Information AboutTyrosine |
| CATEGORIES ABOUT TYROSINE | |
| proteinogenic amino acids | |
| glucogenic amino acids | |
| ketogenic amino acids | |
| aromatic amino acids | |
| phenols | |
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Tyrosine (from the s that are used by Cells to Synthesize Protein s. 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 Levodopa by the enzyme Tyrosine Hydroxylase . Some of the tyrosine residues can be ''tagged'' with a phosphate group ( Phosphorylated ) by Protein Kinase s. (In its phosphorylated state, it is referred to as phosphotyrosine.). Tyrosine phosphorylation is considered as 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 . Tyrosine Sulfation is catalyzed by tyrosylprotein sulfotransferase (TPST). Like the phosphotyrosine antibodies mentioned above, antibodies have recently been described that specifically detect sulfotyrosine. Tyrosine is also precursor to the Thyroid Hormone s '' Thyroxine '' and '' Triiodothyronine '', the pigment '' Melanin '', and the biologically-active Catecholamine s '' Dopamine '', '' Norepinephrine '' and '' Epinephrine ''. In Papaver Somniferum , the opium poppy, it is used to produce Morphine . __NOTOC__ 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 such as Dopamine , Norepinephrine and Epinephrine . MEDICAL USE L-Tyrosine is sometimes recommended by practitioners as helpful for Weight Loss , Clinical Depression , Parkinson's Disease , Attention Deficit Disorder and Phenylketonuria ; however, one study found that it had no impact on endurance exercise performance. Parcell A.C., et al. Effects of L-tyrosine and carbohydrate ingestion on performance. Journal of Applied Physiology 2002 Nov; 93(5): 1590-97. Abstract SEE ALSO REFERENCES
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