is also the precursor to

945-462: The peptide backbone and fragment the protein with relatively short half-lives , while others are toxic because they can be mistakenly incorporated into proteins, such as the arginine analog canavanine . The evolutionary selection of certain proteinogenic amino acids from the primordial soup has been suggested to be because of their better incorporation into a polypeptide chain as opposed to non-proteinogenic amino acids. The following illustrates

980-417: The pigment melanin . Tyrosine (or its precursor phenylalanine) is needed to synthesize the benzoquinone structure which forms part of coenzyme Q10 . The decomposition of L-tyrosine (syn. para -hydroxyphenylalanine) begins with an α-ketoglutarate dependent transamination through the tyrosine transaminase to para -hydroxyphenylpyruvate . The positional description para , abbreviated p , mean that

1015-420: The set of amino acids that can be recognized by ribozyme autoaminoacylation systems. Thus, non-proteinogenic amino acids would have been excluded by the contingent evolutionary success of nucleotide-based life forms. Other reasons have been offered to explain why certain specific non-proteinogenic amino acids are not generally incorporated into proteins; for example, ornithine and homoserine cyclize against

1050-418: The structures and abbreviations of the 21 amino acids that are directly encoded for protein synthesis by the genetic code of eukaryotes. The structures given below are standard chemical structures, not the typical zwitterion forms that exist in aqueous solutions. IUPAC / IUBMB now also recommends standard abbreviations for the following two amino acids: Following is a table listing the one-letter symbols,

1085-445: The tabulated chemical formulas and atomic weights. In mass spectrometry , ions may also include one or more protons ( Monoisotopic mass = 1.00728 Da; average mass* = 1.0074 Da). *Protons cannot have an average mass, this confusingly infers to Deuterons as a valid isotope, but they should be a different species (see Hydron (chemistry) ) § Monoisotopic mass The table below lists the abundance of amino acids in E.coli cells and

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1120-484: The three-letter symbols, and the chemical properties of the side chains of the standard amino acids. The masses listed are based on weighted averages of the elemental isotopes at their natural abundances . Forming a peptide bond results in elimination of a molecule of water . Therefore, the protein's mass is equal to the mass of amino acids the protein is composed of minus 18.01524 Da per peptide bond. §: Values for Asp, Cys, Glu, His, Lys & Tyr were determined using

1155-417: The white of an egg has about 250 mg per egg, while beef, lamb, pork, tuna, salmon, chicken, and turkey contain about 500–1000 mg per 3 ounces (85 g) portion. In plants and most microorganisms, tyrosine is produced via prephenate , an intermediate on the shikimate pathway . Prephenate is oxidatively decarboxylated with retention of the hydroxyl group to give p -hydroxyphenylpyruvate, which

1190-476: Was avoided for its similarity with V for valine, W was assigned to tryptophan, while X was reserved for undetermined or atypical amino acids. The mnemonic t Y rosine was also proposed. Aside from being a proteinogenic amino acid , tyrosine has a special role by virtue of the phenol functionality. Its hydroxy group is able to form the ester linkage , with phosphate in particular. Phosphate groups are transferred to tyrosine residues by way of protein kinases . This

1225-505: Was first isolated from mutants of Escherichia coli that were unable to convert prephenic acid to phenylpyruvic acid . During this process, the barium salt was obtained. Prephenic acid is an example of achiral (optically inactive) molecule which has two pseudoasymmetric atoms ( i.e. stereogenic but not chirotopic centers), the C1 and the C4 cyclohexadiene ring atoms. It has been shown that of

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