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 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 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.[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 via SH2 domain binding.[10]
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 the four core manganese clusters.[11]
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.[12]
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.[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 acid phenylalanine (Phe), which is derived from food. The conversion of Phe to Tyr is catalyzed by the enzymephenylalanine hydroxylase, a monooxygenase. This enzyme catalyzes the reaction causing the addition of a hydroxyl group to the end of 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 the addition of a sulfate group, a process known as tyrosine sulfation.[17]Tyrosine sulfation is catalyzed by tyrosylprotein sulfotransferase (TPST). Like the phosphotyrosine antibodies mentioned above, antibodies have recently been described that specifically detect sulfotyrosine.[18]
The latex of Papaver somniferum, the opium poppy, has been shown to convert tyrosine into the alkaloidmorphine 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 transforms L-tyrosine into p-coumaric acid.Tyrosine is also the precursor to the pigment melanin. Tyrosine (or its precursor phenylalanine) is needed to synthesize the benzoquinone structure which forms part of coenzyme Q10.[23][24]
The decomposition of tyrosine to acetoacetate and fumarate. Two dioxygenases are necessary for the decomposition path. The end products can then enter into the citric acid cycle.
The decomposition of L-tyrosine (syn. para-hydroxyphenylalanine) begins with an α-ketoglutarate dependent transamination through the tyrosine transaminasetopara-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).
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.
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.[27][28]
Tyrosine is a precursor to neurotransmitters 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 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".[33]
L-tyrosine 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.[34] Advances in genetic engineering and the advent of industrial fermentation have shifted the synthesis of L-tyrosine to the use of engineered strains of E. 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.
