Article: Tyrosine

Tyrosine
Systematic_name	(S)-2-Amino-3-(4-hydroxy- phenyl)-propanoic acid
Abbreviations	Tyr Y
Chemical formula	C9H11NO3
Molecular mass	181.19 g mol-1
Melting point	343 °C
Density	1.456 g cm-3
Isoelectric point	5.66
pKa	2.24 9.04 10.10
CAS number	[60-18-4]
EINECS number	200-460-4
SMILES	Oc1ccc(CC(N)C(=O)O)cc1
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Tyrosine (from the Greek tyros, meaning cheese, as it was first discovered in cheese), 4-hydroxyphenylalanine, or 2-amino-3(4-hydroxyphenyl)-propanoic acid, is one of the 20 amino acids that are used by cells to synthesize proteins. It has a phenol side chain with a hydroxyl group. Upon the location of the hydroxyl group, there are three structural isomers of Tyr, namely para-Tyr (p-Tyr), meta-Tyr (m-Tyr) and ortho-Tyr (o-Tyr). Enzymatically, only the first isomer (p-Tyr) is produced from L-Phe by the Phe-hydroxylase enzyme. The other two isoforms, m-Tyr and o-Tyr can be produced as a consequence of free radical attack on Phe in states with increased oxidative stress.

Tyrosine is converted to DOPA by tyrosine hydroxylase, an enzyme.

It plays a key role in signal transduction, since it can be tagged with a phosphate group (phosphorylated) by protein kinases to alter the functionality and activity of certain enzymes. (In its phosphorylated state, it is sometimes referred to as phosphotyrosine.) Tyrosine is also precursor to the thyroid hormones thyroxine and triiodothyronine, the pigment melanin, and the biologically-active catecholamines dopamine, norepinephrine and epinephrine.

In Papaver somniferum, the opium poppy, it is used to produce morphine.

Biosynthesis

Tyrosine cannot be completely synthesized by animals, although it can be made by hydroxylation of phenylalanine if the latter is in abundant supply. It is produced by plants and most microorganisms from prephenate, an intermediate on the shikimate pathway.

Prephenate is oxidatively decarboxylated with retention of the hydroxyl group to give p-hydroxyphenylpyruvate. This is transaminated using glutamate as the nitrogen source to give tyrosine and α-ketoglutarate.

Tyrosine hydroxylase

Tyrosine hydroxylase (TH) is the rate-limiting enzyme involved in the synthesis of the catecholamines (Dopamine, Norepinephrine, Epinephrine).

See also

• Tyramine
• Alkaptonuria
• Tyrosinemia
• Albinism