PHENYLALANINE (US: /ˌfɛnəlˈæləniːn/ , UK:
/ˌfiːnaɪlˈæləniːn/ ; abbreviated as PHE or F) is an α-amino
acid with the formula C
2. It can be viewed as a benzyl group substituted for the methyl
group of alanine , or a phenyl group in place of a terminal hydrogen
of alanine. This essential amino acid is classified as neutral, and
nonpolar because of the inert and hydrophobic nature of the benzyl
side chain. The L-isomer is used to biochemically form proteins ,
coded for by
* 1 History
* 2 Dietary sources * 3 Requirements
* 4 Other biological roles
* 4.1 In plants
The first description of phenylalanine was made in 1879, when Schulze and Barbieri identified a compound with the empirical formula , C9H11NO2, in yellow lupine (Lupinus luteus) seedlings. In 1882, Erlenmeyer and Lipp first synthesized phenylalanine from phenylacetaldehyde , hydrogen cyanide, and ammonia.
The genetic codon for phenylalanine was first discovered by J. Heinrich Matthaei and Marshall W. Nirenberg in 1961. They showed that by using mRNA to insert multiple uracil repeats into the genome of the bacterium E. coli , they could cause the bacterium to produce a polypeptide consisting solely of repeated phenylalanine amino acids. This discovery helped to establish the nature of the coding relationship that links information stored in genomic nucleic acid with protein expression in the living cell.
As an essential amino acid, phenylalanine is not synthesized de novo in humans and other animals, who must ingest phenylalanine or phenylalanine-containing proteins.
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Good sources of phenylalanine are eggs, chicken, liver, beef, milk, and soybeans.
The Food and Nutrition Board (FNB) of the U.S. Institute of Medicine set Recommended Dietary Allowances (RDAs) for essential amino acids in 2002. For phenylalanine plus tyrosine, for adults 19 years and older, 33 mg/kg body weight/day.
OTHER BIOLOGICAL ROLES
L-Phenylalanine is biologically converted into L-tyrosine , another one of the DNA-encoded amino acids. L-tyrosine in turn is converted into L-DOPA , which is further converted into dopamine , norepinephrine (noradrenaline), and epinephrine (adrenaline). The latter three are known as the catecholamines .
Biosynthetic pathways for catecholamines and trace amines in the
human brain L-PHENYLALANINE L-
The genetic disorder phenylketonuria (PKU) is the inability to metabolize phenylalanine because of a lack of the enzyme phenylalanine hydroxylase . Individuals with this disorder are known as "phenylketonurics" and must regulate their intake of phenylalanine. A (rare) "variant form" of phenylketonuria called hyperphenylalaninemia is caused by the inability to synthesize a cofactor called tetrahydrobiopterin , which can be supplemented. Pregnant women with hyperphenylalaninemia may show similar symptoms of the disorder (high levels of phenylalanine in blood) but these indicators will usually disappear at the end of gestation. Pregnant women with PKU must control their blood phenylalanine levels even if the fetus is heterozygous for the defective gene because the fetus could be adversely affected due to hepatic immaturity. Individuals who cannot metabolize phenylalanine must monitor their intake of protein to control the buildup of phenylalanine as their bodies convert protein into its component amino acids.
Phenylketonurics often use blood tests to monitor the amount of phenylalanine in their blood. Lab results may report phenylalanine levels in different units, including mg/dL and μmol/L. One mg/dL of phenylalanine is approximately equivalent to 60 μmol/L.
A non-food source of phenylalanine is the artificial sweetener aspartame . This compound, sold under the trade names Equal and NutraSweet , is metabolized by the body into several chemical byproducts including phenylalanine. The breakdown problems phenylketonurics have with protein and the attendant buildup of phenylalanine in the body also occurs with the ingestion of aspartame, although to a lesser degree. Accordingly, all products in Australia, the U.S. and Canada that contain aspartame must be labeled: "Phenylketonurics: Contains phenylalanine." In the UK, foods containing aspartame must carry ingredient panels that refer to the presence of "aspartame or E951" and they must be labeled with a warning "Contains a source of phenylalanine." In Brazil, the label "Contém Fenilalanina" (Portuguese for "Contains Phenylalanine") is also mandatory in products which contain it. These warnings are placed to aid individuals who have been diagnosed with PKU so that they can avoid such foods.
Geneticists have recently sequenced the genome of macaques . Their investigations have found "some instances where the normal form of the macaque protein looks like the diseased human protein" including markers for PKU.
D-, L- AND DL-PHENYLALANINE
The stereoisomer D-phenylalanine (DPA) can be produced by conventional organic synthesis , either as a single enantiomer or as a component of the racemic mixture. It does not participate in protein biosynthesis although it is found in proteins in small amounts - particularly aged proteins and food proteins that have been processed . The biological functions of D-amino acids remain unclear, although D-phenylalanine has pharmacological activity at niacin receptor 2 .
L-Phenylalanine (DLPA) is marketed as a nutritional supplement for
its purported analgesic and antidepressant activities.
L-Phenylalanine is a mixture of D-phenylalanine and L-phenylalanine.
The reputed analgesic activity of DL-phenylalanine may be explained by
the possible blockage by D-phenylalanine of enkephalin degradation by
the enzyme carboxypeptidase A . The mechanism of DL-phenylalanine's
supposed antidepressant activity may be accounted for by the precursor
role of L-phenylalanine in the synthesis of the neurotransmitters
norepinephrine and dopamine . Elevated brain levels of norepinephrine
and dopamine are thought to have an antidepressant effect.
L-Phenylalanine is an antagonist at α2δ Ca2+ calcium channels with a Ki of 980 nM.
In the brain, L-phenylalanine is a competitive antagonist at the
glycine binding site of
NMDA receptor and at the glutamate binding
L-Phenylalanine is produced for medical, feed, and nutritional applications, such as aspartame , in large quantities by utilizing the bacterium Escherichia coli , which naturally produces aromatic amino acids like phenylalanine. The quantity of L-phenylalanine produced commercially has been increased by genetically engineering E. coli, such as by altering the regulatory promoters or amplifying the number of genes controlling enzymes responsible for the synthesis of the amino acid.
BORONOPHENYLALANINE (BPA) is a dihydroxyboryl derivative of phenylalanine, used in neutron capture therapy .
* ^ Dawson RM, et al. (1959). Data for Biochemical Research.
Oxford: Clarendon Press.
* ^ IUPAC-IUBMB Joint Commission on Biochemical Nomenclature
(1983). "Nomenclature and Symbolism for Amino Acids and Peptides".
Recommendations on Organic & Biochemical Nomenclature, Symbols &
Terminology etc. Retrieved 2007-05-17.
* ^ Thorpe TE (1913). A Dictionary of Applied Chemistry. Longmans,
Green, and Co. pp. 191–193. Retrieved 2012-06-04.
* ^ Plimmer RH (1912) . Plimmer RH, Hopkins FG, eds. The Chemical
Composition of the Proteins. Monographs on Biochemistry. Part I.
Analysis (2nd ed.). London: Longmans, Green and Co. pp. 93–97.
* ^ Ross HM, Roth J (1 April 1991). The Mood Control Diet: 21 Days
to Conquering Depression and Fatigue. Simon & Schuster. p. 59. ISBN
Institute of Medicine (2002). "
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