Phenylalanine

"Phe" redirects here. For other uses, see Phe (disambiguation).
Phenylalanine

L-Phenylalanine

L-Phenylalanine at physiological pH
Names
IUPAC name
Phenylalanine
Other names
2-Amino-3-phenylpropanoic acid
Identifiers
150-30-1 (DL) YesY
63-91-2 (L) YesY
ChEBI CHEBI:58095 YesY
ChEMBL ChEMBL301523 YesY
ChemSpider 5910 YesY
DrugBank DB00120 N
3313
KEGG D00021 YesY
PubChem 994
UNII 8P946UF12S YesY
Properties
C6H5CH2CH(NH2)COOH
Acidity (pKa) 1.83 (carboxyl), 9.13 (amino)[1]
Hazards
Safety data sheet See: data page
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
1
2
0
Supplementary data page
Refractive index (n),
Dielectric constant (εr), etc.
Thermodynamic
data
 Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
N verify (what is YesYN ?)
Infobox references

Phenylalanine /ˌfɛnᵊlˈæləˌniːn/ (abbreviated as Phe or F)[2] is an α-amino acid with the formula C6H5CH2CH(NH2)COOH. 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 DNA. The codons for L-phenylalanine are UUU and UUC. Phenylalanine is a precursor for tyrosine, the monoamine neurotransmitters dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline), and the skin pigment melanin.

Phenylalanine is found naturally in the breast milk of mammals. It is used in the manufacture of food and drink products and sold as a nutritional supplement for its reputed analgesic and antidepressant effects. It is a direct precursor to the neuromodulator phenethylamine, a commonly used dietary supplement.

History

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.[3][4]

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.

Biosynthesis

As an essential amino acid, phenylalanine is not synthesized de novo in humans and other animals, who must ingest phenylalanine or phenylalanine-containing proteins.

Dietary sources

Good sources of phenylalanine are eggs, chicken, liver, beef, milk, and soybeans.[5] Other sources include spinach and leafy greens, tofu, amaranth leaves, and lupin seeds.

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.

Phenylalanine uses the same active transport channel as tryptophan to cross the blood–brain barrier. In excessive quantities, supplementation can interfere with the production of serotonin and other aromatic amino acids as well as nitric oxide due to the overuse (eventually, limited availability) of the associated cofactors, iron or tetrahydrobiopterin. The corresponding enzymes in for those compounds are the aromatic amino acid hydroxylase family and nitric oxide synthase.

Human biosynthesis pathway for trace amines and catecholamines[6][7]
Graphic of trace amine and catecholamine metabolism
The image above contains clickable links
Phenylalanine in humans may ultimately be metabolized into a range of different substances.

In plants

Phenylalanine is the starting compound used in the synthesis of flavonoids. Lignan is derived from phenylalanine and from tyrosine. Phenylalanine is converted to cinnamic acid by the enzyme phenylalanine ammonia-lyase.[8]

Phenylketonuria

Main article: Phenylketonuria

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. 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"[9] 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.[10]

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.[11]

DL-Phenylalanine (DLPA) is marketed as a nutritional supplement for its supposed analgesic and antidepressant activities. DL-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.[12] 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. D-Phenylalanine is absorbed from the small intestine and transported to the liver via the portal circulation. A small amount of D-phenylalanine appears to be converted to L-phenylalanine. D-Phenylalanine is distributed to the various tissues of the body via the systemic circulation. It appears to cross the blood–brain barrier less efficiently than L-phenylalanine, and so a small amount of an ingested dose of D-phenylalanine is excreted in the urine without penetrating the central nervous system.

L-Phenylalanine is an antagonist at α2δ Ca2+ calcium channels with a Ki of 980 nM.[13] At higher doses, this may play a role in its analgesic and antidepressant properties.

In the brain, L-phenylalanine is a competitive antagonist at the glycine binding site of NMDA receptor[14] and at the glutamate binding site of AMPA receptor.[15] At the glycine binding site of NMDA receptor L-phenylalanine has an apparent equilibrium dissociation constant (KB) of 573 µM estimated by Schild regression[16] which is considerably lower than brain L-phenylalanine concentration observed in untreated human phenylketonuria.[17] L-Phenylalanine also inhibits neurotransmitter release at glutamatergic synapses in hippocampus and cortex with IC50 of 980 µM, a brain concentration seen in classical phenylketonuria, whereas D-phenylalanine has a significantly smaller effect.[15]

Commercial synthesis

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.[18]

References

  1. ↑ Dawson, R. M. C.; et al. (1959). Data for Biochemical Research. Oxford: Clarendon Press.
  2. ↑ 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.
  3. ↑ Thorpe, T. E. (1913). A Dictionary of Applied Chemistry. Longmans, Green, and Co. pp. 191–193. Retrieved 2012-06-04.
  4. ↑ Plimmer, R. H. A. (1912) [1908]. Plimmer, R. H. A.; Hopkins, F. G., ed. The Chemical Composition of the Proteins. Monographs on Biochemistry. Part I. Analysis (2nd ed.). London: Longmans, Green and Co. pp. 93–97. Retrieved 2012-06-04.
  5. ↑ Harvey M. Ross; June Roth (1 April 1991). The Mood Control Diet: 21 Days to Conquering Depression and Fatigue. Simon & Schuster. p. 59. ISBN 978-0-13-590449-7.
  6. ↑ Broadley KJ (March 2010). "The vascular effects of trace amines and amphetamines". Pharmacol. Ther. 125 (3): 363–375. doi:10.1016/j.pharmthera.2009.11.005. PMID 19948186.
  7. ↑ Lindemann L, Hoener MC (May 2005). "A renaissance in trace amines inspired by a novel GPCR family". Trends Pharmacol. Sci. 26 (5): 274–281. doi:10.1016/j.tips.2005.03.007. PMID 15860375.
  8. ↑ Nelson, D. L.; Cox, M. M. (2000). Lehninger, Principles of Biochemistry (3rd ed.). New York: Worth Publishing. ISBN 1-57259-153-6.
  9. ↑ "Aspartame". UK: Food Standards Agency.
  10. ↑ Gibbs, R. A.; et al. (2007). "Evolutionary and Biomedical Insights from the Rhesus Macaque Genome" (pdf). Science 316 (5822): 222–234. doi:10.1126/science.1139247. PMID 17431167.
  11. ↑ "D-phenylalanine". IUPHAR. Retrieved 24 June 2014.
  12. ↑ Christianson, D. W.; Mangani, S.; Shoham, G.; Lipscomb, W. N. (1989). "Binding of D-Phenylalanine and D-Tyrosine to Carboxypeptidase A" (pdf). Journal of Biological Chemistry 264 (22): 12849–12853. PMID 2568989.
  13. ↑ Mortell KH, Anderson DJ, Lynch JJ, et al. (March 2006). "Structure-activity relationships of alpha-amino acid ligands for the alpha2delta subunit of voltage-gated calcium channels". Bioorganic & Medicinal Chemistry Letters 16 (5): 1138–41. doi:10.1016/j.bmcl.2005.11.108. PMID 16380257.
  14. ↑ Glushakov, AV; Dennis, DM; Morey, TE; Sumners, C; Cucchiara, RF; Seubert, CN; Martynyuk, AE (2002). "Specific inhibition of N-methyl-D-aspartate receptor function in rat hippocampal neurons by L-phenylalanine at concentrations observed during phenylketonuria.". Molecular Psychiatry 7 (4): 359–67. doi:10.1038/sj.mp.4000976. PMID 11986979.
  15. 1 2 Glushakov, AV; Dennis, DM; Sumners, C; Seubert, CN; Martynyuk, AE (Apr 1, 2003). "L-phenylalanine selectively depresses currents at glutamatergic excitatory synapses.". Journal of neuroscience research 72 (1): 116–24. doi:10.1002/jnr.10569. PMID 12645085.
  16. ↑ Glushakov, AV; Glushakova, O; Varshney, M; Bajpai, LK; Sumners, C; Laipis, PJ; Embury, JE; Baker, SP; Otero, DH; Dennis, DM; Seubert, CN; Martynyuk, AE (February 2005). "Long-term changes in glutamatergic synaptic transmission in phenylketonuria.". Brain : a journal of neurology 128 (Pt 2): 300–7. doi:10.1093/brain/awh354. PMID 15634735.
  17. ↑ Möller, HE; Weglage, J; Bick, U; Wiedermann, D; Feldmann, R; Ullrich, K (December 2003). "Brain imaging and proton magnetic resonance spectroscopy in patients with phenylketonuria.". Pediatrics 112 (6 Pt 2): 1580–3. PMID 14654669.
  18. ↑ Sprenger, G. A. (2007). "Aromatic Amino Acids". Amino Acid Biosynthesis: Pathways, Regulation and Metabolic Engineering (1st ed.). Springer. pp. 106–113. ISBN 978-3-540-48595-7.

External links

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