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 was avoided for its similarity with V for valine, W was assigned to tryptophan, while X was reserved for undetermined or atypical amino acids.[6] The mnemonic tYrosine was also proposed.[7]
Similar functionality is also presented inserine andthreonine, whose side chains have a hydroxy group, but arealcohols. Phosphorylation of these three amino acids' moieties (including tyrosine) creates a negative charge on their ends, that is greater than the negative charge of the only negatively chargedaspartic andglutamic acids. Phosphorylated proteins keep these same properties—which are useful for more reliable protein-protein interactions—by means of phosphotyrosine, phosphoserine and phosphothreonine.[8]
Binding sites for a signalling phosphoprotein may be diverse in their chemical structure.[9]
Phosphorylation of the hydroxyl group can change the activity of the target protein, or may form part of a signaling cascade viaSH2 domain binding.[10]
A tyrosine residue also plays an important role inphotosynthesis. Inchloroplasts (photosystem II), it acts as an electron donor in thereduction of oxidizedchlorophyll. In this process, it loses the hydrogen atom of its phenolic OH-group. This radical is subsequently reduced in the photosystem II by the four coremanganese clusters.[11]
TheDietary Reference Intake for tyrosine is usually estimated together withphenylalanine. 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.[12]Tyrosine, which can also be synthesized in the body from phenylalanine, is found in many high-protein food products such asmeat,fish,cheese,cottage cheese,milk,yogurt,peanuts,almonds,pumpkin seeds,sesame seeds,soy protein andlima beans.[13][14] For example, the white of an egg has about 250 mg per egg,[15] while beef, lamb, pork, tuna, salmon, chicken, and turkey contain about 500–1000 mg per 3 ounces (85 g) portion.[15][16]
Mammals synthesize tyrosine from the essential amino acidphenylalanine (Phe), which is derived from food. The conversion of Phe to Tyr is catalyzed by theenzymephenylalanine hydroxylase, a monooxygenase. This enzyme catalyzes the reaction causing the addition of a hydroxyl group to the end of the 6-carbon aromatic ring ofphenylalanine, such that it becomes tyrosine.
Some of the tyrosine residues can betagged (at the hydroxyl group) with a phosphate group (phosphorylated) byprotein kinases. In its phosphorylated form, tyrosine is calledphosphotyrosine. Tyrosine phosphorylation is considered to be one of the key steps in signal transduction and regulation of enzymatic activity. Phosphotyrosine can be detected through specificantibodies. Tyrosine residues may also be modified by the addition of a sulfate group, a process known astyrosine sulfation.[17]Tyrosine sulfation is catalyzed bytyrosylprotein sulfotransferase (TPST). Like the phosphotyrosine antibodies mentioned above, antibodies have recently been described that specifically detect sulfotyrosine.[18]
The latex ofPapaver somniferum, the opium poppy, has been shown to convert tyrosine into thealkaloidmorphine 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.[22]Tyrosine ammonia lyase (TAL) is an enzyme in the natural phenols biosynthesis pathway. It transformsL-tyrosine intop-coumaric acid. Tyrosine is also the precursor to the pigmentmelanin. Tyrosine (or its precursor phenylalanine) is needed to synthesize the benzoquinone structure which forms part ofcoenzyme Q10.[23][24]
The decomposition of tyrosine toacetoacetate andfumarate. Two dioxygenases are necessary for the decomposition path. The end products can then enter into thecitric acid cycle.
The decomposition ofL-tyrosine (syn.para-hydroxyphenylalanine) begins with an α-ketoglutarate dependenttransamination through thetyrosine transaminase topara-hydroxyphenylpyruvate. The positional descriptionpara, abbreviatedp, mean that the hydroxyl group and side chain on the phenyl ring are across from each other (see the illustration below).
Therebyfumarate (also a metabolite of the citric acid cycle) andacetoacetate (3-ketobutyroate) are liberated. Acetoacetate is aketone body, which is activated with succinyl-CoA, and thereafter it can be converted intoacetyl-CoA, which in turn can be oxidized by thecitric acid cycle or be used forfatty acid synthesis.
Threestructural isomers ofL-tyrosine are known. In addition to the common amino acidL-tyrosine, which is thepara isomer (para-tyr,p-tyr or 4-hydroxyphenylalanine), there are two additional regioisomers, namelymeta-tyrosine (also known as3-hydroxyphenylalanine,L-m-tyrosine, andm-tyr) andortho-tyrosine (o-tyr or 2-hydroxyphenylalanine), that occur in nature. Them-tyr ando-tyr isomers, which are rare, arise through non-enzymaticfree-radical hydroxylation of phenylalanine under conditions ofoxidative stress.[27][28]
Tyrosine is a precursor toneurotransmitters and increases plasma neurotransmitter levels (particularly dopamine and norepinephrine),[29] but has little if any effect on mood in normal subjects.[30][31][32]
A 2015systematic 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 orcognitive load" and therefore "tyrosine may benefit healthy individuals exposed to demanding situational conditions".[33]
L-Tyrosine is used inpharmaceuticals,dietary supplements, andfood additives. Two methods were formerly used to manufactureL-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 oftyrosine phenol-lyase.[34] Advances ingenetic engineering and the advent ofindustrial fermentation have shifted the synthesis of L-tyrosine to the use of engineered strains ofE. coli.[35][34]
^abFrey MN, Koetzle TF, Lehmann MS, Hamilton WC (1973). "Precision neutron diffraction structure determination of protein and nucleic acid components. X. A comparison between the crystal and molecular structures of L-tyrosine and L-tyrosine hydrochloride".J. Chem. Phys.58 (6):2547–2556.Bibcode:1973JChPh..58.2547F.doi:10.1063/1.1679537.
^Lindemann L, Hoener MC (May 2005). "A renaissance in trace amines inspired by a novel GPCR family".Trends in Pharmacological Sciences.26 (5):274–281.doi:10.1016/j.tips.2005.03.007.PMID15860375.
^Wang X, Li J, Dong G, Yue J (February 2014). "The endogenous substrates of brain CYP2D".European Journal of Pharmacology.724:211–218.doi:10.1016/j.ejphar.2013.12.025.PMID24374199.
^Bentinger M, Tekle M, Dallner G (May 2010). "Coenzyme Q--biosynthesis and functions".Biochemical and Biophysical Research Communications.396 (1):74–9.doi:10.1016/j.bbrc.2010.02.147.PMID20494114.
^Molnár GA, Nemes V, Biró Z, Ludány A, Wagner Z, Wittmann I (December 2005). "Accumulation of the hydroxyl free radical markers meta-, ortho-tyrosine and DOPA in cataractous lenses is accompanied by a lower protein and phenylalanine content of the water-soluble phase".Free Radical Research.39 (12):1359–66.doi:10.1080/10715760500307107.PMID16298866.S2CID31154432.
^Rasmussen DD, Ishizuka B, Quigley ME, Yen SS (October 1983). "Effects of tyrosine and tryptophan ingestion on plasma catecholamine and 3,4-dihydroxyphenylacetic acid concentrations".The Journal of Clinical Endocrinology and Metabolism.57 (4):760–3.doi:10.1210/jcem-57-4-760.PMID6885965.
^Leathwood PD, Pollet P (1982). "Diet-induced mood changes in normal populations".Journal of Psychiatric Research.17 (2):147–54.doi:10.1016/0022-3956(82)90016-4.PMID6764931.
^Lieberman HR, Corkin S, Spring BJ, Wurtman RJ, Growdon JH (August 1985). "The effects of dietary neurotransmitter precursors on human behavior".The American Journal of Clinical Nutrition.42 (2):366–70.doi:10.1093/ajcn/42.2.366.PMID4025206.
^abLütke-Eversloh T, Santos CN, Stephanopoulos G (December 2007). "Perspectives of biotechnological production of L-tyrosine and its applications".Applied Microbiology and Biotechnology.77 (4):751–62.doi:10.1007/s00253-007-1243-y.PMID17968539.S2CID23088822.
^Chavez-Bejar M, Baez-Viveros J, Martinez A, Bolivar F, Gosset G (2012). "Biotechnological production of L-tyrosine and derived compounds".Process Biochemistry.47 (7):1017–1026.doi:10.1016/j.procbio.2012.04.005.
