Tyrosine
- ( S) - ( -)- tyrosine,
- D-( ) -tyrosine
- (R) - ( ) -tyrosine
- P- hydroxyphenylalanine
- 2-amino- 3-( 4-hydroxyphenyl ) propionic acid
- 2-amino- 3-(4 -hydroxyphenyl) propanoic acid
- Abbreviations: Tyr ( Three letter code)
- 556-02-5 (D - tyrosine)
- 556-40-6 (DL- tyrosine)
Colorless, silky needles
1.46 g · cm -3 ( 25 ° C)
342-344 ° C ( decomposition)
- PKCOOH: 2.20
- PKNH2: 9.11
- PKPh - OH: 10.07
- Readily soluble in acids and alkalis
- Sparingly soluble in water (0.38 g · l-1 at 20 ° C)
- Insoluble in ethanol, ether and acetone,
5110 mg · kg -1 ( LD50, mouse, oral)
Template: Infobox chemical / molecular formula search available
Tyrosine ( Tyr or abbreviated Y) ( " proteinogenic " ) in its native L- form of a non-essential α - amino acid found in most proteins. Tyrosine is a starting material for the biosynthesis of DOPA, dopamine, catecholamines, melanin, thyroxine and tyramine. The biosynthesis occurs in many animals from the essential amino acid phenylalanine, an impairment of this pathway can cause a variety of defects.
If in this text or in the scientific literature " tyrosine " without further suffix (prefix ) is mentioned, L- tyrosine is meant.
- 4.1 biogenesis
- 4.2 precursor
- 4.3 pathophysiology
- 4.4 reduction
Occurrence
L- tyrosine from cheese ( gr τυρός, tyros, cheese ') was first isolated, hence also the name comes from, it comes in large amounts in casein.
The following examples provide an overview of Tyrosingehalte and are each based on 100 g of food, in addition, the percentage of tyrosine is indicated at the total protein:
All of these foods contain almost exclusively chemically bound L- tyrosine protein component, but no free L- tyrosine.
History
L- tyrosine was characterized first time in 1846 by Justus von Liebig as a protein constituent of cheese.
Properties
As a monomer
Depending on the pH value can be present as " inner salt " or zwitterion tyrosine. The proton of the carboxyl group is superimposed here on to the free electron pair of the nitrogen atom of the amino group:
In the electric field zwitterions do not migrate because they are uncharged back to the outside. The isoelectric point is at pH 5.66 for tyrosine; at this pH value is tyrosine at least soluble in water.
Isolated L-tyrosine fluorescence - as many other aromatic compounds - when excited with UV light.
- Van der Waals volume of 141
- Hydrophobicity: -1.3
In proteins
L-tyrosine is required during the translation of the structure of many proteins.
Of special significance is the L- tyrosine in proteins involved in signal transduction. It acts as a receiver of phosphate groups by protein kinases (known as receptor tyrosine kinases ), and are transmitted to change the target protein in its activity.
It also plays an important role in photosynthesis by reducing in photosystem II as an electron donor, the oxidized chlorophyll. Here, it loses its initially the proton phenolic OH group is a neutral radical and is then reduced again by the present in photosystem II tetranuclear manganese clusters.
Metabolism
Biogenesis
Plants and most microorganisms synthesize tyrosine via the Shikimisäureweg.
In the animal body caused by biopterin dependent tyrosine 4 -hydroxylation on the phenyl ring of L- phenylalanine. The enzyme catalyzing this reaction is the phenylalanine hydroxylase, a monooxygenase. In this case, an oxygen molecule (O2) is needed and in this reaction, a water molecule is formed ( H2O). The precursor, the essential amino acid L- phenylalanine is taken with food
As a result of phenylketonuria ( PKU) can cause a deficiency of L - tyrosine. About ingested L- phenylalanine can not be correctly hydroxylated in the para position it so that no L- tyrosine can be formed from phenylalanine. In this case must be supplied to the body of L-tyrosine.
Precursor
Tyrosine can serve as a starting material ( precursor ) for other required materials:
DOPA in turn, is the precursor for neurotransmitters or melanin. Particularly in the adrenal medulla is performed by the enzyme aromatic L- amino acid decarboxylase production of catechols neurotransmitters adrenaline and noradrenaline, which are released into the blood when required. The production of dopamine from DOPA occurs membrane bound by nerve cells. Melanin is especially manufactured and stored by melanocytes of the skin and hair as well as by pigment cells of the eyes from DOPA.
Pathophysiology
In nitrosative stress nitrotyrosine is formed from peroxynitrite and tyrosine by nucleophilic aromatic substitution. Nitrotyrosine used in laboratory diagnostics as a biomarker of nitrosative stress or apoptosis (programmed cell death).
Reduction
The degradation of L - tyrosine ( p- hydroxyphenylalanine ) begins with an α -ketoglutarate - dependent transamination of L- tyrosine to p -hydroxyphenylpyruvate transaminase.
The next step catalyzes the 4 -hydroxyphenylpyruvate dioxygenase with incorporation of oxygen and elimination of CO 2 to homogentisate (2,5- dihydroxyphenyl - 1-acetate ). To cleave the aromatic ring of Homogentisats, a further dioxygenase that homogentisate oxygenase required. This is caused by intercalation of another O2 molecule the Maleylacetacetat.
Maleylacetacetat the cis-trans isomerase is produced in this case by rotating the Fumarylacetat by oxidation ( from the hydroxyl group ) formed carboxyl. This cis-trans isomerase contains glutathione as coenzyme. Fumarylacetacetat may eventually be cleaved by the hydrolase Fumarylacetacetat caused by fluid retention.
Here are free fumarate (also a metabolite of the citric acid cycle ) and acetoacetate ( butane -(3 ) -on- acid). Acetoacetate is a ketone body, which is activated by succinyl -CoA, and then into two molecules of acetyl- CoA ( for the citric acid cycle and fatty acid synthesis) can be implemented.
Applications
Tyrosine is a precursor of neurotransmitters (particularly dopamine and norepinephrine) but has little influence on the mood. High doses of tyrosine lower dopamine levels.
Some studies found a benefit under stress, cold or fatigue. However, the tyrosine hydroxylase is the rate- determining factor of the conversion, so that the effects are lower than for L -DOPA.
Supply of L- tyrosine serves as replacement therapy or supplementation in deficiency, such as phenylketonuria, otherwise results in a lower production of melanin ( albinism ) and L- thyroxine ( cretinism ). In addition, problems exist in the production of catecholamines.
L- tyrosine is used due to its protein - adsorbing properties for years as adjuvant depot carrier in the specific subcutaneous immunotherapy ( SCIT ). L- tyrosine is distinguished from other depository institutions ( aluminum hydroxide, calcium phosphate) while among others, by the advantage of the full metabolised and short half -life of 48 hours at the injection site.
Production
The acid hydrolysis of keratin proteins result after the neutralization a protein consisting of the 20 proteinogenic α -amino acids. This results in an L- cysteine and L-tyrosine - rich fraction can easily win by separating the highly water-soluble amino acids because L- cysteine and L-tyrosine dissolve only slightly in water. To date, L- tyrosine is obtained commercially by this simple separation method.