Editing Tyrosine (section)

==Metabolism==

[[File:Conversion of phenylalanine and tyrosine to its biologically important derivatives.png|center|thumb|800px|Conversion of phenylalanine and tyrosine to its biologically important derivatives.]]

=== Phosphorylation and sulfation ===
Some of the tyrosine residues can be ''tagged'' (at the hydroxyl group) with a phosphate group ([[phosphorylation|phosphorylated]]) by [[protein kinase]]s. 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 [[antibody|antibodies]].  Tyrosine residues may also be modified by the addition of a sulfate group, a process known as [[tyrosine sulfation]].<ref name="pmid17046811">{{cite journal | vauthors = Hoffhines AJ, Damoc E, Bridges KG, Leary JA, Moore KL | title = Detection and purification of tyrosine-sulfated proteins using a novel anti-sulfotyrosine monoclonal antibody | journal = The Journal of Biological Chemistry | volume = 281 | issue = 49 | pages = 37877–87 | date = December 2006 | pmid = 17046811 | pmc = 1764208 | doi = 10.1074/jbc.M609398200 | doi-access = free }}</ref> [[Tyrosine sulfation]] is catalyzed by [[tyrosylprotein sulfotransferase]] (TPST).  Like the phosphotyrosine antibodies mentioned above, antibodies have recently been described that specifically detect sulfotyrosine.<ref>{{cite journal | vauthors = Kanan Y, Hamilton RA, Sherry DM, Al-Ubaidi MR | title = Focus on molecules: sulfotyrosine | journal = Experimental Eye Research | volume = 105 | pages = 85–6 | date = December 2012 | pmid = 22406006 | pmc = 3629733 | doi = 10.1016/j.exer.2012.02.014 }}</ref>

===Precursor to neurotransmitters and hormones===
In dopaminergic cells in the [[brain]], tyrosine is converted to [[L-DOPA]] by the [[enzyme]] [[tyrosine hydroxylase]] (TH).  TH is the [[rate-limiting enzyme]] involved in the synthesis of the [[neurotransmitter]] [[dopamine]]. Dopamine can then be converted into other [[catecholamine]]s, such as [[norepinephrine]] (noradrenaline) and [[epinephrine]] (adrenaline).

The [[thyroid]] hormones [[triiodothyronine]] (T<sub>3</sub>) and [[thyroxine]] (T<sub>4</sub>) in the [[colloid]] of the [[thyroid]] are also derived from tyrosine.
{{Phenylalanine biosynthesis|caption=Tyrosine is a precursor to trace amine compounds and the catecholamines.}}

=== Precursor to other compounds ===
The latex of ''[[Papaver somniferum]]'', 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.<ref>{{Cite journal |last1=Battersby |first1=A. R. |last2=Binks |first2=R. |last3=Harper |first3=B. J. T. |date=1962-01-01 |title=692. Alkaloid biosynthesis. Part II. The biosynthesis of morphine |url=https://pubs.rsc.org/en/content/articlelanding/1962/jr/jr9620003534 |journal=Journal of the Chemical Society  |language=en |pages=3534–3544 |doi=10.1039/JR9620003534 |issn=0368-1769}}</ref>[[Tyrosine ammonia lyase]] (TAL) is an enzyme in the natural phenols biosynthesis pathway. It transforms <small>L</small>-tyrosine into [[p-Coumaric acid|''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]].<ref>{{Cite journal |vauthors=Bentinger M, Tekle M, Dallner G |date=May 2010 |title=Coenzyme Q--biosynthesis and functions |journal=Biochemical and Biophysical Research Communications |volume=396 |issue=1 |pages=74–9 |doi=10.1016/j.bbrc.2010.02.147 |pmid=20494114}}</ref><ref>{{cite journal |doi=10.1016/j.bbabio.2016.03.036 |title=Coenzyme Q biosynthesis in health and disease |date=2016 |last1=Acosta |first1=Manuel Jesús |last2=Vazquez Fonseca |first2=Luis |last3=Desbats |first3=Maria Andrea |last4=Cerqua |first4=Cristina |last5=Zordan |first5=Roberta |last6=Trevisson |first6=Eva |last7=Salviati |first7=Leonardo |journal=Biochimica et Biophysica Acta (BBA) - Bioenergetics |volume=1857 |issue=8 |pages=1079–1085 |pmid=27060254 |doi-access=free }}</ref>

=== Degradation ===
[[Image:Tyrosinedegradation2.png|thumb|center|750px|The decomposition of tyrosine to [[acetoacetic acid|acetoacetate]] and [[fumarate]].  Two dioxygenases are necessary for the decomposition path.  The end products can then enter into the [[citric acid cycle]].]]{{citation needed|date=November 2023}}

<!-- This path is described in Stryer reference -->
The decomposition of <small>L</small>-tyrosine (syn. ''para''-hydroxyphenylalanine) begins with an α-ketoglutarate dependent [[transamination]] through the [[tyrosine transaminase]] to [[para-Hydroxyphenylpyruvate|''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-Hydroxyphenylpyruvate dioxygenase|''p''-hydroxyphenylpyruvate dioxygenase]] and splitting off CO<SUB>2</SUB> [[homogentisic acid|homogentisate]] (2,5-dihydroxyphenyl-1-acetate).<ref>{{cite journal | vauthors = Zea-Rey AV, Cruz-Camino H, Vazquez-Cantu DL, Gutiérrez-García VM, Santos-Guzmán J, Cantú-Reyna C |title=The Incidence of Transient Neonatal Tyrosinemia Within a Mexican Population |journal=Journal of Inborn Errors of Metabolism and Screening |date=27 November 2017 |volume=5 |pages=232640981774423 |doi=10.1177/2326409817744230|doi-access=free }}</ref>  In order to split the aromatic ring of homogentisate, a further dioxygenase, [[homogentisate 1,2-dioxygenase]] is required.  Thereby, through the incorporation of a further O<SUB>2</SUB> molecule, [[maleylacetoacetate]] is created.

[[Fumarylacetoacetate]] is created by [[4-maleylacetoacetate cis-trans-isomerase|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 the addition of a water molecule.

Thereby [[fumarate]] (also a metabolite of the citric acid cycle) and [[acetoacetic acid|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 a urinary metabolite of tyrosine in rats.<ref>{{cite journal | vauthors = Booth AN, Masri MS, Robbins DJ, Emerson OH, Jones FT, DeEds F | year = 1960 | title = Urinary phenolic acid metabolities of tyrosine | url = http://www.jbc.org/content/235/9/2649.citation | journal = Journal of Biological Chemistry | volume = 235 | issue = 9| pages = 2649–2652 | doi = 10.1016/S0021-9258(19)76930-0 | doi-access = free }}</ref>